Water power can be harnessed in many ways; tidal flows can be utilised to produce power by building a barrage across an estuary and releasing water in a controlled manner through a turbine; large dams hold water which can be used to provide large quantities of electricity; wave power is also harnessed in various ways. It is a technology that has been utilised throughout the world, by a diverse range of societies and cultures, for many centuries. Water can be harnessed on a large or a small scale - Table 1, below outlines the categories used to define the power output form hydropower. Micro-hydro power is the small-scale harnessing of energy from falling water; for example, harnessing enough water from a local river to power a small factory or village. This fact sheet will concentrate mainly at micro-hydro power.

Large- hydro


More than 100 MW and usually feeding into a large electricity grid

Medium-hydro


15 - 100 MW - usually feeding a grid

Small-hydro


1 - 15 MW - usually feeding into a grid

Mini-hydro


Above 100 kW, but below 1 MW; either stand alone schemes or more often feeding into the grid

Micro-hydro


From 5kW up to 100 kW; usually provided power for a small community or rural industry in remote areas away from the grid.

Pico-hydro


From a few hundred watts up to 5kW ,...
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