The energy in falling water can be converted into electrical energy or into mechanical energy to pump water or grind grain. The amount of energy that can be captured is a function of the vertical distance the water drops (the head) and the volume of the water. One hundred cubic metres of water falling 10 metres (a low head application) represents the same energy potential as 10 cubic metres of water falling 100 metres (a high head application).
In the past, hydropower stations were often built as a part of large dam projects. Due to the size, cost, and environmental impacts of these dams (and the reservoirs they create), hydro developments today are increasingly focused on smaller-scale projects. Although the definition of small-scale varies, only projects that have less than 10 megawatts (MW) of generating capacity are considered here. This definition also includes mini-hydro (<1 MW), micro-hydro (<100 kilowatts, or kW), and pico-hydro (<1 kW).
