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Microhydropower Turbine, Pump, and Waterwheel Basics

August 16, 2013 - 3:58pm


A microhydropower system needs a turbine, pump, or waterwheel to transform the energy of flowing water into rotational energy, which is then converted into electricity.



There are two general types of turbines: impulse and reaction.

Impulse Turbines



Illustration of a Pelton wheel, which has double-cupped buckets attached to the outside. The entire wheel is housed in a round metal casing. At one end of the casing is a pipeline, which funnels into a pressurized pipeline with a narrow nozzle. The water sprays out of the nozzle in a jet, striking the double-cupped buckets attached to the wheel. The impact of the jet spray on the curved buckets creates a force that rotates the wheel, and the water is then expelled through another pipe on the other side of the casing

Pelton wheels, like this one, can be purchased with one
or more nozzles. Multi-nozzle systems allow more water
to impact the runner, which can increase wheel output.


The Turgo impulse wheel is an upgraded version of the Pelton. It uses the same jet spray concept, but the Turgo jet, which is half the size of the Pelton, is angled so that the spray hits three buckets at once. As a result, the Turgo wheel moves twice as fast. It is also less bulky, needs few or no gears, and has a good reputation for trouble-free operation. The Turgo can operate under low-flow conditions but requires a medium or high head.

Another turbine option is called the Jack Rabbit (sometimes referred to as the Aquair UW Submersible Hydro Generator). The Jack Rabbit is a drop-in-the-creek turbine that can generate power from a stream with as little as 13 inches of water and no head. Output from the Jack Rabbit is a maximum of 100 watts, so daily output averages 1.5–2.4 kilowatt-hours, depending on the site.

Reaction Turbines

Reaction turbines, which are highly efficient, depend on pressure rather than velocity to produce energy. All blades of the reaction turbine maintain constant contact with the water. These turbines are also often used in large-scale hydropower sites.

Because of their complexity and cost, reaction turbines aren't usually used for microhydropower projects. But one exception is the propeller turbine, which comes in many designs and works much like a boat's propeller.



Conventional pumps can be used as substitutes for hydraulic turbines. When the action of a pump is reversed, it operates like a turbine. Because pumps are mass produced, they can be found more readily than turbines. Pumps are also less expensive. For adequate pump performance, however, a microhydropower site must have fairly constant head and flow. Pumps are also less efficient and more prone to damage.

