Microhydro Myths & Misconceptions


Inside this Article

Closed-Loop Hydro Myth
Myth 1: Closed-Loop / Pumped Storage
Downspout Hydro Myth
Myth 2: Rooftop / Downspout Hydro
Municipal Hydro Myth
Myth 3: Hydro from Municipal Water Supply
Pipe Size Hydro Myth
Myth 4: Reducing Pipe Size to Increase Pressure / Power
In-Flow Hydro Myth
Myth 5: In-Flow / No-Head Systems
Closed-Loop Hydro Myth
Downspout Hydro Myth
Municipal Hydro Myth
Pipe Size Hydro Myth
In-Flow Hydro Myth

Making electricity from falling water can seem like magic, and that’s led to lots of misconceptions. Here, we’ll separate fact from fiction when it comes to what microhydro systems can and cannot do.

Residential-scale microhydro-electric systems have the reputation of being the holy grail of home renewable-energy (RE) systems. While they lack some of the hype, magic, and bling of solar-electric (photovoltaic) systems, microhydro systems are a simple technology that most people can understand…at least in general. In this article, we’ll look at some common microhydro system misconceptions, most of which come from folks looking for shortcuts to the reward of cheap electricity. 

Modern microhydro equipment comes from proven technology based on designs that have changed very little over the decades. Pelton and turgo wheels, the typical spinning water-wheel component, were invented in 1870 and 1919, respectively. The point is, this technology has proven its reliability and functionality with more than a century of performance.

The cost of these systems, and thus the cost of the resulting electricity, also has the reputation for being very reasonable when compared to other renewable or home-generated sources. While PV module prices have recently dropped, they are still a high-tech and expensive commodity. Microhydro systems can arguably be considered low-tech, with civil works and pipelines often being the majority of the system cost. Of course, the actual cost varies significantly from site to site, and from system to system.

Another element that keeps microhydro-generated electricity low in cost, and thus high in desirability, is the system’s continuous duty cycle. While PV systems only produce electricity when the sun is shining (and wind-electric systems when the wind is blowing), microhydro systems aren’t affected by nightfall or weather blocking the sun. Even a small hydro resource can provide electricity 24 hours a day, and often 365 days a year (if the water source is year-round). The bottom line for any renewable energy system is the amount of energy it can produce annually. A low power source working all of the time can often produce a lot more energy than a more powerful source that only works intermittently.

So, why doesn’t everyone have a microhydro system? Herein lies the challenge. A viable hydro resource is dependent on the availability of falling water at, or near, the site of the electrical loads. It is the weight or pressure of that flowing water that spins the turbine to produce electrical energy. Not everyone has access to a stream or spring of adequate volume on their property, nor does everyone have the topography to create the vertical drop needed to pressurize that water with gravity. See the “Microhydro Rules” sidebar for a formula about how water flow and vertical pressure (head) combine to determine the power available from a potential hydro site. That site-assessment formula will help debunk some of the myths that follow.

Many microhydro misconceptions are a combination of misunderstanding some of the basic properties of physics, and an overzealous optimism about the potential of RE resources. Here, we hope to correct the misconceptions about physics, while at the same time further encouraging educated optimism. Once you’ve had a little reality check here, we suggest you read some of Home Power’s other articles on the basics of hydro site assessment and microhydro systems (see Access at the end of this article). Perhaps you really do have untapped hydro potential waiting for you.

Myth 1: Closed-Loop / Pumped Storage

By far, the most common flawed design that we hear about at Home Power is the closed-loop system—that is, some scheme to pump water for the hydro turbine, and then have the turbine produce the electrical power for the pump…ad infinitum. Some of these schemes are simple “hydro-in-a-bucket” designs where the pump is expected to pressurize the water for the hydro turbine. Others are more involved, planning to pump water uphill to a pond or tank, and then let gravity do the job of running the turbine. All the while, the designer is expecting to get extra usable electric power from the turbine’s output—beyond what the pump is using. Whether large or small, all of these designs suffer from the same flaw in thinking.

The first law of thermodynamics says that energy can neither be created nor destroyed. All of the energy systems (renewable and otherwise) that we rely upon convert existing energy into a form that we can use to do the work we want to do. In a hydro-electric system, the energy of moving water is transferred to a rotating shaft, converted to changing magnetic fields, and then converted to moving electrons (electricity). But at no point is energy created. If we use that energy to create magnetic fields again, spinning a shaft and pumping water up to a tank on a hill, we still haven’t created any energy. We’ve just changed its form again. 

In a perfect universe, perhaps it could be argued that such a pump and turbine arrangement could run perpetually. But it wouldn’t do us any good, because we want to use that electricity to do some work besides just running the pump. Using any electricity for other tasks would be robbing the pump of the power it needed to keep up with the turbine, and the loop’s interdependence would break down. That, and the fact that there are always other forces robbing energy from the system, means that such a loop wouldn’t run for long, and that no additional energy could be extracted from it.

Those additional energy-robbing forces, mostly friction, are the imperfections that cripple this closed-loop design. Every component of such a system has an operating efficiency of less than 100%. That means each conversion step in the process wastes some of the potential energy that the system started with. We know that energy is not being destroyed, but it is being allowed to escape the loop in the form of heat, vibration, and even noise. It is being converted into a form that we can’t readily use, or even recover. 

Let’s look at some typical microhydro system efficiency numbers:

  • Penstock (pipeline) efficiency = 95%
  • Nozzle and runner efficiency = 80%
  • Permanent-magnet alternator efficiency = 90%
  • Wiring and control efficiency = 98%

0.95 × 0.80 × 0.90 × 0.98 = 0.67

By the time the water has moved through this example microhydro generator system, only 67% of its initial potential energy has been converted to electricity. In fact, this would be considered very good performance—typical systems are about 55% efficient.

Now let’s consider the efficiencies of pumping that water back to the hydro intake for reuse: 

  • Pipe efficiency = 95%
  • Pump (motor and impeller) efficiency = 65%

0.95 × 0.65 × 0.67 (from above) = 0.41

By the time the water had gone all the way through the system, only 41% of it would be returned to the top of the intake. After a second loop around, only 17% (0.41 × 0.41) of the water would be left. 

If there isn’t a water supply with useful head and flow to start with, nothing will happen—the pump won’t run because it won’t have electricity; the hydro turbine won’t have electricity because the pump isn’t running. Adding water (or electricity) to “prime” the loop will make the loop operate only as long as the priming continues. 

This is where creative folks start asking questions about bigger water tanks; larger pipes with less friction loss; tanks on a tower for shorter pipe runs; more head, and less flow; less head and more flow; adding batteries (only 80% efficient themselves); or even just piping right from the pump to the turbine—anything to improve system efficiency. In fact, the simplest thing that could be done to get rid of inefficiencies would be to skip the water components altogether; just hook the shaft of a motor directly to the shaft of the alternator, and the alternators output wires directly to the motor (somehow, the fallacy in that thinking is easier for us to understand). But no matter the variables, the outcome will be the same—total efficiency will be less than 100% and no energy will be gained. 

Moving energy around and changing its form, like from chemical to mechanical to electrical, is only a way to lose some of it. These efficiency losses are part of the price we pay to get energy into a format that we can use. We can lose more, or we can lose less, but adding complexity is inefficiency and will never result in a net gain.

Myth 2: Rooftop / Downspout Hydro

A second common microhydro-electric scheme that we are often asked about is the viability of putting turbines on a home’s gutter downspouts to generate electricity from the rain. Some imaginative folks know enough about hydro to understand that the energy has to come from somewhere (in this case, from the forces of nature), and that the height of the roof can contribute head (pressure) to spin that turbine.

The mistake in this scenario is a simple and honest one of scale. While some hydro units have been designed that can function on low head, such as from the roofline of typical homes (and even lower), a hydro turbine’s power output is a product of head times flow. And it is a lack of significant flow that is the defeating factor in the power equation when relying on rooftop rainwater collection. The watershed drainages for even small streams are usually measured in thousands of acres or square miles. Home roofs, even big ones, are measured in mere thousands of square feet.

Let’s look at example calculations for a large house in a very rainy place—Seattle, Washington, gets about 40 inches of rain per year, with November being the rainiest month at an average of about 6 inches. 

Let’s assume that a tall two-story house would give us a 25-foot-high roof, and thus 25 feet of head. This 6,000-square-foot home has about 3,000 square feet of rainwater collection area (remember, it’s two stories). That means that in November, this house would receive about 1,500 cubic feet of rain, or 11,220 gallons.

If that rainfall came as a constant drizzle all month long, flow from the roof would be only about 1/4 gallon per minute. Currently there is no turbine on the market to work with that flows that low, but using our microhydro power formula (see sidebar), we could theoretically get 468 watt-hours that month. 

0.26 gpm × 25 feet ÷ 10 derate = 0.65 watts × 720 hrs./mo.
= 468 Wh

So even if there was a nanohydro plant that could harvest that small flow, it would result in less than 1/2 kWh of electricity—per month!—and only 3 cents worth of electricity in Seattle. It’s a tiny fraction of what even an energy-efficient, 6,000-square-foot home would use in a day, not to mention a whole month. 

Would the available energy increase if we weren’t dealing with a constant drizzle? What if, to increase flows to a usable rate, and hopefully increase viable energy production, we could hope that all that rain came in a great deluge of 1 inch per hour (a 100-year storm, in Seattle) over six hours! At that unlikely amount of rain—practically all at once—flow from our example roof would be about 31 gpm. That is a more viable flow rate for hydro turbines on the market and gives us a projected power production of 77.5 watts, but only for those six hours. The total of 465 Wh per month is about the same energy as the drizzly example above (the minor difference is from rounding significant digits). 

This is when inventive thinkers will begin planning for taller homes, or additional rain-collecting roof areas, and tanks to hold the water for release all at once to increase flow. But even that 11,220 gallons of water that falls on our 3,000-square-foot roof that month would weigh almost 47 tons if stored. Imagine a structure at roof level capable of supporting that kind of load just to generate a minuscule amount of energy. And remember, these discouraging energy production numbers are for the rainiest month, in one of America’s rainiest cities. Other months, other places, and smaller houses can only deliver worse performance.

In this case, it would be better to just spend the money on a PV system. To put things into perspective, even in Seattle, which gets only an average of 1.7 peak sun-hours per day in November, an inexpensive (less than $100) 15-watt PV module would make close to the same amount of energy as the proposed rooftop hydro system.

Myth 3: Hydro from Municipal Water Supply

So, a thinking person might begin wondering where they could get good water pressure and adequate flow necessary to run a microhydro turbine. It’s the kind of question an inspired hydro wannabe might ponder, say, while standing in the shower. And that’s when another common hydro scheme is hatched.

Typical municipal water pressure is between 40 and 80 psi, the equivalent of 92 to 185 feet of head. That is definitely enough for a hydro system. And if available flow is about 10 gallons per minute, say at the bathtub faucet, then surely there must be some real power available whenever we turn on our faucets. 

However, if we use our example power formula with a common pressure of 60 psi (138 feet), we get a projected power output of about 138 watts.

138 ft. × 10 gpm ÷ 10 derate = 138 W × 24 hrs.
= 3,312 Wh per day

That 3.3 kWh per day is something—but not a lot. An average American household uses about 30 kWh per day, so would need nine of these units.

For the sake of argument, let’s assume a very energy-efficient home that could run on 3.3 kWh per day. Why not then use such a hydro system? Or, why not offset a portion of a home’s loads with hydro? Every little bit helps, right?

The 3.3 kWh figure is based on using 10 gallons per minute—24 hours per day. That’s 14,400 gallons per day. At an average cost in the United States of $1.50 per 1,000 gallons, that’s $21.60 per day in water costs just to generate 36 cents worth of electricity (based on the U.S. average of $0.11 per kWh). 

Then there is the ecological and moral impact—remember, this is water that has been treated and purified for human consumption, and uses pumps to maintain that pressure—processes likely paid for in part with taxpayer money. Costs aside, what are the implications of pouring good clean water down the drain just to make a little electricity?

Finally, just to add a final coup de grâce to this hydro scheme, remember that most of what we do with our domestic water requires water pressure, as well as flow, to get the job done. Taking the energy out of water to make electricity robs that water of its pressure—water merely falls dead (depleted of energy) out the bottom of a hydro turbine. And pressure at other faucets may be anemic at best—imagine trying to rinse shampoo out of your hair while a hydro system is running full-bore in the same home. Not so effective, or enjoyable.

