What is Microhydro Power?

Jerry Ostermeier of Alternative Power & Machine
If you have the right site, a microhydro-electric system can be a terrific RE investment, generating energy 24/7.
A microhydro power resource.
Home-scale microhydro-electric systems can give the best renewable bang for the buck. With the right situation and implementation, you can have a low-impact, low-maintenance, reliable system that supplies clean energy over the long haul.
Measuring flow in a small stream.
The “bucket method” can be used to measure flow in small streams. Larger streams require an alternative measurement method.
Measuring static head in psi.
95 psi shows the static head of almost 220 feet of head.
A self-cleaning microhydro intake.
For most microhydro systems, a simple and inexpensive, self-cleaning intake right in the stream flow can do the trick.
Jerry Ostermeier of Alternative Power & Machine
A microhydro power resource.
Measuring flow in a small stream.
Measuring static head in psi.
A self-cleaning microhydro intake.

What is Microhydro Power?

Hydro-electricity is fundamentally the combination of water flow and vertical drop (commonly called “head”). Vertical drop creates pressure, and the continuous flow of water in a hydro system gives us an ongoing source of pressurized liquid energy. Pressurized, flowing water is a very dense resource, and hydro-electric systems convert a very large percentage of the available energy into electricity because the resource is captive in a pipe or flume.

People have been tapping the energy in flowing water for centuries, first for mechanical power, and, in the last hundred years, for electricity. Early applications included milling, pumping, and driving machinery. Unlike wind and sun, the right hydro resource can be available 24 hours a day, 365 days a year. This allowed pioneers to run irrigation pumps and grain mills, and allows people today to make clean, renewable electricity at a reasonable cost.

A simple formula can give you a rough idea of how much capacity your stream might have. Take the head in feet, multiply it by the flow in gallons per minute (gpm), and divide by a factor of about 12. This will give you the potential wattage of a reasonably efficient, small system. For example, if you have 30 gpm available and 40 feet of head, you will be able to generate something in the range of 100 watts [(30 × 40) ÷ 12 = 100). Over the course of an entire day, the generation would be 2,400 watt-hours or 2.4 kWh (24 hours/day x 100 W).

Within this formula is the understanding that systems with low vertical drop (head) need more flow to generate the same amount of energy. Typically, low-head systems will have high flow, and high-head systems will have lower flow. Adapting the example above, if we have 400 hundred feet of head, we only need 3 gpm to generate the same 100 W.

There are a wide range of small hydro turbine types to suit the head and flow of the site. Large wooden overshot and undershot wheels tend to be less efficient for generating electricity, though they may be appropriate for mechanical work. For electricity generation, systems can be divided into “low head” and “high head.”

Low-head systems may have less than 5 feet of vertical drop—sometimes they may have only 10 or 20 inches. In this case, most or all of the water in a small stream will run through the turbine to maximize output. The runner (the part of the turbine that receives the water and turns its energy into rotation in a shaft) for low-head turbines may be a Turgo or Francis type. These systems typically have short pipelines or sluiceways that then allow the water to drop through the runner.

High-head systems may be defined as any site with more than 10 feet of head. Common runners are Turgos on the low end, and the most common, Pelton, for medium to high heads. These systems may have hundreds of feet of pipeline to develop the head (pressure), with the water delivered to the runner via multiple nozzles.

The basic components of a small hydro-electric system, running from “water to wire” are:

  • Diversion and intake screen—Directs water from the stream or river into the pipe or channel
  • Penstock (pipeline)—Carries the water to the turbine
  • Turbine—Generates electricity (includes nozzles, runner, and generator)
  • Electronics and batteries (if used)—Regulates turbine and stores energy
  • Dump load—Absorbs surplus energy
  • Transmission and distribution—Delivers the energy to its end use


Comments (31)

CON's picture

I see the same stuff over and over, people are confused about the first law of thermodynamics......it's very simple, energy in same as energy out; but if you lucky, the energy is always waiting...... my problem is to store such easy energy.
First, I may get my hands on a serious lead-acid battery bank, but I havta admit, I will need both acid and distilled water to maintain same.

