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 (17)

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

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

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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