Myth 4: Reducing Pipe Size to Increase Pressure / Power

There is no substitution for head and flow in an effective microhydro system. When head is inadequate, we begin to think of creative ways to increase pressure. The simple example of watering the garden with a hose comes to mind. Doesn’t putting your thumb partially over the hose opening increase the pressure, shooting water farther across the lawn? What if you use a spray nozzle instead of your thumb? Didn’t you just increase the power of that system by reducing the size of the nozzle? And therefore, couldn’t you increase head (and thus power) in a hydro system by starting off with a large pipe diameter and then reducing the pipe size on the way to the turbine?

Sorry, but no. When a pro measures head in a hydro system, they note two different types. Static head is the pressure at the turbine with the bottom valve closed, and thus no water moving. It is the pressure, from the weight of all the water in the pipe above the turbine. This pressure, measured in pounds per square inch (psi), is in direct proportion to the height of that column of water. For every 2.3 feet of vertical head, you’ll measure 1 psi. Because it is directly proportional, there’s no need to put in pipes and fill them with water to measure it; just measuring the vertical drop between water source and turbine site will give you an accurate static head.

But static head is just a maximum starting point. Dynamic head is the adjusted theoretical pressure in the system when inefficiencies like friction loss of pipes, joints, elbows, and valves are considered. These things hinder the flow of water through the system, and therefore some of its potential energy. Dynamic head is the result of static head minus these power losses, and provides a more accurate estimate of turbine performance.

Adding a smaller pipe section or nozzle is basically adding another restriction in the pipe that creates resistance to the flow of water. It effectively lowers the dynamic head of the system and thus also lowers the total power available in the system.

“Wait,” you say, “what about the hose spraying farther across the yard?” Or maybe you are savvy enough about hydro systems to know that impulse turbines actually use nozzles to shoot a stream of water at the spinning runner. Well, you are right, but neither pressure nor power are being increased by the nozzle. Instead, the existing energy is being concentrated into a smaller point and at higher velocity—which is a more usable form for the turbine—but, in the process, some of that energy is lost to friction.

The purpose of a nozzle is to increase the kinetic energy of the flowing water by increasing its velocity. But this is at the expense of its potential energy in the form of pressure. In fact, on the outlet side of a nozzle, there is no pressure in the water; it is carrying all of its energy in the form of fast-moving kinetic energy. And it is the force of this kinetic energy against the turbine’s runner that makes it spin. But no increase in energy was created. In fact, that water moving faster through a nozzle has more friction loss, reducing our dynamic head and total available power in the system—less power, but in a more useful form.

There is never any more power available than the theoretical maximum based on the initial static head (at a given flow). Every component and change in the form of energy in the system acts as an inefficiency, reducing actual available power. Some of those losses are necessary ones (getting the water down the hill, shooting it at the runner, etc.). Good design can reduce losses, but they can never be eliminated completely. And they definitely can’t be changed to net gains.

Myth 5: In-Flow / No-Head Systems

It’s starting to sound like only those folks with a stream or river on their property have a viable hydro system. But if you do have a good-flowing stream, you’re all set for hydro power, right? Well, it’s even more complicated than that.

We know that the power available to typical hydro turbines is a product of the head (pressure) and flow rate. So we also know that as head decreases, flow must increase to make the same amount of power. But what about folks with a nice river flowing along relatively flat ground? There must be some energy available in that strongly moving mass of water, even though it isn’t falling from a height, right? Well, yes and no.

Besides just turbine size, there are different turbine technologies designed to take advantage of the ratios of head-to-flow at a given hydro site. But as head decreases, the energy gets harder and harder to capture. Reaction turbines, designed for low heads (as low as 2 or 3 feet) spin inside a column of falling water, but need high flow for significant power.

But what about situations with basically no head at all? What about that big river flowing through a flat plain? Well, try putting zero head into our hydro power equation and you will find that, no matter how much flow there is, the power output will be zero, too. To be fair, there must be some head for the water in a stream to be moving at all, and thus there must be some power there to capture. But even though the movement of that flat-water stream looks enticing, there isn’t much potential to start with, compared to the same water dropping down a hillside. And then there’s the challenge in capturing it.

To make up for lack of head, flow would need to be substantial. Either the river must be flowing very fast, and/or a very large area of river must be captured. Both create challenges in the integrity of the mounting structure and turbine runner itself, plus the added danger from river debris. 

A fast-moving river is often only moving fast in the center. Near the banks, shallows, or along the bottom, friction reduces the flow. The speed of the river in the center can’t necessarily be extrapolated to the whole cross-sectional area. Instead, there are specific formulas to account for the reduced flow along the bottom and shallow sides of a stream.

And even a quickly flowing river is moving a lot more slowly than the runner in a jet-driven impulse turbine in a system with higher head. A slowly spinning runner needs to be geared to create the rotational speeds necessary to generate electricity with an alternator. The gearing adds further complexity and friction loss to the system—more inefficiency.

We’re not saying that it can’t be done. But we are saying that it’s unlikely that you can buy anything off the shelf that will do an adequate job for you. There have been, and will continue to be, many inventions intended to capture energy from the flow in a river. These “in-flow” or “current turbine” designs come and go, and come again, but we rarely see anything that performs to a level that warrants a reliable consumer product. There are a couple of in-flow products on the market (Ampair and Jackrabbit) that were originally designed for towing behind sailboats or barges. Some have adapted these to use in streams, but the small swept area of their propeller requires high-velocity flow to make much usable power.

If you are a tinkerer, and enjoy the creative challenge of hydro design, you may be able to fashion an in-flow turbine to make some power (though it may never pay back financially). But if you are being tempted by commercially available in-flow turbine designs, caveat emptor. Do your homework by talking to other reputable hydro installers about your resource and options. Be realistic about your capturable stream area and flow rate. And ask for real-number data, and references, from the turbine manufacturer.

Head & Flow: Check Your Reality

While microhydro power is a reliable and proven technology, often at a reasonable cost, it’s completely dependent on the resources available on a site-by-site basis. Either your site has reasonable hydro potential, or it doesn’t. And it all depends on the quantities of head and flow. There’s no cheating the laws of physics. There is no way to create energy. There is no free lunch.

That doesn’t mean that there aren’t ways to optimize your hydro potential to get the most energy out of your resource. That’s where professional designers and reputable manufacturers come in. They have the knowledge to make decisions on siting and equipment that will maximize the energy made from the head and flow that is available. Intake type, pipe sizing and routing, the size and number of nozzles, runner type, alternator size and type, controller type, and system voltage are all variables that, when combined properly, will make or break your system performance and financial viability.

So give up on the free energy designs. Instead, read some of Home Power’s real-world articles on hydro system design, do a preliminary measurement of your stream’s actual head and flow, and call a reputable microhydro professional. That’s the best scheme for maximizing your hydro system’s performance.


Benjamin Root is no expert on microhydro power, but with 15 years on staff with Home Power, he has seen a frustrating repetition of misconceptions about renewable energy’s potential…and hydro seems to take the brunt. Before you try to debunk Ben’s debunking, he suggests you do the same thorough research that he did to write this article. 

Comments (132)

WhereCanIdeleteMyAccount's picture


Michael Welch's picture
Hi there. It doesn't say that you can't pump water with the wind and store it for microhydro use.

It does say that you cannot do that in a closed loop system, which is not what the El Hierro folks are doing.
WhereCanIdeleteMyAccount's picture


Michael Welch's picture
A closed loop system does not. An example of a closed loop system would be if the wind generators pumped water directly to the hydro generator which then flowed back to the pumps.

What they have on the island is regular pumped storage, where excess wind energy is used to pump water up hill, then when the wind is not blowing sufficiently, the water is allowed to flow downhill through turbines to make up for the lack of wind energy.
WhereCanIdeleteMyAccount's picture


Ben Root's picture
Hi Buuhuu, I checked out this pretty interesting description and assessment of the El Hierro project, just to make sure I knew exactly what you're referring to. http://euanmearns.com/el-hierro-another-model-for-a-sustainable-energy-f... But there is not "room for El Hierro in the description" in the HP article. The HP article is debunking closed-loop systems that are trying to "gain" useful energy without an external energy source. The El Hierro system is wind-energy powered, completely. The Hydro component is, as described in the linked article, "pumped storage". That is, it's using the weight of water, at a height, to store wind energy for use at times of no actual wind input. It is not creating any energy...it's storing wind energy for later. And like all energy storage systems, it is inefficient...there is energy lost pumping water up hill, and there is more energy lost turning that falling water back into electricity later. The island uses the wind energy directly when it can (that's the most efficient), and uses excess wind energy to pump water up hill. When the wind is not blowing, some stored energy can be recaptured, but never as much as it took to pump the water in the first place. There are conflicting reports of just how much backup energy is stored in the system. I think you said 4 days in your initial post, the linked article estimates 12 hours (probably at peak use rates). Either way, once the upper reservoir is empty, only wind energy will fill it again. The hydro component of the system is just an expensive (efficiency speaking) way of storing energy for calm days. None of this is about "opinion". Only physics.
bdmccray's picture

This message is long enough such that it’ll likely be broken up into parts.

Even though this article is several years old, I notice that it still gets replies from time to time and as a practicing engineer, it’s always interesting to me to see the various ways that people try to understand (or outright fight) the concepts involved.

In particular, there are three things that seem to pop up over and over:

1. A lack of understanding of exactly what kinds of numbers are involved. To this end, I thought I’d throw some actual equations in there and show you an example or two.

2. A misunderstanding of pumped storage, since this seems to creep up in the discussion as an example of where the proposed “impossible” system is possible.

3. A lack of a solid understanding of why, even if the pump power is free from solar (or some other source), it’s still not the most efficient way to do this.

(1) Actual Energy Obtained from Hydro

First, let’s look at what kinds of numbers can actually be achieved from a system, since the underlying equation can answer about 90% of all questions as to whether a given hydro setup is even viable.

It takes about 9.81 joules of energy to lift a single kilogram of any substance a height of 1 meter against the earth’s gravitational pull, so we can look at the head of a potential hydro source in terms of stored potential energy using these facts.

We define potential energy as:

PE = mgh

Where PE is potential energy (in joules), m is mass (in kilograms), g is the gravitational constant of 9.81 m/s2, and h is the head (in meters).

However, what we want here is not the potential energy but the available power, which in this case is the first time derivative of potential energy. If we use units of per second, we can make use of the fact that 1 watt is equal to 1 joule/second, and since the water is moving, we’ll use a flow rate (designated as Q) of cubic meters per second (1 cubic meter of water equals 1,000 kg) rather than a static mass in kilograms.

In summary then, we have the available power from a given head of flowing water as P = 1000Qgh

Where P is the available power in watts, Q is the water flow rate in cubic meters per second, g is the gravitational constant of 9.81 m/s2, and h is the head in meters.

As an example, let’s say you have a stream on your property that is 150 feet above your turbine site, and it’s flowing at a rate of 200 gallons per minute. How much electricity can we generate from that?

First, let’s convert these values to their metric equivalents so that we can use the above equation:

1 ft. = 0.3048 meters (exact), so the 150-ft. head equates to 45.72 meters.

1 gallon = 0.00378541 cubic meters, so the flow rate is approximately 0.757082 cubic meters per minute. But we need a flow rate in seconds, so we’ll divide this by 60 to get 0.0126 cubic meters per second.

Plugging this into the equation above, we have:

P = (1000)(0.0126)(9.81)(45.72) = 5651 watts, or about 5.65 kW.

As was pointed out earlier in this thread, the components of this system are not perfectly efficient and because of the small scale of this project, this will be even more the case. Still, we’ll use a 70% efficiency to be optimistic. In that case, the actual power output from the generator will be:

P = (5651 watts)(0.70) = 3956 watts, or about 3.96 kW.

The grid power value of this electricity, given an average rate of $0.10 per kWh, is:

(3.96 kW)($0.10/kWh)(24 h/day)(30 days/month) = $285.12 per month

Note that based upon the above equation, it’s a linear relationship between pump head and power, as well as flow rate and power. This shows you that if you double the head, you double the power, and if you double the flow rate, you double the power. The values above may or may not be realistic for flow rate for a small stream—you’d have to figure out a good methodology to check—but it’s probably a bit too optimistic for head, since few people likely have a 150 foot elevation drop on their property that just happens to have a stream going down it.

This system assumes that you have an actual stream—a free flowing body of water that exists whether you tap energy from it or not. It received its energy through the water cycle—the sun evaporated the water, dropped it back down as rain at a higher elevation (doing the work of putting all that potential energy in the water), and now you reap the benefits for free.