If I use the battery bank (via inverters etc) to store and repower to the grid, what are the profits vs the full cycle life of heavy duty batteries?
My best guess is, not good, but it would be great to have power in a snowstorm and help my neighbours too.
The question stands, how much to convert 24v DC to mains including all the required technical standard equipment and provisions? CON

Ian Woofenden's picture
Hi Con, This equipment could easily cost $3-5K+, depending on the size and complexity of the system. A single, whole-house inverter could be half of that amount, and the cost of the battery bank will vary depending on the battery type and size. My modest battery bank is in the $2K range, and my inverter approached that in cost, when you include the associated equipment. It's worth remembering that it's a _system_ -- and you need all the components, intelligently matched. Pricing just the generation gear (hydro, solar, wind) doesn't give you the full cost picture. Regards, Ian Woofenden, Home Power senior editor
CON's picture

Michael, I have never seen a more patient man! I have to admit, I didn't read ALL of the subject matter or ALL of your replies, but I've def seen enough...
My question is much more prosaic..... given a fall over 100 metres of a natural stream and bearing in mind the wish to preserve a vibrant habitat, how might I best 'syphon' off enough energy to make it pay for itself.
What are the real world costs of 'say' a 2kw generator, and all the other circuits/controls necessary to connect to the grid?
What is a typical, real world, payback? Who might you recommend as suppliers?
regards, Con

Frank Heller's picture

With 8 gpm at 40 ft. head and a 200ft penstock w/1 1/4" d. you'll only get 19 watts with a Pelton wheel.

With 16 gpm at 80 ft. you'll get 98 W.

These are estimates, but this is continuous charging of a battery.

Site would have to be assessed for other options like an impound and periodic power generation, or a riverine device to use flow. I've seen 12 ' water wheels with very small buckets. have to calculate torque but with a gear box you'll get something.

W.W.'s picture

I have a off grid site with 40-80 feet of head (40ft on my land) over around 800ft but only 8-16 gpm flow most parts of the year. I'm trying to charge a battery bank to run LED lights and possibly charge 20v batteries, and trying to figure out if hydro might be a viable option. Thanks in advance for any input

Mitch's picture

Hi all. I’m after some advice, please... ( but I’m rather a rambler, so please forgive me)
I have some farmland (an Olive and Almond farm) in northern Spain. No water and off-grid. The farm is on a hillside (so no problems with ‘head’ height). I’m also keen not to use heavy metal storage systems for my power storage. So I’m looking at a combination of solar, wind and hydro. ——— My hope is to incorporate a closed loop microbore hydro-electric system to pump water uphill all day to a holding tank and then allow a downhill flow at night for dark hours power generation/consumption. The Solar power would be the primary pumping/ daytime consumption provision; Augmented with power from a wind turbine.——- I simply have no if my idea can be supported by the availability of current products in the market place. I also lack the experience to know if the plan is even achievable given most everyone’s meagre resources. I would like for my wife and I to finish our days making as little impact on the environment as possible and create a haven for our grandchildren to see what is possible as an alternative.... hope this is no too idealistic :-)

Claire Anderson's picture
Hi Mitch ~ It would be helpful to know what electrical loads you wish to power, as well as an assessment of the renewable energy resources (daily sun-hours and wind speeds at tower height) at your site. Insofar as "direct" solar power, solar thermal systems with a PV-powered circulator pump could be a possible option; as could a solar oven for cooking; and passive solar gain (with a well-insulated, small home with appropriately located windows and some thermal mass in the floors) for free space heating. You didn't mention how your domestic water is provided, but direct PV water pumping to a storage cistern is also an option, with potential gravity-feed to your home. Home Power has a terrific library of past articles on all of these subjects, BTW. Best wishes, Claire
Mitch's picture

Hi Claire, as I have mentioned to Michael, I am most grateful for the time you guys have taken to discuss this with me.
A brief synopsis of the problem looks like this: Small mountainous farm in the Tivissa province of the Tarragona region of Catalonia. No water on site but pumped irrigation water is nearby. There is a spring in the local village which suggests an aquifer, given the mountainous location. A micro-bore water well may be possible but the normal practice is to ship water to the site by Bowser and store in tanks. This is not potable. The link (https://www.worldweatheronline.com/...) is what I have been using to determine averages for windspeed in the area along with hours of sunshine.
There is an existing Barn and I am limited to rebuilding that to a traditional stone "look". The electrical loads would look something like - Refrigerator (gas models are available) Washing machine, TV, Internet routers, Lighting, water heating.
I have in mind a simple black painted, copper pipe lattice in the 'roof' of a gazebo/patio shade to augment a daily end-of-day hot water supply. I intend to use a solid fuel hot water system for the winter season to augment any PV system.
My end target is to have as small a consumption/environmental impact as possible in the circumstances. I read a book by Rory Spowers "A year in Green Tea and Tuk-tuks" that inspired me, as a teacher, to create a working example of something to show others (my grandchildren mainly) in the vein of a bio-versity (from the book). I visited 'Samakanda' to see their progress and was disappointed. Hope this explains my retirement plans ;-)

Michael Welch's picture
This idea will not work for you. Pumped storage does not make a very good battery. First off, converting your solar power to pumped storage then back to energy to use will have an efficiency of less than 50%, whereas batteries are much more efficient at the conversion.

