Micro hydro power is probably the least common of the three readily used renewable energy sources, but it has the potential to produce the most power, more reliably than solar or wind power if you have the right site. This means having access to a river or creek that has a high enough flow to produce useable power for a good part of the year.
Many creeks and rivers are permanent, ie, they never dry up, and these are the most suitable for micro-hydro power production.
A micro hydro turbine can take several forms, the most widely recognized of which would be the water wheel, used extensively for grain grinding up until this century. Waterwheels are still used in some situations that do not require a fast-spinning turbine, such as for pumping water. However, other type of turbines have become quite common.
The most common of these newer turbines is the Pelton wheel, which is basically a series of cups attached to a hub. A jet of water is aimed at the cups, and the resulting force on the cups causes the turbine to spin.
Other types of turbines include the Turgo, Crossflow and various axial flow turbines, where the shaft through the center of the turbine runs in the same direction as the water flow, much like a boat propeller.
Water turbines have many advantages over solar panels or wind turbines, the most obvious of which is that they produce power continuously, 24 hours per day. However, they also have some associated problems or requirements. The most important of these is correct siting of the turbine and associated equipment so as to cause the least environmental damage as possible. Placing a large concrete dam across a creek or river can do considerable damage to the surrounding ecology. A general rule of thumb is to not divert more than 20% of the water flow of the creek through your turbine, and to return any diverted water back to the creek just below the turbine.