But what about the idea of pumping it back up to the top once it gets back down to the bottom from the turbine. It can’t take that much, can it? Surely, you can salvage at least a little bit of power from it yet? To do this, you build a reservoir at the top of the 150 foot elevation and you install a pump to return all water to the reservoir after it’s left the turbine. What happens then?

While 3.96 kW equating to $285.12 seems like a pretty nice about of electrical power to have from this setup for a month, 200 gallons per minute is quite a bit of water to be pumping through any system on a residential scale, especially to that height. While it’s thousands of times smaller than what goes through the generators of a typical hydroelectric dam, it’s not something that you’re going to get from you garden hose, nor from a low cost pump from your local hardware store. The electricity to power this pump will be substantial.

A typical pump capable of delivering this flow rate at this head will be expensive. For example, given the dynamic head characteristics, TWO of these $4,000 pumps will be required to get both the head and the flow rate required to return the water back to the top of the reservoir:


Given the manufacturer’s specifications (and these specifications are pretty typical for this type of pump), this pump would require 230VAC at 37 amps, so that’s 8.51 kW per pump. Given a rate of $0.10 per kWh, and for two pumps run 24 hours a day for 30 days, that’s $1,225.44 per month to run these pumps. So, to gain $285.12, you’ve spent $1,225.44. And that’s before you’ve spent $8,000 on the pumps. Even if you’re able to find substantially more efficient pumps, turbines and generators, and even if you’re able to reduce all sorts of inefficiencies in the rest of the system, I defy you to find an arrangement in which you will not spend hundreds of dollars a month more than what you get out of the system. If you don’t believe me, you can probably build a much smaller scale version of this arrangement for a few hundred dollars (rather than a few thousand), but the results will be the same. If you increase the head to try to get more electricity, you’ll use more electricity getting the water back up to the reservoir. If you increase the flow rate of the water into the generator to get more electricity, you’ll have to use larger pumps to get that much more water back up to the reservoir. There’s no way to win this battle—the laws of physics will prevail.

I suppose one of the reasons that people initially doubt this is because they underestimate the amount of energy required to lift water in the first place. Most pumps that people encounter in their daily lives are either low head, or low volume (or both). The circulation pump on a home hydronic heating system, the potable water pump in an RV, an irrigation pump used on a farm—these are all pumps that are designed to lift water from a few feet to perhaps a dozen feet, and then their performance drops off markedly. Additionally, most of these pumps have relatively low output volumes—a few gallons per minute to perhaps a dozen gallons per minute. What we need here is something that can pump—continuously—a volume of hundreds of gallons per minute. This is Olympic swimming pool filtration caliber here, and this is not going to be cheap.

Some people reading this may choose to scour online catalogs and hardware stores, and some may claim to find a low cost pump that has both a 150-foot head and a 200-gallon per minute volume, but these are maximums, and the two inversely affect each other. If you look at the manufacturers’ pump curves—the only real way to analyze dynamic performance—you’ll notice that the 150-foot head results in a pump output of only a few gallons per minute, and the 200-gallon per minute output is only good for a pump head of a few feet. There’s no free lunch here because every bit of energy that you’re hoping to get out of that stored water has to have been put into that water, plus the inefficiencies of the pump, the motor and the piping. In short, the laws of physics dictate that you have to put at least as much energy into the water as you’re going to get out of it, and to do this, it’s going to require a very large and powerful pump.

(2) Purpose of Pumped Storage

Given this, what’s the point of “pumped storage”? In short, it comes down to one single thing: Not all electricity costs the same to produce.

Electricity placed on the grid comes from a variety of sources in most parts of the country, and these sources range from nuclear, coal, several different types of gas, hydro, solar and wind. Some of these sources are intermittent, while others are extremely stable. Some of these sources cost a lot of money per kWh to produce, while others are very cheap. Finally, our energy usage patterns don’t exactly match the optimum production times for some of these. For example, some low head and run-of-river hydro plants don’t produce much power during certain seasons because of low rainfall, solar power isn’t there at night, and sometimes wind just doesn’t blow well on certain days. Further complicating this, we demand more power at certain times of day, and during certain seasons, as compared to others.

Our grid is set up in such a way that the power providers manage these intricacies by implementing power in certain patterns based on peak usage and availability. Over the years, it’s been established that the best practice is to leave large, stable sources running for our base load, as well as sources that are difficult to start quickly (such as nuclear). As power needs increase, providers slowly bring on power sources that can be started more rapidly, but at a higher cost (such as gas). This keeps the grid nicely balanced in terms of supply and demand, but not in terms of cost. As a result, it’s desirable for power producers to store power when there’s a cheap excess so that they can use it when there’s an expensive deficit.

Pumped storage is one way to do this. In essence, pumped storage uses excess electricity during slower periods to pump water to a storage location whenever the electricity rates are relatively cheap. Later, when power is in higher demand and becomes more expensive to produce with the peak demand plants, there’s a reservoir with massive potential energy storage that can be tapped to provide the head needed to run the hydro turbines.

Note that there’s no “free” energy here—the process is inefficient, just as it would be at your home. The difference is that for the provider, there can be a difference of 50% or more in generating cost from one time of day to another, so to them (on a massive, terawatt scale), it makes perfect sense to pump billions of gallons of water to recover that energy later. Pumped storage is not an energy creation mechanism—it’s an intentional manipulation of the supply and demand curve to yield a more efficient operating cost for the utility. It’s no different from you buying gas when it’s cheap and selling it when it’s expensive—it’s taking advantage of market forces.

Also, keep in mind that, unlike your proposed residential setup, purpose-built pumped storage plants are designed to a level of efficiency that you simply cannot attain on a residential scale. For example, given the laws of fluid dynamics, you’ll always get much more head loss from your 2, 3 or even 6” pipe for your residential system, while the utility will be using pipes of perhaps hundreds of inches in diameter. The same is true of the turbines, the generators and all other related equipment—they’re all going to be much more efficient components than what you could buy for your home.

(3) Hybrid Designs

The subject of a “hybrid” design has come up in this thread—the idea of using free photovoltaic energy to power the pumps to return the water to the reservoir. Unlike the other proposal, which will fail in a closed loop because it takes more energy to pump water than is generated, this plan will absolutely result in a net positive amount of energy, but at what cost?

The solar capacity costs money—in fact, it’s probably the most expensive source of electrical power right now (even though it’s steadily decreasing). But assuming that someone gave you a multi-kilowatt system capable of running the pump for free, what you’re really doing is wasting this energy because its value exceeds what you’re getting from the water (even though the water is generating power for free).

To get a feel for how this works, let’s review these various arrangements, assuming that you normally use 3000 kWh of energy per month in your home at a rate of $0.10 per kWh. In each case, your electric bill would be:

Straight grid electrical: (3000 kWh used) x ($0.10) = $300

Running stream (described above): (3000 kWh used – 2851.2 kWh from stream) x ($0.10) = $14.88

Pumped storage (described above): (3000 kWh used – 2851.2 kWh from reservoir + 12254 kWh to run pump) x ($0.10) = $1240.32

Photovoltaic “hybrid”: (3000 kWh used – 2851.2 kWh from reservoir + 0 kWh to run pump) x ($0.10) = $14.88

Congratulations—you successfully managed to buy thousands (and perhaps tens of thousands) of dollars in pumping and photovoltaic equipment to pump water to the top of a hill and let it flow back down again so that you could cut your electric bill from $300 down to $14.88. But what if you’d just simply connected that 12254 kWh photovoltaic system to your residence directly, instead of to the pumps? You would not only have NO metered electric usage from the grid, but you’d have a spare 9254 kWh to sell back to the utility. Instead, you chose to waste this 9254 kWh to pump water to the top of a hill just to prove that it could work.

In short, you’re going through a lot of trouble to make something work when what you’re trying to make work isn’t even the most efficient (or financially rewarding) outcome that you’d want. It reminds me of the infamous “Rube Goldberg Machine” concept—a hundred different levers and gears and pulleys and such used to flip a switch, when you could have simply gotten up and flipped the switch. Remember, utilities use pumped storage because on the scale that they operate, and with the peak power cost differentials that they experience, they end up with a net positive. You’re not going to have that advantage because your kWh cost is not going to change whether you operate your pumped storage contraption at 3am or at noon. You’d be spending a lot of money and effort for absolutely no advantage and most likely, you’d be substantially in the hole.

Hope this makes the water a little less muddy. ;-)

- Brian

Chedi's picture

I have read further down the comments now and see the experts have already discussed this scenario. I was thinking for completely off grid home but it would seem the size of such a system required due to efficiency losses and initial outlay don't really stack-up - particularly when compared with an outright solar system with lead battery bank.

Chedi's picture

Thanks for such an interesting read - I feel I understand some of the limitations with hydro power now.

I was wondering though if the closed loop system (cartoon no1?) could be employed as a kind of battery?

I have read about all sorts of exciting developments of different types of new battery technology but it all seems decades away from reaching mass market and thus a price most people can afford.

It seems to me that the lead battery is still king as it is so cheap and widely available and, as with all batteries, need replacing at some point.

Assuming the site allowed for a decent head and flow rate, could a solar panel not power the pump to replenish head with water during the day and hydro used only when there is a high demand for power?

I'm thinking a residential scenario where solar panels are used for low voltage requirements such as lighting, computers etc and the hydro for when more 'grunt' is needed i.e. Microwave oven, washing machine etc

Anyone have any thoughts on this?

ppz1961's picture

Hello Benjamin,
I found your article (thx to google) and enjoyed (...) the long fight between readers.
I understand the X laws of thermodynamics, so no nightmare posts here.
But I have a question of feasibility. Is it possible to use a small chinese microhydrogenerator (12v, about 5-8 watts) hooked to my main water (3/4" npt) to trickle charge a small battery ?
The purpose: the battery will provide power to a 12V valve relay for 2-3 seconds, once in a while. So no big use, not a big battery, just a small amount in case of... But I need to keep the battery fully charged (or at least sufficiently charged). Is it possible with such hydrogenerator ?
Thank you

Grey's picture

Hello Michael or Ben,

I am doing some research on ways to deal with rain water in cities for a geography project, and I was considering the possibility to use rain water running through drainpipes of buildings to generate energy. However, you have shown that it only generates a very small amount of energy when used in a domestic situation. Now I was wondering if this would be different if it concerns a tall building (such as a flat or skyscraper) instead of a normal house? As the head will be a few factors greater and the roof surface that the rain falls on is likely be larger too, may this be (at least slightly) cost-efficient? I'm already a bit doubtful after seeing the very small amount of power generated by the Seattle mansion, but I'd like to know for sure (and I'm not very skilled in physics so I'd probably fail when trying to calculate it myself)
Thank you in advance!

Grey's picture

Ok, I already made an attempt on calculating it for the city of Rotterdam (the city my project is about).

I took an average head of the tallest buildings in Rotterdam, which was about 105m (= 344 ft)
Then I found a random ground surface of one of the buildings which was 68.000m2 divided over 44 floors, which means a roof surface of 1568m.
I found that it is estimated to rain 850mm on average in a year in the Netherlands in 2020, which is 850 L/m and on my ground surface it means there is 1,33 x10^6 L of water/year (=3,52 gallons/year)
I calculated this was about 0,67 gallons/minute, and using the formula on your website I calculated that 344x0,67/12 = 19,2 W and 460 Wh in a day.
Are these outcomes correct? (still very doubtful about my calculations) And if yes, what would this mean practically? What appliances could run on this amount of power? (I understand that the supply is not very stable as it is dependent on the rainfall, but I guess every bit helps)

Grey's picture

I checked around a bit and it seems I can power exactly one lightbulb in my flat... which is not a lot. I guess I'll just stick to my other ideas for reusing rain water :)

Ben Root's picture
Yea, not a lot for a 44 floor building. And that's dependent on a steady rain 24/365. I hope the Netherlands isn't quite like that. Of course, twice the rain at half the time doesn't really change the totals anyway.
Ben Root's picture
Hi Grey, it's all about scale. We've given you the math to answer this question for any size/height building in any climate...try the math for yourself. Just remember that head and flow are both necessary; the tallest building won't make up for the low amount of flow (volume) that a building area can capture. Is there "something" there? Yes! Is it economically viable to implement? Unlikely. For example, one of the largest buildings (in area) in the World is the Boeing factory in Everett, Washington (100 feet tall, and has similar rainfall to Seattle). But even that is only about 100 acres of collector area...not really enough to create a viable "stream", and even if you did harvest what was there, it wouldn't put much of a dent into the energy use of a jet-airplane factory.
Grey's picture

Thanks for your answer! I have just made a calculation, would you mind looking at it to see if it's correct and if the amount of energy I would theoretically receive would mean anything?