But there are other problems. Say you had 100 ft. of head available, and you needed 500 W of power. That would require about 50 gpm. If you needed that amount of power for, say, 16 hours a day; that would mean that you would have about a 50,000 gallon tank that needs to be filled during daylight hours each day. For the math around this, check out https://www.homepower.com/articles/microhydro-power/design-installation/...

And what if you suddenly needed 1,000 W for something, where would that extra 500 W come from? Battery/inverter available power is instantaneous, but ramping up and down a hydro plant to meet changing loads is practically impossible.
Mitch's picture

Hi Michael, and thanks for the rapid response.
I can see the wisdom of your words and see why my idea is not the most efficient.
The thing for me is to try and avoid the use of batteries. I have the space to build a large holding tank at both the header height (of over 100ft, if required) and the capacity, to ensure 500-750W. In all honesty I would probably only need 5-6 hrs of power (we're not night owls). I'm also looking a bio fuels and to convert and older diesel generator to supplement my power requirements.

So given that I'm trying to avoid the use of batteries and accept the loss in efficiency... is there a system or are there components out there that could help me achieve my goal?

Michael Welch's picture
Not that I know of. But I think your basic premise is flawed. Sure, batteries have toxic materials. But they are 100% recyclable and can last a long time. Combine that with the wastefulness and expense involved in everything you need to try to avoid them, and it doesn't make sense to me, even from a strictly environmental standpoint.
Mitch's picture

Hi Michael.
If the batteries can be 100% recycled and there is a facility for that, I can see the practical and environmental argument for using batteries. Your arguments and strong and quite convincing in these circumstances. I really am very grateful for the time you've taken to discuss this with me. I will now start investigating types and quantities of recyclable batteries as a more efficient alternative to the Micro-hydro closed loop system.

IamRuffwood's picture

Hi. I am designing a 30kW self contained micro hydro system. My question is can I decrease the need for head by controlling the flow rate through the hydro? I will have about 6ft of head on 20 ft of pipe. I have about 100 gpm pushing through a 1-1/2" pipe out of a 3/4" nozzle.

Frank Heller's picture

Power in watts(AC) = net head (ft) x flow (USGM/9
you have 6'x100gpm/9 = 66.66 watts.

Powerspout's pelton calculator using 68.7 gpm and 35' head, one PowerSpout will produce 142 Watts.

You still want a 30,000 Watt system?

Ian Woofenden's picture
Head and flow are equal factors in the hydropower equation. Decreasing head or decreasing flow will decrease output.
If you only have 6 feet of head and 100 gpm of flow, you won't want to decrease anything. That's only about 50 watts in rough capacity.
Flow rate is determined by the number of nozzles and their size (in systems that use nozzles).
See our many other hydro articles for details on system components and design.
Ian Woofenden, Home Power senior editor
Powerman's picture

Hi Michael

Great website.

We are building a new house in Auckland and it is my vision to go off the grid in the next year. I am looking at 10kW of solar panels and through installing multiple check meters throughout my distribution system to establish a good load profile for the house. Initially we will remain grid tied and export our surplus energy generated. Once I know what my load profile is we will install a control system to manage loads during the day and also size battery banks for night storage so as to optimise on my return on investment(ROI). The idea will be to use as much power as possible during the day in a controlled/ staged manner.
I am however considering using some of the surplus energy at day to pump water into a storage tank up a nearby hill as potential storage and then release this energy at night back into a bottom tank. We propose for this to be a closed system. I realise that the system is not very efficient from past commentaries and posts, however as the surplus energy that will be used for the pump is Free (from solar system) surely this could be a way of "shifting" renewable energy in time from day to night? The intention would be to then use this energy to either charge batteries or small back up power or to say feed small loads like lighting etc. at night time.
Do you have any comments to the above in concept?
Many thanks

