If you have a suitable site, harnessing the energy in a stream or creek can be the most cost-effective way to make renewable electricity. Compared to the sun and wind’s variability, a stream’s flow is relatively consistent; making microhydro-electric system output the most predictable of all the renewable energy (RE) electrical systems. Hydro resources are also the most sites specific, since your property must have a usable water source. If you are one of the lucky few with a stream running down your hillside, it’s the resource to assess first.
Hydropower is based on simple concepts. Moving water turns a turbine, the turbine spins a generator, and electricity is produced. Many other components may be in a system, but it all begins with the energy already within the moving water.
Water power is the combination of head and flow. Both must be present to produce electricity. Consider a typical hydro system. Water is diverted from a stream into a pipeline, where it is directed downhill and through the turbine (flow). The vertical drop (head) creates pressure at the bottom end of the pipeline. The pressurized water emerging from the end of the pipe creates the force that drives the turbine. More flow or more head produces more electricity.
Head is water pressure, which is created by the difference in elevation between the water intake and the turbine. Head can be expressed as vertical distance (feet or meters), or as pressure, such as pounds per square inch (psi). Flow is water quantity, and is expressed as "volume per time," such as gallons per minute (gpm), cubic feet per second (cfs), or liters per minute (lpm).
Unlike larger forms of hydroelectric power, micro hydro does not have as many lasting effects on the environment. While larger hydroelectric power stations often dam major rivers to create huge reservoirs which forever change the landscape, no such reservoir is needed with micro hydro power generation. If a reservoir is needed, micro hydro often makes use of natural pools found on a stream. However, in most cases, reservoirs are not needed at all.