Swaspes's picture

Hi Micheal or Ben

I have read through all the info you have given and I am a complete idiot when it comes to power.

Let me start from by sketching my problem and maybe you can advice accordingly.

I am living in Namibia Africa on the banks of the Kavango River. I am currently building a aquaculture farm on a 12 hactar plot about 55km outside a town called Rundu if you wish to google it. We have a stable economy but due to exchange rates solar systems are extremely expensive in Namibia. A 20kva system cost approximately N$1,200,000.00. Which would be my approximate required electricity for day to day running of pumps for fishponds and irrigation of crops. To install a gov gird system due to the location would cost in the region of N$3,000,000.00.

Like I said I am situated on the Kavango river although it is a fairly large river it is flat and does not flow very fast. Now I have the basic picture of efficiency and understand from the article my predicament.

I were contemplating to install a hydro system by means of pumping water in to 5m high reservoirs and to generate electricity using the water flow from there back into the river. Now I know that this will not be very efficient from the article above but some electricity is still better then non.

The idea I had was that I can get a pump that can pump enough water that use minimal electricity. ( There are pumps like this available on the market ) and to use pulley systems from the turbine to turn the generator. (like a cars gearbox, were by you use the same amount of power but your momentum and speed increases) Basically almost newtons 3rd law of leverage.

I rely need a cost effective solution as I am currently paying the start up of the project out of my salary and in the end the project aims to start a training center for the local community to help them become some what self sustaining as currently they can only plant crops during raining season, which is 3 months/ the year and further they are relying on fish form the river for sustenance and as in all parts of the world over fishing is becoming a major problem.

Michael Welch's picture
No matter what you do, your pump will use more electrical energy than you can get back out of the pumped water by running it through a hydro plant. That translates to a net loss, which won't help you one bit.

Your only real hydro choice is an in-stream undershot paddle-wheel setup. There are very few commercially made units out there. Try an internet search to see what's available.
Swaspes's picture

Hi Micheal

I it posible to build it my self and if were could I find some plans on it



Michael Welch's picture
I think most are homemade. Use your favorite internet search engine to find plans. And note that there is a Yahoo group called "microhydro" that is full of hydro experts who can be helpful: microhydro-subscribe@yahoogroups.com
Scott300's picture

Hello I am new to the site and new to the entire engineering of any of this, with that said, I have a question about the processes of generating usable power from the systems listed. I have considered the process of hydro power to run an electric pump to cycle water from one container to another lower to higher and came up with the same conclusion as stated, I have recently seen someone using a RAM pump to move water at a steady and reliable pressure for storage as a fresh water supply. My question is using a RAM pump, or series there of, in various sizes as dictated by necessary flow (head) in an enclosed system a viable way to function a micro hydro power station sufficient to charge a battery bank? Don't bash, don't hate; remember newbie. Thanks

Michael Welch's picture
No, it would not make sense to add a ram pump into the system. A ram pump requires head and flow to operate, as does a hydro turbine. So instead of adding the inefficiency of a ram pump, why not just use that original head and flow to make electricity with the hydro plant?
Scott300's picture

Thanks for the reply, I was starting to think that this thread was not being viewed anymore. My thought was to move the water to a higher location and use the drop from that location through a power plant. I started looking at the numbers for flow and realized that I couldn't move the water in a sufficient amount to retain flow into the power plant to retain the head necessary there would be more out flow than the pump could pump in.

Michael Welch's picture
Efficiency rules. Say your hydro plant is 60% efficient at converting water power to electrical energy. If you first use a ram pump at about 75% efficiency, you've just changed your system efficiency from 60% to 45%. So you get a pretty big loss by increasing your height.
BigJohnFRC's picture

So is it possible to charge batteries with a closed loop system and use that power later to be able to stop the electric bill from growing even for one day of the month? Or will the generator create only enough electricity to power the pump to move the water to turn the turbine to turn the generator to create electricity? Will the generator only create as much electricity as the pump needs to run and push the water through the system? Will the generator even create enough power to run the pump at all?

Ben Root's picture
"Will the generator even create enough power to run the pump at all?" NO, power will NOT be created, nothing will run at all. And just like the original article says, the tendency is to try to add more components/steps/process (like batteries) to "trick" the system into working. But really, each additional conversion step is actually reducing system efficiency and getting further away from an efficient transfer of energy. The best thing to do is to have the simplest and most-efficient system (did you read my response about hooking the generator directly to the motor...that's about as simple as you can get). But even that wont work, because these are energy transfer systems: They need energy "in" to get energy (a little less) "out." If you're not actually putting energy in, you wont get anything out. There is no magic in the gizmos themselves.
Ian Woofenden's picture
Hi John,

It is not possible to end up with any energy in the closed loop system you describe.

Adding batteries adds even another inefficiency, because for every 10 kWh you put in, you get out about 8 kWh.

Find a real hydro source -- continuously flowing water falling down a hill, provided by nature. Then you'll really have some energy to work and play with!

And take a look at solar electricity, a renewable energy technology that taps a resource available to many more people than hydro.


Ian Woofenden, Home Power senior editor
BigJohnFRC's picture

So how is it that if I power my generator with a gas or diesel engine the generator will have enough electrical output to power my entire home with electricity, but if I power it with water pushed by a water pump in a closed loop system the generator will only have an output of enough electricity to run the water pump and and as you say, the output will slowly diminish to a point that it won't even power the water pump?

Ben Root's picture
As long as everyone is still having fun with this discussion, we can keep playing. You can power your house with a gasoline-powered generator because there is energy in the gasoline. Some of it gets converted to electricity, some of it gets wasted. But in a closed loop hydro contraption, there is no energy source to "power" it to start with. You will get "no" energy out of the system, because no energy is going in to the system. Energy is not created by a generator, it is "moved".
Ian Woofenden's picture

The answer to your question is that you are not trying to make more gasoline than you started with with your generator.

You are continuously feeding fuel into the generator, and you are accepting the substantial losses as a "cost of doing business" in the gas generator world. Google the efficiency of your gas generator, and you'll see that you get out in electricity a fraction of the potential energy in the gasoline you put in. Then apply that principle to your closed loop hydro fantasy.


Ian Woofenden, Home Power senior editor, and font of endless patience and good humor ;-)
BigJohnFRC's picture

I'm simply asking why is it my generator being run on diesel will produce enough electricity to power my entire home but if I run it on water pushed through a closed system by a water pump it won't create enough electricity to even run the pump as you say?

1. Run generator on diesel and get enough electricity to power entire home.
2. Run generator with a water pump and it will not even produce enough electricity to keep the pump running.

Why is that???

Ian Woofenden's picture

I'm not sure how many ways to say this: you do not have an energy SOURCE.

Your fuel-fired generator has a regular input of fuel. Your closed loop hydro fantasy has no energy source.

Imagine a hand-crank generator. We can make electricity by turning the crank. When we stop turning -- no more fuel -- we stop generating. We could wire that generator's output to a motor to turn the crank, but the losses in all parts of the system would leave us in the same position -- stop turning the crank by hand and there is no energy source.

Whatever you start with on the input of any energy system will be the most energy you ever see -- it's all losses from there on, regardless of the source. So you always need to generate more than you will actually use, to accommodate the losses. You COULD run a "generator with a water pump", but you would need to continuously power the pump with some outside source of energy greater than the generator's draw. And you'd be better off just using that outside source directly, bypassing the losses of the pump and generator...

Now I have a question for you: Have you ever seen such a system as you propose working?


Ian Woofenden, Home Power senior editor
Michael Welch's picture
This is already answered, see above.
Ben Root's picture
Hey all you free-energy dreamers...here's a little conceptual reminder to help you let go of your closed-loop hydro system fantasies: Remember, a closed loop hydro system is basically the same as connecting an alternator directly to a motor (wires to wires ,and shaft to shaft) and expecting energy to be produced. In the hydro model, you're just replacing the shaft to shaft connection with a pump impeller, water pipe, water, and turbine runner. You can imagine all the friction losses in those elements, so why not just get rid of them and connect the motor and alternator shaft to shaft? Here's the deal, neither a motor nor an alternator create energy; they just pass energy through them from one form to another. An alternator turns rotational energy into electrical energy; a motor turns electrical energy into rotational energy. Now even if both the alternator and the motor were "very" efficient, they still loose energy in that conversion process. For the amount of electrical energy that gets put into a motor, less rotational energy comes out. And the same is true for an alternator, whatever amount of rotational energy that gets put into it, less electrical energy comes out. Hook the two together and nothing will happen. Nothing. Now, if you give then a spin to get them started, you could measure electrical energy in the circuit at that moment, but it would be less than the energy you introduced with the spin. And that electricity would not help the system keep spinning. Why? Electrons move a the speed of light, that's pretty fast for the compounding inefficiencies to bog the system to a standstill. It takes energy (electrical) to spin a motor, and the larger the mechanical load on the motor the more electrical energy it takes to spin it...that makes sense to most of us. But remember, it also takes takes energy (mechanical) to spin an alternator, and it takes more mechanical energy to spin an alternator when a larger electrical load is put on it. Really...an unloaded alternator spins almost freely, but turn on a light bulb and you can actually feel the alternator get harder to turn; two light bulbs, even harder. So in the case where your alternator is attached directly to your motor, the inefficiencies (no matter how "minor") of both units make the motor load too big for the alternator to overcome, and the alternator load too big for the motor to overcome. The system is bogged down by its self. You would need an external energy source to make this system work at all. And that's the clincher, if you DO have an external energy source, just use that. If it's a mechanical energy source (like falling water) and you need electricity, use an alternator (connected to a hydro turbine). If it's an electrical resource and you need rotational mechanical energy, use a motor. In either case you'll waste some of the energy in the conversion, but you'll get it into the form you can use. If you have an external energy source that's electrical (liket he utility grid) and electricity is what you need, just use the electricity. Don't wast some of it making a motor and an alternator (not to mention a pipe full of water) go around in a circle... You can't change forms of energy back and forth and expect to "gain" anything...that's just wasting energy in the inefficiencies of conversion.
BigJohnFRC's picture

Let's say I build a closed loop system.
Reservoir - 1,000 GPM pump - water chamber for turbine blades to be in - return line to reservoir. And of course the turbine runs a generator that produces electricity.
Consider that I am also On-Grid.
If I use my On-Grid electricity only to run the pump on said closed loop system and use my On-Grid electricity to occasionally run more water into my reservoir from my garden hose to replace loss of water to evaporation. And then use the generated electricity from said closed loop system to run everything else in my household would my electric bill not go down?

Lothorian's picture

Do it, it will work. Ben gets paid to tell everyone NO. Your idea above works, There are 14 closed loop pumped storage facilities in America and 120 more around the world. These FACTS are public through .gov docs look them up. BigJohnFRC my entire company is based around a closed loop pumped storage power plant as well as using solar power to offset the efficiency drop in mechanical devices. Flowing water is energy and Archimedes showed us this 2500 years ago with his grain mills at Barbegal.

BigJohnFRC's picture

Thanks Lothorian. What is this crap where people purposely try to lie to you and the more you try to get them to fully explain their theory the less they can because you beat down all their commotion of bullshit that is meant to distract you from what the real topic is. They dance around giving you an answer that makes no sense forever. Finally they say you will just have to go try it and see it fail because they can't tell you why it will fail because it doesn't fail.
These kind of people are what is wrong with the world today. When my comments and questions finally exhausted all his misdirection and bullshit he quit responding because I had him down to the brass tacks and his back against the wall.
They actually tried to say that by running water with a pump that is powered by the generator in the closed loop system the water and pump are both part of, you would not create enough power to operate the pump in the system so you certainly would not create any power for use outside the closed loop system. Hell, they even said you would run out of power because the generator couldn't supply enough power to run the pump. A generator that won't power a water pump. Hmmm. LOL. Biggest water pump in the world and smallest generator in the world I guess.
Thanks again Lothorian. :)

Foxy T's picture

Wow, I've been watching this thread...and snickering to myself. But now, with the "lies" and "bullshit" accusations, I feel like piping up. You know that those guys at Home Power are humans, not robots, and they're taking their time and energy to politely explain to you the simple concept that you're missing. And because they're pros, they're trying to be polite to you while you're getting all aggressive and accusatory. Well, dude, thinking outside the box is all great, but do you really think you're the first person to come up with this idea? Are you the Einstein of hydro power who's going to save the world from the government suppression of free energy with your great new idea? I'm sure you're not the first. In fact that's probably why they had to write that article in the first place...too many loons like you who don't understand basic physics asking this same stupid question over and over. If a scheme like yours would work, don't you think one of the hydro pros in the decades history of the technology would have done it already? Actual people who actually understand hydro, with boots in the stream and wires in hand, would have tried it (not just arm-chair keyboard dreamers getting all creative). How come all of a sudden you are the messiah of hydro brilliance? There are many small-scale hydro equipment suppliers in the world (many advertise in Home Power) and I dare you to call them and ask about a system that would do what you propose. You'll get laughed off the phone (actually, they'll probably try to politely explain physics to you too, at least until you get rude to them).
Here's one for you, so you are going to make sure the generator is big enough to power the pump (like oversize it a little, right). So now you have to oversize the pump to move enough water to spin the bigger generator, right? So now you better make the generator even bigger. No wait, bigger pump. Duh. Have fun, sucker.

