Hydro-power produces one fifth of all the world's electricity. Many former water wheels are still visible on streams and rivers today that once harnessed for grinding grain or in factories.
Small hydro stations have no dams - they are 'run of river' and make a minimal impact on the environment. Water is returned downstream at the same temperature and composition as extracted. Screening of the inlets and a residual flow on the river ensure that wildlife is protected with only clean green electricity produced as a result.
The theoretical power available in a river is the flow of the water times the height, or head, the water can fall. The water turns a hydro turbine connected to a generator, which produces electricity from mechanical energy. The green electricity is sent to the local network for distribution. Even relatively flat areas can generate electricity from local streams and rivers.
Developing hydro schemes requires an assessment of the resource available and then planning permission from the local authority as well as the Environment Agency.