ASK THE EXPERTS: Microhydro Cost

A stream used for microhydro production
With adequate head and flow, an on-site creek or stream can be an excellent source of renewable energy for your home.
Microhydro turbine
Choose an appropriate turbine to match your microhydro resource.
A stream used for microhydro production
Microhydro turbine

How much does a 4 kW microhydro power plant cost, complete with all of the components?

John Sabor • Memphis, Tennessee

There are so many variables behind your simple question that a simple answer would not be helpful. We need to look at the site and what it has to offer. Equally important is the load you will be running and how best to meet your needs.

My first question is: What does “4 kW” mean? If it means producing 4 kW all the time, this would be a fairly large amount of energy produced for a residential application (96 kWh per day), unless you are planning to heat with electricity. If 4 kW is only the peak load, then you might not need a 4 kW turbine; it could be more sensible to choose a smaller turbine that produces the daily energy that you need. You would meet the peak power demand from batteries (via an inverter), or from the grid.

If this is an off-grid situation, adding a battery and an inverter will maximize the usefulness of the energy from your hydro turbine. Producing 4 kW all the time calls for a very good hydro resource—and a big investment. If you cannot store energy, then much of the energy from your 4 kW turbine will arrive when you do not need it. The control system will have to discard this excess as heat, which may have no value in summer. It is unusual to find a site where significant amounts of water can be stored in a dam, so battery/inverter systems (like the ones used for off-grid solar and wind) are a popular option.

Similarly, an on-grid turbine that is sized to meet your peak demand will export a lot of energy. Will this pay off? If you have a very good hydro resource, then you may not care about wasting energy because it is cheap, but most of us don’t have that kind of resource.  In most cases, you should size your hydro in line with your daily kWh needs, rather than thinking peak power. A smaller turbine that uses less water will also tend to have a better capacity factor or, in other words, it will run for more hours per year.

A small stream that runs steadily and falls steeply can be a very good electricity source. The potential power in watts would be roughly the flow in gallons per minute times the vertical fall in feet, divided by 10. To get 4 kW, you might, for example, use 400 gallons per minute falling 100 feet in height. The water will need to pass through a pipe between the source and the turbine 100 feet below, and the friction of the pipe walls and any angles in the pipe will use up some of the pressure, diminishing the energy available at the bottom. On a steep slope, you might use 500 feet of 5-inch pipe. But if the slope is gentler, you might need 2,500 feet of 8-inch pipe. By the time it is laid, the pipe often costs much more than the turbine itself.

There are many options to consider. Will the turbine adjust its flow automatically to make the best of the water in the stream? Will it be better to buy several off-the-shelf turbines or one big custom-built unit that might not work so well at times of low flow? Should the generator produce AC directly? Should you connect this system directly to the grid, or even with the output of an inverter? Or should it produce DC that charges batteries or feeds a grid-tied inverter like a PV array? Should you invest in a foolproof intake system or will you be happy to hike up there from time to time and clear blockages? Hydro system costs can vary widely depending on the energy needed, the head, the flow, and the distances between intake, turbine, and wherever the energy is being used. It’s easy to look at the cost of the turbine—home- to ranch-scale models range from perhaps $1,500 to $10,000. But that is only a fraction of the cost of the whole system, which includes intake, pipeline, turbine, tailrace, controls, perhaps batteries, inverter, etc.

A fully installed hydro system for the average use of a modern household might cost $20,000 to $100,000 (or more). But it’s not wise to look at these numbers as anything more than a very general range of possible costs. The cost for your system will depend on the resource available (head and flow), the demand (watts and kWh), the distances involved, and the specific components you choose.

Hydro can often be the most economical renewable electricity resource over the long haul. Investing well up-front will make your system last a long time, which decreases the cost per kWh. Let’s hope you have a good hydro site, because it’s a wonderful thing to develop. I hope that helps you start the planning process.

Hugh Piggott • Scoraig, Scotland

Comments (7)

Mike Hann's picture

I had a concept of using a ram pump (uses water as power source) and pump stream water to a higher storage tank and then run a small hydro from this. I have a stream through the property with plenty of water. I could likely get about 50-60' of head. Issue here becomes volume of water I need to run a small hydro. Likely will have a battery pack and thinking of hydro versus solar. Another option would be some type of low head hydro - I only have about 8 - 10' of elevation difference from where the stream enters the property.

Michael Welch's picture
While you may gain head by pumping, you will lose part of the flow because ram pumps can only pump a small percentage of the water that goes through them. Most of the water is "wasted" in getting enough power to push the water uphill. So it really doesn't make sense to ram-pump up hill just to get more head. Your thought of using low-head hydro seems to be your best bet.
chanhl1963's picture

Any test cases used for urban high rise buildings? The water sources can be from domestic water intake or ACMV chill water pipes.

lalitanand's picture

In an industry I have seen filtration system for which water is being pumped into a tank with a flow of around 2.5KL per min and with a head of 2 feet. Now I want to to know will any kind of hydroelectric system can be put in place. If yes, what system and what will be the cost and will that be feasible?

Michael Welch's picture
You cannot get any more energy out of a system than is put into it. In fact you get less because there are efficiency losses with every step. This means that you would have to pump harder in order to make up for the hydroelectric energy you take out of the system. And that would result in a net loss of energy. So your best bet is to figure out how to pump more efficiently, with less energy, not to take energy out of the system that you just put into it.
Sanjay Gangakhedkar's picture

In most of Industrial units, water is being circulated by using pumps for cooling purpose. I would like to know will it be feasible to generate powerby installing generator set in return line of the system?

Ben Root's picture

Hello Sanjey,
The author of this article may reply to you. But in the mean time, I suggest you read the article here: especially Myth 1 about closed loop systems.

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