Lothorian's picture
Michael Welch's picture
Caution, readers, but this is just flat out false info. I caution anyone reading this to be sure to double check what is possible before believing that one can break the laws of physics.
Ian Woofenden's picture
It's a misconception that water coming out of a well-designed hydro turbine is "under the same...pressure". The goal of a hydro turbine in most cases is to remove all the energy, and that means the water is "dead" -- at atmospheric pressure.

There is only so much energy in any particular head and flow combination. After you've tapped it, you start over from scratch. This is a unique characteristic of the hydro resource. With sunshine, we can just add another PV or solar collector. With wind, we can add another or a larger wind turbine. With hydro, we have a certain amount of energy, and it's usually most cost effective to tap it with one turbine. If we use more than one, we won't get any more energy than is there.


Ian Woofenden, Home Power senior editor
Ben Root's picture
Michael is correct. The point/purpose of pumped-storage is "storage"; saving energy available now to use later. And just like batteries, you get less energy out than you put in. There has to be a reason why using it later is better than using it now, and that reason has to out-weigh the losses of the storage method. I think that if you reread John's idea, it's not about storage, but about perpetual-motion free-energy generation. if that worked with hydro loops, it would have been working 100 years ago, and everyone (including me) would already have one in their utility room...no need for coal, oil, nuke, natural gas, solar, utility grid, or anything else...build a little one and put it in your pocket to charge your cell phone. But...Sorry. And the amount I get paid in my life is nowhere enough to convince me to mislead the world about sources of clean energy. On the contrary, my goal is to help educate people, all people, about their options to get away from dirty and corporate-controlled energy sources.
Michael Welch's picture
Of course pumped storage works. But every single one of those pumped storage facilities use more energy to pump than they get back out through hydro generation.

Energy gain is not the point of utility-scale pumped storage, but the point is to use excess energy off-peak to pump, so that energy can be produced on-peak.
Ben Root's picture
Adding complexity to a system is never an efficiency gain. Each conversion step creates a loss: remember nothing is 100% efficient. So even if your turbine is 90% efficient, and your generator is 90% efficient, and your piping friction losses are only 10%...that's 0.9 x 0.9 x 0.9 = 0.73...73%. So that's spending 27% of your grid electricity just to make water go around in a loop. Nothing is gained; 27% is wasted. Your electric bill will go up 27% and the "hydro" system will cost money to buy in the first place. You'd be better off building a yard-art water-wheel fountain...at least you'd get the pleasure of watching it go around.
BigJohnFRC's picture

So you're saying that the hydro system I've created in this idea will create no electricity whatsoever? Not even to cover the 27% you mention I'm losing? You said my electric bill will go up 27%. I mentioned using my grid electric for nothing but running the pump and refilling the reservoir and stop using it for anything else at all such as my entire homes electrical use and let the hydro system I created pay for all of my homes electrical use.
You say I'll make my bill go up 27% and that is all that will happen. Why won't my hydro system create any electricity which is what you seem to be saying?

Ben Root's picture
Yes, that is basically what I'm saying. But the 27% was just a simple example in the moment of writing back to you. Reread the article myth #1 where we ran the numbers a bit ore accurately, and the answer for the hydro loop efficiency was more like 41%, meaning a 59% loss every time around the loop. Will your hydro "make" power? No, it will USE power: 59% of the power from the grid will be used to run the hydro system, and 41% will be passed through the hydro turbine on to your house loads. It will "seem "like you're getting energy from your hydro, but it will be 59% less energy than you are using from the grid to make the whole process work. You will get more energy from the grid by just using grid energy directly, and not bothering to run water around a loop, spin a turbine, convert energy to electricity, convert it back to motion to move water again.
BigJohnFRC's picture

I've got to make sure I'm understanding you correctly.

1. Let's say I have a $406.00 electric bill this month. Which I actually do have. And that is the bill for this month for having my power company supply my entire home and ranch with electricity.

2. Now let's say I disconnect everything from the grid except the pump that pushes the water through my home made system. Remember my system has a reservoir and a pump that pumps that water through a chamber that turns my turbine which turns my generator which creates electricity. After the water turns the generator that same water returns to the reservoir to be pumped through the system over and over again.

3. Along with the pump being on the grid I also have my water well pump connected to the grid to refill the reservoir on my home made system very infrequently due to evaporation. So it's just the pump in the system and my water well pump that are connected to the grid now and nothing else on my entire ranch and home are on the grid.

4. It seems to me that you are saying that when I'm set up like this I am wasting the power I use off the grid to run the pump in the system, and the pump on my water well very infrequently to refill the reservoir due to evaporation. And you say I'm wasting that power because the generator in my system will not create any power for my ranch.

5. How is it that turning this generator will create zero useful power for my ranch? Why is there such a thing as a generator if when you turn it nothing is produced and you are simply turning it for the joy of watching it turn?

Ian Woofenden's picture

It's simply a matter of efficiency. Every power generation/conversion operation entails a loss. If you start with a certain amount of hydro potential, there will be less and less as the water works its way through the system. And when you start by _paying_ for the energy to lift the water, you will yield less and less energy and benefit at every step in the process.

You will never generate as much from your proposed hydro system as you use in the pump. This sort of system yields a net LOSS, not a gain.

There is energy in falling water. But it's not free energy if you pay/use energy to get the water to the top of the run.

The "free lunch" is with naturally occurring pressure and flow. If you are supplying/paying for the base energy, there's no free lunch.


Ian Woofenden, Home Power senior editor.
Michael Welch's picture
Let's try this from a slightly different angle. Say your entire farm needs and uses 1000 watts of power constantly (an arbitrary number for demonstration). Right now, all of that is being supplied by the utility.

But if you decided to run your farm off of a hydro power plant that is supplied by a pump, you will find that due to the hydro plant's inefficiency, it will need to have about 20% more power in the water coming to it. So that means the pump that supplies it will have to provide 120% of the power that your farm uses, or the water power equivalent of 1,200 watts.

But also, the pump is not 100% efficient (let's give it 90% efficiency) so in order to provide that 1,200 watts of water power, it will need 0.9 x 1,200 = 1,333 W of electrical power which comes from the utility.

So all of a sudden, you have gone from needing 1,000 W of power from the utility to run your farm, to now using 1,333 W of utility power to do the same thing.
BigJohnFRC's picture

So you are saying if the only electricity I use from the grid/utility is to run the pump, then that electricity would cost me so much that it would cost me even more to leave the grid and run my system than just staying on the grid?

How can running that pump cost $406.00, or as you say even more than $406.00 which is my current electric bill amount?

Also consider that once the pump is running and the water is turning the turbine and the turbine is turning the generator and the generator is creating power, I will then flip the switch and run the pump off of the generator. So I only use grid electricity to get the pump going and then run it off the generator once the generator is creating power.

So, I use grid power for 5 seconds to start the pump and then use the power created by my closed loop system to power the pump and my home and ranch and somehow that 5 seconds of grid power will cost me more than I'm paying for the whole month of power to operate my home and ranch?

Are you saying that I would have to have such a huge pump, turbine, and generator that the 5 seconds of grid power I use to get it running would cost more than my entire monthly power bill or are you saying my generator will create no power?

Michael Welch's picture
The pump will not run for 5 seconds, it will run constantly because it supplies all the water power that the hydro plant uses.

I agree with Ian, I think you should try it and report back. Sometimes the only way to learn is by doing.
Ian Woofenden's picture
Hi John,

You seem to be running on multiple misconceptions.

If you start with $X worth of pumping energy, the output of the closed-loop system you describe will be $X - $Y, where Y is the (several) losses in the system. It will never generate as much energy as you put into it. And it will not be self-perpetuating or free.

ALL of the energy in your proposed system comes from the original pump. There is no natural energy involved, as far as I can tell. Hydro-electric systems are amazing because the source energy is free and naturally occurring. You energy is created by your original pump (which you are paying to power). It is quite similar to trying to make wind energy with a turbine given wind by a gasoline-powered vehicle or electric fan.

If you don't believe us, I encourage you to try it, and report back.


Ian Woofenden, Home Power senior editor
BigJohnFRC's picture

It's not that I don't believe you. It's that I'm trying to make sense of what you are saying.

Let's try this scenario.

I build my home and ranch out in the wilderness where there is no electrical grid.

I build my closed loop system out in the wilderness on my ranch where there is no electrical grid.

I start my pump to move the water through my closed loop system with a diesel motor.

As soon as the generator on my closed loop system is producing power, I turn off the diesel motor and run the pump off the power the generator is producing. So, I used the diesel motor for 30 seconds to start my closed loop system then shut off the diesel motor and ran the pump off of my closed loop system.

Are you saying that once I've done the above, and my closed loop system is running itself, I will get no power whatsoever off of my generator? Or the power I produce will be totally used up to run the pump? Or what?

And let's add to that a need to run a well pump to replenish water in the closed loop system once in a great while due to evaporation. Although it is totally enclosed so I don't know where it would evaporate to. But some does evaporate over time so I simply run that well pump to replace water that evaporated off of the closed loop system.

Maybe the cost of my pump, turbine, generator, return water line to my reservoir tank and reservoir tank will be enormous I do not know, but let's say I get all that for free and I have the closed loop system running with a 1,000 GPM pump and a huge turbine and a huge generator and an endless supply of water in the reservoir. Are you saying I can't get a generator big enough to run that pump or that running the pump takes more electricity than my generator can produce or what?

I don't understand how a generator running on this closed loop system will not create electricity or how running that pump off this closed loop system will take all the power that the generator can produce so there is no more power left that I can use to run things in my home or on my ranch.

Ian Woofenden's picture
Hi John,

All three of us are trying to explain, but we "can't understand it for you". Your basic idea of a "closed loop hydro system" is flawed. It will not work. At every step in your process, there are losses -- pipeline up, intake, pipeline down, turbine, generator. If you start with 500 watts of input, you will end up with significantly less output. If it ran at all, the losses would very quickly drag the system to a halt.

It's not magic, or naysaying -- it's just math and physics.

The true magic is _renewable_ energy, which just keeps coming freely. Every time you need to have paid input, you are starting with a loss, and the natural losses will kill the project.

Pumped storage, as Michael notes, only works because there is an enormous surplus that would otherwise be wasted. It is not a "closed loop", but a way to recoup some of the lost energy for use in times of need. The hydro dams MUST have much more surplus electrical energy than they need to cover the loses in pumping, piping, generation, and transmission.

But in the end, if we can't convince you, we do encourage you to try it, and/or find a real world example of what you have in your head actually _working_. It's really easy to say words -- nice or nasty -- on a page. It's harder to show what you are talking about in real life. Our magazine regularly profiles real renewable energy systems producing real energy. If you can turn your belief and dream into action, we will be happy to look and listen.


Ian Woofenden, Home Power senior editor
Michael Welch's picture
It will generate electricity, but always less than the amount of energy it took to pump.
Akkad's picture

:( my two cents...

I admit I am not an inventor or a scientist and feel totally out of my place here. Also clearly after reading this article I felt totally crushed as I am one of those dreamers in free energy.

However, I must keep trying and beg of you and the readers to see my idea and my only addition to the possibility here is that I want to use many nano turbines every 2 meters or so, say in the fall of 30 meters high building. And all of their energy output is collected in one battery plus the help of solar and wind and the back rotation of the turbine blades to actually help the water up again. In the pic it shows basins for the water but I think a closed sealed rotation is best and maybe oil instead of water. More like our blood flow but with many hearts instead of one.

Michael Welch's picture
Each turbine in series removes a little energy from the water. Ask yourself, where is the energy going to come from to raise the water back up to start the process over again?

If by some miracle (and defying the natural laws would be miraculous), you could get as much energy out of the system to put back into it (which you cannot), where would useful energy then come from? You would have to get more energy out than you put in so you can have some left over to do work.

