The sun lifts water up from the sea to the hills. Gravity pulls it back down again. This is the "hydrological cycle". Global warming is causing it to gradually speed up.

A hydro generator harnesses that gravitational energy to spin a turbine. A micro, or 'pico', hydro turbine can be used to power the lights and appliances in a home and provide heating as well. Excess power can also be fed back into the national grid (to maximise your gains and thus reduce the payback period, we recommend you switch suppliers to provide you with an export tariff, such as that provided by nPower or Good Energy.)

The important requirements are a fairly reliable water flow and a reasonable 'head' of water pressure, or steep drop, preferably more than 10 metres, from a weir or dam to a turbine site near the building.

A power-head-flow graph is provided below, which you could use to estimate the yield from your site:

The feasibility of hydro systems is very site specific and advice should be sought from a specialist before permission and a licence sought from the Scottish Environment Protection Agency (SEPA).

With these hurdles crossed, hydro power can be the most cost-effective of all renewable energy systems, in spite of its higher maintenance requirements. Until at least 2015, the UK government will pay a few pence per unit generated under a system called the Renewables Obligation. This sum can adds value to that saved by the generation of 'free' energy.

Further information about system design, accredited equipment and installers can be found via the adjacent links.

Glenscorrodale Hydro Feasibility Study for Rokpa Trust

See EST factsheet.

For further information on SCHRI grants see www.est.co.uk/schri. 

Further information can also be found at the british hydropower association website.

Accredited installers and accredited equipment.