Mitch's picture

After a recent visit to Hamilton, my desire to live off grid with minimal environmental impact was given an enthusiastic boost after meeting so many eco-Kiwis. Really hope you’ve made some progress, mate. I’d love to hear from you and would gratefully accept any advice you can offer as your ideas are closely aligned to my own.
Many thanks

Michael Welch's picture
Hi Leslie. Yes, my comment is that it is probably not a good idea. Using deep cycle batteries is much more efficient than pumped storage, and cheaper per KWH too. http://www.homepower.com/146.76
Powerman's picture

Thank you Michael. Much appreciated.



poster's picture

Thanks for the artical, very good. I have pump that pumps 1000 GPM through a 8 inch line, and runs most of the day. It has about a 2 foot drop from the outlet of the pump, to the ground. Can i install a generator in this line to recoup some of the cost of running the pump?

Ben Root's picture
If you just want to recoup the energy available in the 1000gpm with the 2 ft drop, to lesson the load on your pump, you can do that easily. Just lower the outlet of the pipe by 2 feet. The "suction" from those two feet will reduce the load on the pump without all the costs (efficiency and monetary) of putting in a little 2 ft hydro system. Just be sure that the water still has an easy discharge to free air; that is, don't make the pump have to work to push that velocity of water against the ground or a pool of unmoving water. Use smooth sweeps instead of 90° els turn down (to lesson the friction losses of turning sharp corners)...you're trying to reduce the load on the pump, not add to it. This idea/solution is basically the equivalent of reducing the height that the pump is lifting by 2 feet.
Michael Welch's picture
Hi there. You can, but it doesn't make sense to do so. You'll just make your pump work harder to make up for the generator. The best you can do is to save energy by not pumping as much, assuming you don't need that full 1,000 gpm. Here's an important article for you to read.

Thomas Sullivan_2's picture

Looking for info on a hydro coil , How do you keep fish from going through the hydro coil. Tom Sullivan Thanks

Dean Scott's picture


I live in Washington state and have done all the work re feasibility, etc. and would like to finally DO IT. I have been told my place is incredible!!

How do I find a manufacturer/installer in my area? I am in Lewis County, WA.


Ian Woofenden's picture
Hi Dean, Finding a manufacturer and finding an installer are usually two different jobs. Check out HP advertisers for manufacturers of small hydro turbines. Who you choose will depend on the size of your resource and energy need, the specifics of head and flow at your site, as well as other factors such as price, availability, and your preferences. Finding an experienced hydro installer is much harder, since there are so few people and companies who do this work. I'd start by finding renewable energy (primarily solar) installers in your region and asking who has done hydro before. If you don't find someone locally, you can either bring someone in from outside the area, or you can educate yourself and get involved in the installation directly, perhaps in collaboration with a solar electrician. See our many hydro articles for more information on the specifics of system specification, design and installation. Ian Woofenden, Home Power senior editor
sandyp22's picture

Hydro electric isn't green anyway. It's just a storage medium for off- peak power. Water is pumped 'off-peak' using electricity from fossil/nuclear fueled power stations.

Ian Woofenden's picture

Hi sandyp22,

Definitions of "green" vary widely. My view is that everything we do has an impact, and my goal is to reduce that impact. While large-scale hydro can have a heavy impact, it has less impact than fossil fuels and nuclear.

Hydro is much more than just storage for off-peak power. Though it is used in pumped storage schemes, most hydropower is used directly, and is renewable energy made from the natural combination of vertical drop (gravity) and flow. Many utilities use it as a primary source of energy. In my area (Washington state), it can be 20-40% of the total generation capacity.

Ian Woofenden, Home Power senior editor

SolarManJD@DCemail.com's picture

Ian I agree and I am working on a new Worlds First (stand alone) Solar Powered Hydro Electric Generator

Mitch's picture

Hi, SolarMan. I agree with Ian Aldo. I’m also fascinated to hear what you have planed, have achieved and possibly more importantly, what didn’t work for you. :-)

Heetel64's picture

Excellent point about what is green.
As for the comment sandyp22 made, I can agree with the point raised as well. I live on an island with many mountains and countless rivers and streams, yet we have ( like so many ) shortages. The root of the mismanagement of natural resources is to be found at the doorstep of successive governmental bodies. Yet are they really to be blamed as it generally takes half to three quarters of a term to develop a plan, leaving them almost no time at all to get it off the ground unless they are popular enough to stay in for a second term.
I for one say micro hydro is the way to go.

mgracen's picture

This is an excellent article for the newbie. We are going to Tweet it and add a link from our resources page. Thanks!

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