Sorry to say that there is no way to get as much energy out of any closed system as is put into it. This has been a truth forever. Many people have wished it was different, but it never is. There is no such thing as free energy.
BigJohnFRC's picture

I'll try to make this as simple as possible.

I have a large tank of water which is my reservoir. Attached to the bottom of the tank is a 1,000 gallon per minute water pump that takes water from the tank and pushes it to a chamber that the turbine impeller is in and turns the turbine impeller which in turn turns the generator which produces electricity. the water goes right through the chamber with the turbine impeller in it and then runs through a return line to the large tank, my reservoir, and starts the whole process over again. Thus a closed loop system.

I start the pump with a diesel motor and as soon as the generator is running and producing electricity I shut off the diesel motor and let the generator run the pump. So I used the diesel generator for 5 seconds to get the closed loop system running and having the generator run the pump which maybe took a cup of diesel fuel to accomplish. There is no other outside source of power other than the diesel motor and I only need it to run for 5 seconds to get the system going and then let the system run itself.

So, are you telling me that the generator will only produce enough electricity to run the water pump in the system and there will be absolutely no more electricity created that I can even run even one light bulb on in my house above and beyond running the pump that runs the system? Are you saying that the generator will only create enough electricity to run the pump that runs the turbine that runs the generator and not create any more electricity for me to run even one light bulb? If that is true then what is the point of having a generator?

Akkad's picture


Thank you Mr. Welch.

I will not give up though. They say there is one born every second. :).

For some reason my link was not published.

It's in a Facebook page called AKKADEMY

billdsd's picture

What about using solar or wind power to power the pump? I agree that powering the pump off of the hydro power that it's causing to be produced makes no sense but storing power from an external source would. This would allow the storage of excess power during the day for solar or during windy times with wind and use it as hydro when those aren't available. I'm not sure if maybe it doesn't work so well on a small scale.

This is done on a large scale. I can't find anything on it be

Ben Root's picture
Hi Billdsd, We're not trying to gang up on you; these are exactly the kinds of questions we're trying to answer with this article. Yes, utility-scale hydro plants sometimes pump water uphill, but nothing is ever "gained" by doing so. The purpose is to help balance the fact that bringing turbines up or down is too slow/cumbersome to keep up with fluctuating load demands on the grid. Basically, they are letting their turbines run, and are load-balancing with the pumps. Nothing is gained, but less energy is lost than just "dumping" it. Your private, residential-scale solar or wind system would never be large enough to challenge the grid's ability to receive your excess energy...just bank your excess with them. If however, you are talking about an off-grid PV or wind system, then you sure may have excess energy sometimes. Ideally, the goal is to find ways of using that energy then and there (do laundry when the sun shines). But if you do need to store the excess, then batteries are far more efficient (even at 80% for flooded lead acid) and less expensive, than adding a hydro/pump system with the multiplied inefficiencies for both legs (pump and turbine, pipe, etc.) of the system. Either way you'll be wasting some, but batteries will waste less. Remember, in no case is adding additional system complexity ever gaining energy.
Michael Welch's picture
There are reasons why it is not done on a small scale: First, it takes a lot of storage space. Second, pumped storage is a lot less efficient than storing that solar or wind in batteries.
Ian Woofenden's picture
Hi billdsd,
It is done on a large scale, where there is LOTS of surplus energy to burn -- in big hydro dams. It's certainly possible on a smaller scale, but it's doubtful that it would be cost effective. Most solar- and wind-electric systems are connected to the grid, and get 100% credit (and some even get payment) for any surplus. So it's usually not "waste" anyway.
And even if it is waste, the cost of set-up would probably outweigh the benefit. Certainly setting up a system dedicated to doing this would be wasted money, since you are back in the realm of paying for the original energy, after which it's all "cost" -- losses associated with the system.
Though there are exceptions to every rule, hydro makes sense when there is a natural, free, and abundant flow, and doesn't make sense if you have to pay for the energy to create the flow.
Regards, Ian Woofenden, Home Power senior editor
tjdm1980's picture

Thanks so much for the replies. What about Sky Green's claim

"4. The water is then recycled to proved power to the generator.
5. Water is directed into the reservoir using a pump powered by the generator." ecowatch-dot-com/2015/09/11/sky-greens-vertical-farm/

I'd love anyone help me get a similar open sourced system, if viable.

Michael Welch's picture
I doubt if his system even exists as stated. Please pay attention, Ian and I are experienced in the realities of these systems. A wise person would carefully take a look at what we are saying. And if you do open your mind to what we've been telling you, you will likely leave this idea behind, and move on to other things.
tjdm1980's picture

Hi there. Can I get your thoughts please: Let's say you have a homestead hydroponics, aquaponics, pond, etc. closed loop hydro system, all components are properly connected to let gravity power flow direction. Circulated by a water pump. Will 3 or 4 household/mini waterwheel power generators in between each component's drop in height make it beneficial to a hybrid renewable power collection system i.e. wind, water, solar? Problems foreseen, any benefits? Thanks much

Ian Woofenden's picture
Hi tjdm, Re-read Myth #1, and consider that in your scenario, all the original energy in the moving water comes from the pump -- without the pump, nothing would happen, right? So the actual source of any energy in the system is the electricity used to run the pump. You must pay for the electricity, and anything that makes energy from that moving water will require more electricity, because it is slowing down the water flow, and will require more payment for more energy. Hydro-electric systems are amazing because they tap a free, abundant, and recurring source of falling water. If you don't have a stream or spring falling down a hill, you simply do not have a hydro source. Trying to make one up is very much like trying to get solar energy from a light bulb in your basement. While you could get a little tiny bit of electricity from a solar cell set in front of that light bulb, you'd have to make or buy much more electricity to run the light bulb. Regards, Ian Woofenden Home Power Senior Editor
tjdm1980's picture

Thanks for the reply. Use solar to initially power the pump. Doesn't gravity give the water potential power that can be used multiple times in a hydro system with varying heights? What about using a bell siphon setup to power a waterwheel? Is more energy produced by the siphon effect?

Ian Woofenden's picture
Hi tjdm,
Using a solar-electric array is a great way to power a pump (or anything else). But as soon as you try to generate energy from the flowing water, you are starting down the highway of losses. There is no magic that can get more energy out of your solar array -- when you run a pump with it, there will be a loss; when you push water through a pipe, there will be a loss; when you generate electricity with a hydro turbine, there will be a loss. In the end, you'll have much less energy than you started with from your solar-electric array. So why not just use solar energy?
Sure, there is energy in gravity-fed water. But how did the water get there? Did you have to spend $ or effort to get it up to the top of the hill? If so, it's not "free". The amazing thing about hydro-electric systems is that _nature_ takes the water to the top of the hill, with no cost, so the losses inherent in a system are unimportant.
A siphon takes energy to start, and there are losses inherent in any piping system. If you are talking about a siphon to overcome a hump in the landscape that will mean you can then run water _naturally_ down hill a long way, it might be worth doing. But if you're thinking of siphoning up to run back down to where you started - nope. What you need to be looking for is _naturally_ falling water. All other schemes will not make sense, unless you have an enormous amount of energy to waste for some reason.
Ian Woofenden, Home Power Senior Editor
tjdm1980's picture

I am looking at it from the perspective of already needing to pump the water to the top of a closed loop hydro system in an aquaponics or hydroponics setup, multiple systems in a homestead connected together. If I have to do it anyway, are there benefits in adding the hydro power wheel, or is it a waste of time and money in your opinion? Thanks...

Michael Welch's picture
Hi tjdm. This is not going to work out well for you. Restricting the flow between tanks with a turbine will slow down the water exchange between tanks. And if the flow could be slowed down anyway, it would make more sense to restrict the pipe some other way, and save energy by pumping less to the upper tank. The energy saved would actually be more than the energy that could be produced by restricting the flow with turbines.

Also, the amount of energy you could get out of that flow is likely to be so little that it would never pay for the equipment needed to produce and condition it.
Ian Woofenden's picture
Hi tjdm,
It's not only a waste of time, it's a waste of your pumping $, since every bit of electricity you might generate from such a set up will be at the cost of more pumping energy you have to pay for (unless your design has inherent waste built into it, which might be tapped, but it's unlikely that it will be economical). TANSTAAFL. ;-)
Best, Ian
College.student's picture

Hello sir i have a question in myth 2 do you think there is a possibility that it can run a car alternator by the use of ther pressure from the water from the rain gutter ?? Thanks for the answer it really helps me a lot

Michael Welch's picture
Hello student. Please reread the entire myth #2. You will see that it does not make sense to try.
Heetel64's picture

Hello Sir, been a while since I last posted.
The stream behind my land has been cleaned and widened by our local council, giving me a new view of the potential for electricity production.
The flow is still quite slow but now there is 8-12 inches depth of water, with a width of 5 metres.
It is now 2 metres below the level of my plot.
By damming up to a height 1.5 metres, I get my 'drop'.
Across the width (at each metre), I can now install 5 pipes at a height of 1 metre (5 metre drop total). I have connected 2 x 6v bicycle dynamos to each end of 'thrown away' air con spinning section, which equals 12v output from each or 60v total over 5 units. I have also sourced some car batteries from a local garage, for next to nothing.
Can't really comment about flow speed or drop height in relation to power production but this is about producing what I need on a basic level.
My lighting test:- with one charged 12v battery connected to one 5 metre LED strip, I had light for 4 continuous 24hr periods.
So Far so good.
Ultimately, if I want those little luxuries like a fridge, then selling electricity to the grid is my option but from initial calculations, I cannot produce enough electricity to make it cost effective and I have to register and pay for grid connection each month.
I will connect my (home made) ram pump to a sixth pipe just to send water up to the tilapia tank (again freely sourced), which runs off into the hydroponics garden.
Will keep you updated as.
Living off grid, means either investing in making more electricity to feed the needs of those luxury appliances or getting rid of them.

poundingCode's picture

If one had a 'slow moving river' couldn't one use a ram jet?. My understanding is that a 3" ramject could raise water to a height of 100 feet at 0.19/GPS or .73Liter/second). Assuming this was the case, then couldn't one run 8-10 of these in parallel and funnel that into a pelton at the bottom of a 100 foot drop? Eight 3" rams could deliver 5.8 LPS which should be able to deliver 1KWH at 60% efficiency or am I missing something...

Michael Welch's picture
One could, but one should not. Ram pumps also take head to deliver that water, and you probably won't find enough for that in a slow-moving river. But if you've got enough head to run a ram pump, there's enough head to run a hydro generator. So it does not make sense to introduce an additional inefficiency (and cost) into the system just to increase the head. Then instead of using an impact turbine like a Pelton wheel, an impulse turbine works much better in low-head situations. But in a slow-moving river, there likely is too little head available to run either a ram pump or a hyrdo turbine. In those cases, a run-of-the-river turbine must be used. Those rely on the flow of water at their point of use. The problem is that, to my knowledge, there are no viable run-of-river turbines out there. There are some tiny ones, mostly for dragging behind a sailboat.
freedomphysics's picture

Regarding Myth#1, I thank you for emphasizing the combined effect of the law of conservation of energy and the second law of thermodynamics right of the bat to make sure people are not distracted by claims of energy out of nothing. However, I live in a place with plenty of sun and wind and absolutely flat ground. Could you comment on viability of a system that use extra solar/wind power to pump water to a tank on a tower when I don't need it and produce hydro power when I need it. I understand I will lose some energy in the process, but utility of what I save is increased as it is available when I need it. Essentially I am asking, is a residential scale pumped storage for solar/wind energy economically viable?

Michael Welch's picture
Not to my knowledge. Figure out the combined cost of tanks large enough to give you a few kwh, plumbing, pump, and generator, and you will see it gets expensive quickly. The bottom line is that batteries are both more efficient and cheaper at energy storage.
Ben Root's picture
I know that you cannot. Please reread Myth #1 in the article above. A closed loop hydro system is akin to connecting a motor (pump) directly to an alternator (turbine) and expecting something to happen. Sorry.
fredflintstone's picture

What about keeping my well pump on the grid and using the water to charge the battery system? I can put in a catch pond to capture the water. The big question is how much water would it take to keep my batteries charged .

