During the past decade, microhydropower has made a quantum leap in technology that makes it affordable for homeowners with access to the flow of only a few quarts of water per second. Advances include low-priced and surprisingly compact turbine-alternator units, dropping prices for small inverters and charge controllers and more efficient battery storage.

Microhydropower systems are generally defined as less than 100 kilowatts (some microturbine systems produce 50 to 1,500 watts) and are being installed for both off-grid applications and as a supplemental power source for the grid-connected.

For anyone who has access to a brook, a stream or a small spring, a microhydropower installation could make sense. What is essentially necessary is that the water source or intake be at a higher elevation than the turbine. Intake water goes into a pipe (called a penstock in hydro) and travels downhill to drive a turbine. Even a garden-hose-sized flow can provide sufficient pressure to drive a waterwheel in a miniature turbine.

Most micro units combine a turbine joined to an alternator with a footprint of approximately 12-by-12 inches and weighing 50 to 60 lbs. Water enters the turbine through nozzles ranging in diameters from 1/8 to of an inch.

Depending on the model, there can be one, two or four nozzles that drive a bronze, cupped waterwheel of approximately 4 inches in diameter that is mounted in a metal housing. Permanent magnet alternators generate three-phase AC variable frequency power, which is converted to DC at the generator. They are designed as 12-, 24- or 48-volt battery chargers and charge 24 hours per day. DC power can be drawn from batteries as needed or inverted to AC for household use. There also are small units that produce AC without an inverter by using an impeller to backfeed a centrifugal pump, which drives an AC motor.

As long as water runs 24/7, grid-connected buildings can build net-metering credits or run the meter backward. As little as 5 gallons per minute falling 200 feet through a pipe can supply enough power to comfortably run a small household.

The cost of a microhydro system is conditional, but talking with an expert such as Richard Buttner, owner of NoOutage.com, can put you in the ballpark. Buttner is a licensed electrical engineer and knowledgeable about all things microhydro.

“We get a lot of people who contact us who have a pond or small stream and they think they can power their house, but when you actually plug in the numbers you find out that you can only get 50 or 100 watts. But if you have enough head pressure or flow, it’s far better than wind or solar as a dollar-for-dollar investment, with a return on investment several times greater,” Buttner said.

NoOutage.com has a calculator on its Web site that can help someone determine how much hydro power can be generated.