Hydropower is one of the most efficient renewable energy sources. It is particularly suited to small-scale applications typically being far cheaper per unit (kWh) of electricity produced than wind power or solar power.
Enormous hydro projects such as the 22.5GW Three Gorges Dam make all the news, yet many people see microhydro (<100kW), and especially picohydro (<5kW) as being very important, particularly for the developing world. Vietnam for example already has well over 100,000 picohydro turbines in action.
A 300 Watt pico hydro turbine can be purchased in Vietnam for as little as $20 and will meet the electricity needs of a whole family. There is no need in most cases for expensive battery storage since the power generation is constant 24 hours a day 365 days of the year. A complete pico hydro system including wiring, piping, and a suitable turbine housing can be set up for just a couple of hundred dollars very easily. There is no need for a dam or any expensive construction since these are run of river hydro systems.
Family-sized 200+ Watt Pico hydro generator units typically need just a 1 metre drop in water height and a constant water supply in order to generate power. A larger unit can be used to power a whole village when used in conjunction with energy saving light bulbs.
Here is a video which shows a low head (2.5-15 metre) Pico hydro project in a mountainous region of Nepal installed in an irrigation canal. This hydro project can generate up to 300 Watts for a nearby village at an efficiency of up to 73%. Energy efficient lightbulbs (CFL bulb) are supplied with the hydro power unit to make the most of the generated power.