Ben Root's picture
That's the same as just using the grid to charge your batteries...except worse because you have the losses of the well pump motor, moving water/pipe friction, and turbine/alternator. Adding complexity/components to a system makes it less efficient, not more.
fredflintstone's picture

Do you know if you can use the water from your well and then have it go right back to the well head?

bradgallup's picture

I am curious if the scenario would be useful. I understand that pumping water to generate electricity would not provide a lot or any additional electricity. The scenario I would like your opinion on is as follows:
If I pump water and have it fall to two or three pools before it gets pumped back up. The water falling from each pool has a micro hydro generator. The thought (May not be good) is that one generator may be sacrificed to the pumping and the 1 or 2 others generate the power tot he home etc. could this be worth the effort or is it crazy?

Lothorian's picture

Also check out screw turbines. I think this is what your thinking of just revearsed. http://www.epicphysics.com/wp-conte...

Lothorian's picture

Check out Kaplan turbines, they are based off of high flow/low head pressure. Keep thinking the way you are. Dont let anyone tell you, "you can't". With todays technologies anything is possible. Go to convertworld.com, just make sure that you calculate enough flow to achieve the right HP/Torque for startup of the generators. Also there are wind generators that require less HP/Torque that the regular over the counter generators are way higher on. Dig Deep! Never give up!

Michael Welch's picture
Except that there's nothing you can do to change the laws of physics. No matter how hard it is tried, no matter the turbine type, a pump will always use more energy than can be had from a hydro turbine in the same system. The best that can be done is to pump more efficiently.
Ben Root's picture
Sorry, but you answered it yourself, "Crazy". Since the power from a hydro turbine comes from the relationship between head and flow, dividing the head into multiple drops, reduces the height of each drop. But it also adds the inefficiencies of each additional turbine. With multiple turbines, you'd get less power out than one good system using the total height. AND that one system will still always produce LESS than it takes to pump the water back to the top. Making a system more complex never makes it more efficient.
bradgallup's picture

Thanks for the quick reply - I thought it was crazy but had to ask. Too bad would have been a fun project. I guess one addition to the question that I don't think will help but again here comes some crazy. What if I had one pool with a very long drop but had two generators. That would keep the efficiency but double the output. I would capture the energy from the water in two pipes to two separate generators. Does this work or still crazy? Thanks for your time on this even if all it gives you is a chuckle...

Ben Root's picture
You're still trying too hard... Two side by side complete systems, with two full pipes, will indeed generate twice as much energy. but then you'll need to pump twice as much water up hill. One pipe with two turbines side by side (parallel) split at the bottom will have half the flow in each turbine, so each will make half as much power. One pipe with two turbines at the bottom, one after the other (series) the first turbine will use up all the pressure, and the second will have no pressure to work with and thus make no power.
Ben Root's picture
You're still trying too hard... Two side by side complete systems, with two full pipes, will indeed generate twice as much energy. but then you'll need to pump twice as much water up hill. One pipe with two turbines side by side (parallel) split at the bottom will have half the flow in each turbine, so each will make half as much power. One pipe with two turbines at the bottom, one after the other (series) the first turbine will use up all the pressure, and the second will have no pressure to work with and thus make no power.
mosapper's picture

I am just getting started with planning an alternative power generation. What I want to know is if I build a solar array with batteries what do I do with the excess power generated by the PV. So can I use water fed by gravity as a battery? Meaning once my finite lead acid batteries are charged the excess power is dedicated to an electric pump that raises water to an upper storage. Then when I have days of low solar production I can use the microhydro system to recharge my batteries. That being said I understand that if I have multiple days of low solar production and I drain the upper reservoir that I would be forced to switch to a fossil fuel source generator for backup. My biggest concern is letting excess power go to waste because I have reached the capacity of my storage.

Ben Root's picture

The cost/inefficiencies of building a gravity storage hydro system to save a small percentage of extra PV power would be wasteful in and of itself. This is where grid-tied PV systems make so much sense...you can bank your summertime excess energy for wintertime use, as a credit with the power company. Grid-tied PV systems are one of the best things going for individuals and our society in terms of efficient use of renewable energy. If you are off-grid with no hope of bringing in utility power, then good PV system design (PV vs battery capacity) will reduce waste, albeit, it's difficult to design for wintertime loads without having summertime excess. Off-grid systems are more complex, more expensive, higher maintenance, and less efficient. See an article on the choice to go off-grid in the next issue of Home Power (#165).

Ian Woofenden's picture

Hi mosapper,

This is not likely to be an efficient or cost-effective system strategy. You're signing up for _five_ systems -- PV, battery, pumping, hydro, and backup generator -- instead of just PV, battery and generator. The most common strategy is to size your battery bank to cover most of your low-energy times, and use a backup generator sparingly. If you have a second RE source, such as wind or seasonal hydro, you could have a hybrid system. And if you are willing to be careful with your load use, you could possibly avoid having a backup generator, though that's not common.

If you're on-grid, any surplus will be sold back to the utility for short-term credit. Off-grid, the best way to manage surplus energy is to use it! Being aware of your system's fluctuations, and finding ways to use the energy when your batteries are full is a common off-grid strategy. Around here, when there's more sun or wind than our normal daily loads can use, we vacuum, launder, cut firewood with the electric chainsaw, run the planer, charge cordless tool batteries, make sure our laptop batteries are topped off, and revel in using more light. Folks with electric vehicles can use them as a large dump load to absorb surplus (though you have to be willing to live with times of shortage and not use the vehicle as much).


Ian Woofenden
Home Power senior editor

Heetel64's picture

By the way, if you want to go sustainable, then luxury items ( microwave etc ) do not have a place.
Please remember that the amount of energy put into the process of giving you a solar panel or even all the other bits and bobs that you intend to use, has already had a negative impact. For example, using a fossil fuel burning method of transport to collect or have delivered the components that you require is a burden you will have to shoulder. I understand that you no longer want to be part of the ongoing carbon footprint thing, but think long and hard first.
What type of water supply do you have ?

Heetel64's picture

Had to think about that one for a bit. The answer ( I believe ) is to found in the last four words of your post. The reservoir part of the post is your ( so called ) backup or plan B.
I put myself in your position and find my self having to consider the merits of expanding my storage capacity.
I would also have to accept the fact that at some point, The newly expanded storage may be full and then I am left with excess again going to waste.
I would choose the expanding the reservoir capacity if at all possible route.

Ian Woofenden's picture

Hi Heetel,

Remember that setting up a "pumped" storage system has at least three major drawbacks:
• It has a (significant) cost and also embodied energy, plus maintenance
• Every step of the way, it has inefficiencies -- pump, plumbing, hydro turbine -- so you'll end up with much less energy than you started with
• It is limited by your storage capacity, and it actually takes quite a large reservoir to be effective storage (hydro "collectors" are typically measured in square miles of watershed)

You'll generally be much better off investing in a modest back-up generator and using it sparingly. In addition, having "opportunity loads" ready to use your surplus can be a great strategy to make the most out of your RE generation.


Ian Woofenden
Home Power senior editor

anazoran's picture

I like your explanation about shower. It is clear that we can not run water all the time to make some electricity. How about installing microturbines in bigger water pipes like ones in our streets. Someone is always using water so flow is there all the time. They are not small diameter either and the pressure is not bad. Of course the cost of excavating them and either installing turbines or new pipes with turbines would be too much. But installing turbines into pipes for new communities to be buit in the future sounds like a good idea. Would it work? Energy could be used for street light or some other good use for all residents

Ian Woofenden's picture

The only time this sort of scheme will make sense is when there is excess natural pressure. In other words, when the water comes from a reservoir above the city and pressure reduction is needed.

Most municipal water pressure is created by pumps, and pumps use electricity. That means that the "hydro power" potential in them is not free and natural, but has a cost. Any hydro-electrical generation from these lines will be less than the energy used to generate the pressure in the first place. In addition, the goal of a hydro system is to get all the energy out of the moving water, reducing it to no/low pressure. But the goal of a municipal water system is to have adequate pressure for use everywhere in the system.

Practical hydro-electric systems are based on natural flows of water, and in the rare cases where there is a surplus pressure in a naturally pressurized water system, a hydro turbine can provide both pressure reduction and electricity. These situations happen on occasion in the mountain west and elsewhere, but rarely in typical water systems.

Ian Woofenden
Home Power senior editor

OrangBali's picture

Hi all,

I'm working on a project in very rural Indonesia with multiple villages and we're wondering if microhydro is an option. They are all situated on a large river that moves fairly steadily and basically becomes a peat swamp during the wet season. Are there any options for doing microhydro in this type environment to provide power for a village with maybe 100 households? Thanks if there are any suggestions.

twocreeks's picture
twocreeks (not verified)

The previous comment has the same info I have re tech for low head
and as stated you do need some head, When you say bog I think that something is making the water back up creating the bog (still water. This could be some sort of dam, natural or otherwise. Perhaps there is head beyond the "dam" which is a close enough source
to where the power is needed. My understanding is that only 3 feet of head is necessary to use a turgo downdraft turbine as in the link from the previous comment. Good luck.


Ian Woofenden's picture

Hi OrangeBall,

Flat water is a difficult resource to tap. There have been a variety of attempts -- from propeller (large and small) to paddle wheel and beyond -- but the results have been spotty, and no long-term products have emerged in the market.

To effectively tap hydropower, you need head -- vertical drop. With a "low-head" system, the whole watercourse is typically dammed to create some head. This is often difficult physically and/or politically.

One lower-tech, small-scale method is shown at
, but this still requires damming the watercourse to create some head.


Ian Woofenden
Home Power senior editor

hobbes79's picture

Hi guys, hope you are still reading comments on this. Really enjoyed reading your article.

I am currently doing a report for my final project for my university degree. The report is based on adding a crossflow turbine into the sea water side of a ships cooling system (basically the sea water is pumped on board, through a cooler and discharged overboard). The volumetric flow of the sea water circ pump is 2113 m3 per hour. As I don't know what sort of pressure drop occurs across the crossflow turbine I was going to pump it up to a reservoir tank and from there pipe it down to the turbine (thereby avoiding having to try and calculate the drop).

Do you think this is a viable idea or if you have any suggestions I'd love to hear them!

Thanks again for the article.

Ben Root's picture

Hi Hobbes,

As Michael mentioned, there is no wait to "gain" energy from your proposed scenario. You'll be running the pump harder (and thus using more energy) to either spin a turbine, or to gain height/head for later use in a turbine. Running the cooling circulation pump harder will always use more energy than the hydro turbine could gain back...a net loss. If the pump is already creating any excess pressure (e.g. shooting water out the side of the ship), harnessing the excess is tempting, but you'd be better off turning the pump down to save energy, rather than trying to recapture that energy with a second inefficient component (and that's assuming that the ship owner is OK with the waste-water dribbling down the side of the hull). Reread the article, and try to image any proposed system in it's simplest element...running a pump to power a turbine will never be a net gain...there is no free lunch.

Michael Welch's picture

Hi there. Thanks for checking out the article. But please read it carefully. You are describing a system similar to one or more that the article is about.

The bottom line is that if you restrict the flow with a hydro system, pumping power will need to be increased to make up for it. That's a net energy loss, there's nothing to be gained by doing this.

But if you have EXCESS flow in the system, then you can reduce the pumping power to be only what is needed. Then you have energy savings, which is even more valuable than generating energy.

hobbes79's picture

Hi Michael & Ben, a belated thanks for the replies!

After reading through he article I totally understand why the system described would never work - rookie mistake. I was just thinking about this again and was wondering if you could tell me if the following could possibly work?

A lot of larger ships (ie container ships and bulk carriers) can be set up to fill their ballast tanks with sea water by using the head of sea water alone (pumps can also be used but quite often are not to save energy) as the sea chests are located several meters below the water line. If a cross flow turbine were to be installed low down on the ship, but above the top level of the lower ballast tanks in the ballast water intake would it viable? I was just wondering what would happen to the water pressure once it went through the turbine, if it would drop (and need to be pumped which is a non starter or if it could be gravity fed to the tanks)?

Thanks again and I love the site - really interesting stuff!


Michael Welch's picture
No doubt it would be able to generate some energy. But the question is whether it is enough energy to warrant the expense and effort. Since the water would be flowing for relatively short periods of time, I suspect it would not be worthwhile.
cyrus's picture

i know you said a Closed-Loop / Pumped Storage isnt possible but can you comment on this article i found :


Ben Root's picture

Hi Cyrus,
A very interesting and optimistic article indeed. The key point here, in relation to my article, is the word "storage" in the "Pumped Storage" concept. Pumped storage is NOT an energy source, but an energy storage mechanism. The article referenced is specifically discussing a process to store excess wind and solar generated electricity when it is readily available, but not needed by the utility grid customers. Storage of these green, yet intermittent energy sources is often criticized (rightly so) as a weak link in an otherwise pretty ideal energy solution. And as mentioned, the utilities have been using pumped storage for years already with coal (and other, including large hydro) power plants that don't react quickly to changes in power demand.
It is interesting to read that pumped storage is up to 80% efficient at these large scales. This is higher than I would have guessed, and rivals current battery technology. The important distinction may be that it is difficult and expensive to create battery banks large enough to store energy at utility-scale quantities. However, it may be also relatively difficult and expensive to build home-scale pumped storage hydro systems small enough to operate at an efficiency equal to a simple battery bank. Why build such a complicated system when you can just install a battery in your utility room?
Regardless, the key point here is that these systems are storing energy (at a net loss) that is being supplied from other sources (solar, wind, coal, or even an actual hydro resource). The pumping element loses energy to inefficiencies; the hydro generating element loses energy to inefficiencies. Each loop through the system looses more energy. Perhaps in some cases, those losses are worth having a system to store available energy until it's needed. But in no case, is that pumping helping to gain energy.
Make sense?

Heetel64's picture

Hi twocreeks, Ian and myself have more or less answered your query albeit in different ways. I have pondered your dilemma and would like to suggest something. As you have access to a mechanical engineer, enquire if it would be feasible to ' up ' the .85kw using a higher gear ratio somewhere within the system design.
When stuck on ' how to ', I always revert back to the basic premiss of the humble bicycle dynamo. The speed of the spin is directly related to the bulbs brightness.
Also you might want to re-look at the mechanics within your system to see where you can improve on the so called ' friction slow down factors ' that can affect output.

Heetel64's picture

Hi twocreeks, just to use electricity as it is generated is not feasible unless you have one hell of a power generating water source. I my self considered the pump to storage tank method using some sort of 'ram' pump. Not going to work as you have to continuously put more water in than you take out. In a nut shell, my conclusion was to have between 6-8 deep cell batteries connected to shunt charge regulators. Bearing in mind that they would be receiving a 24hr charge from the energy source, I then had to consider how to harness the excess current being dumped by the shunt charge controller after the battery banks were fully charged. Simple solution was to have the excess dumped via a wire connected to a copper or brass coil immersed in a tank. This would boil the water and create steam giving me another source of energy from what in effect would be wasted energy.
Steam powered turbines, could be an option for you to consider.

Ian Woofenden's picture

Hydro systems without batteries or the utility grid are possible, but typically require a 2+ kW resource, and then you must live within that maximum power cap. These use a "load control governor" to keep the turbine fully loaded all the time — either with the user loads or with diversion (or "dump") loads, which are typically air or water heaters. Diversion loads must be 100% reliable and able to take the full output of the turbine.

Connecting to the utility grid is perhaps the best option, since ALL hydro output can be either used or sold to the utility for credit against future use. Grid-tied systems can be designed with batteries (to provide utility outage protection) or without.

As Michael Welch and I have pointed out, pumping to gain head and power is a no-win situation, since it takes energy (or surplus water in the case of a ram pump) to pump, and there's no free lunch.

Ian Woofenden, Home Power senior editor

twocreeks's picture
twocreeks (not verified)

Hi Ben,

I, in fact, have a 10 ft. water fall 100 ft from my home.
According to the calculations I have done with assistance of a mechanical engineer it has been determined I could get about .85kw
theoretical from that fall.
At top of bank I have 28 ft of head which could produce 1.9 kw. So my dilemna is getting water up to the bank in an efficient manner. Ideally, I could put an intake into the creek and gravity feed it to a tank (in-ground) to feed a turbine below.
However, as you pointed out unless that works using an electric water pump (which is already in place from previous irrigation use) to do the tank filling is a losing proposition. Would it be possible to use a Fyfe ram to fill the tank? Would it pump fast enough to feed the turbine's needs? I have always thought a cross flow turbine would be best, however I am open to suggestions. The flow rate is 300 gpm in a 4" pipe which would be reduced down to about 1.7" depending on turbine. Any thoughts?

Michael Welch's picture

Hi there. Ram pumps also require a downhill flow of water. As long as you have enough flowing downhill to run a ram pump, you might as well just use that downhill flow with a hydroelectric system instead of introducing the inefficiency of pumping uphill first.

twocreeks's picture
twocreeks (not verified)

Thanks Michael,
The elevation (head) gained by going further upstream is negligible compared to the head I attain by going to top of bank.
so I'm looking for a non-electrical mechanical advantaqe to get to top of bank. So is there a Fife Ram large enough to keep a large tank full to satisfy the turbine requirements? It may not work or be known. I think getting a GPS reading for elevation from intake locations may be interesting. If I could run a pipe up the creek to feed the tank it may work?

Michael Welch's picture

OK, let me try to be clear about this.

Stop trying to think of ways to move water uphill so that you can then recapture that same water flowing downhill to make electricity.

Just stop considering it, it will never pay off.

Use whatever natural downhill flow you have, but don't try to move it back uphill. If you have little or no natural downhill flow, stick with solar.

Ian Woofenden's picture

Though pumping with a ram pump has no ongoing cost, it's still unlikely that such a strategy will be a net gain, when you consider the system cost and the waste water. I suggest that you map your full watercourse and segment it with head and flow measurements in various places. See my hydro design considerations article, and particularly the example mapping at http://www.homepower.com/articles/m...

Once you have the clear and accurate data showing head and flow across your whole property, you can make calculations of potential power and energy, and then make an intelligent decision about your real resource. It is the _natural_ head and flow that is your resource, and most any attempt to manipulate them ends up using energy, not gaining.

Typically, discussion of a "large tank" is a tip-off that you may not have a sufficient hydro resource, since your actual energy resource is what is continuously flowing down your hill, and you simply need to get that flow into a pipe and tap the pressure of your available head.

Ian Woofenden, Home Power senior editor

oluwalami's picture

if i have a 2000ltrs Storage tank 3meters above ground, would it be able to run a pelton wheel microhydrogenerator at ground level thhrough a 25mm guage pipe (if the water is running under gravity)

asmuktar's picture

I am trying to find out if i can use a borehole on a turbine at home to generate electricity. i am stuck with calculations of flow rate and tank capacity. Is there anyone who has done this or something similar? i want to design it in such a way that the water will be recycling. i looked for surface water pumps i can to pump the water back to the overhead tank. but that seem too difficulty. Help please!!!

lemonwood45066's picture

I will be purchasing property either to build or with an existing home in the near future and would like to utilize a microhydro power system. Can you recommend a consultant that can determine if a stream is practicle or not. I live in southwestern Ohio.

Thank you

Michael Welch's picture

Here is an additional resource. This Yahoo Group list server can be very helpful, but they will insist that you have good info on head, flow, and what your needs are. But they should also be willing to take the question of "who can help me in my area."

Ben Root's picture

A quick Google search came up with some "maybes" for hydro installer in Ohio. http://leffelcompany.com builds "Small" hydro, which is a lot bigger than mciro hydro, but you could call them and ask for better leads.
In the mean time check out our archives for several great micro hydro articles, especially http://www.homepower.com/articles/m... , If you and a friend can walk the potential creek, you can do a site survey yourself. Then calling any of the micro hydro suppliers or installer with your head and flow data will give them what they need to rough-estimate systems, performance, and costs for you.

erkme73's picture

Hello Benjamin. Hopefully you're still responding to comments on this page. I registered specifically to post this comment/question...

I'm considering purchasing a rather large parcel that has a cave system, and a well head that puts out over 3 million gallons of water per day. The well is at ground level (as best we can tell). While we can't see the actual opening, the width of the "river" created by the well on the rock face is no more than about 20' wide.

Is it realistic to assume this well could somehow be "tapped" with a micro hydro generator?

Ben Root's picture

I'm having trouble visualizing the scenario, but basically the thing to remember is that you need flow (3 million gallons a day is a lot!), and head (vertical drop) to make power. If the well or spring is coming out at ground level (as you say), there would have to be lower ground somewhere else to create the head you require. With that much flow though, you may be able to get away with as little as a meter or two of head.

erkme73's picture

Thanks for the reply, Ben. I guess my question is, is it feasible to use the pressure coming out of the spring head to drive the turbine (vs. generating "head pressure" from a drop)? Since all of the flow is coming out of a defined opening, would diverting some or all of this flow provide the needed pressure to make up for a lack of vertical delta?

I intend on visiting the property again within the next few weeks (it's a 10+ hour drive). At that point, I can take detailed photos and make measurements if that would help.

Ben Root's picture

If there is pressure there, it may be usable. How are you measuring it? Is the spring exiting a pipe that you can cap with a pressure gauge? Realize, that once the spring exits into the free air, all pressure is lost? It may be time to contact a hydro professional from out contractor directory or advertisers.

erkme73's picture

You've given me the answer - which is that there may be usable pressure if I can contain the flow before it exits into the stream. Currently there are a number of large rocks in front of the exit point, so there is no practical way to measure the pressure. But on my trip to the site, I will see how feasible it is to get to a single exit point.

I agree, it may very well be time to have a professional do a complete survey of my options. Thanks!

Heetel64's picture

Hi erkme73. A couple of bits for you to ponder whilst you're up at the property. If you have any bends on the river then water naturally flows faster on the outside and maybe you could consider putting in a vertical turbine. A vertical sluice gate would be a way to divert water depending on depth of water.
Q. Are you intending to power directly from flow, charge batteries for later use and / or sell back to the grid.
A word of caution finally, take a good hard look and visualize the difficulties involved in achieving your project and don't forget to study up on how things got done by our ancestors all over the world.

Heetel64's picture

Thanks for the reply Ben and ladymysterious. I guess that I am lucky enough to be in a unique position as there is a small stream feeding down from a mountain somewhere and a another canal carrying water from a naturally ocurring underground spring now found in the grounds of a casino complex which join together just at the beginning of my land.
I intend to construct an arch shaped house based on the water source which is the stream and also the climatic tendencies of the area which is rainy up to 30% on a daily basis.
Most of the blogs that I read seem to be about maximising natural resources but my view is simply to take what's on offer and construct accordingly. Plan B and plan C consist of a self made ram pump to elevate the inadequate fall of the water source and a solar powered system to pump the water out of a soon to be dug well which will be sent to a holding tank to create an artificial fall of water. The area is an ancient swamp that is now a large town of people who have do not know what is beneath them.
I have already stripped an old air conditioning unit to get at the fan which is 2 feet in length. It is made to rotate freely in a moisture laden environment. The motor will be redundant as it will simply have 2 bicycle dynamos attached at one end to give a max of 12v. Yes I know that this depends on flow but even low flow creates enough current during the night to charge batteries, remember that water flows 24hrs.
6 batteries with their relevant charge controllers will give me electricity, hot water and possibly an excess of current to sell back to the grid IF I GET IT RIGHT.
With the greatest of respect to you Ben, the links and references that you speak about will probably not help but are sure to enlighten me.
As for you ladymysterious
your positive encouragement is beyond value and I cannot thank you enough.

Ben Root's picture

Hi again. Your creativity is inspiring. And of course, so is the possibility of having a viable hydro resource.
I must admit that I'm more of a theory kind of person than a tinkerer...That can be a drawback. But here are a couple of things to think about, since they directly relate to the article above.
First, the idea of using a ram pump to create head: remember that ram pumps only raise a small percentage of the water moving through them. They are trading flow for head, but not very efficiently. You might want to ask yourself if there is actually more energy available if you use all your currently available flow at your existing head, rather than just a fraction of it at higher head.
Second, the idea of using solar powered (PV) pump to raise well water: For sure you will generate more energy directly from the PV modules directly than you would ever gain by pumping water with them to then run through a hydro turbine. Remember adding energy conversion components to any process, by the basic laws of physics, reduces overall system efficiency.
I really suggest reading one of our article on hydro site assessment. Whatever you choose to do, good luck on your project .

Heetel64's picture

Stream with low to very low head behind my land. Length of stream roughly 20 mtrs with overal drop of 2 mtrs. Would one option be to create a step at the beginning and level off the rest of the stream bed?

Ben Root's picture

Hi, with the right amount of flow, usually "a lot", two meters can be enough head. The energy output will depend on that flow. Check out some of our other hydro articles for resources on low head hydro. There's a great article on small systems here: http://www.homepower.com/articles/l... and the author is in the US these days and can be contacted directly for more info. Energy Systems & Design at www.microhydropower.com/ out of NB Canada, and http://waterturbine.com/ out of MA both manufacturer low head turbines. All of these guys are long-time reputable manufactures in the industry. Any of them would be able to help you determining the viability of your resource, and the best approach. But I do suggest reading the many other HP hydro articles to learn the jargon, variables, and right questions to ask.

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