Micro-hydro

Hydroelectricity is electricity generated by
the production of power through use of the gravitational force of falling or flowing water.

Small in-flow hydro is relatively cheap and can be cost effective especially where it meets local electricity demand. Making a profit will depend on the flow and head available, the cost of the installation, and the cost of grid connection.

The following equation will help you figure the profitability of your plant: Power (watts) = Head (m) x Flow (litres/sec) x 9.81 (gravitational constant ‘g’). A typical water to wire efficiency is around 70 per cent, so you should multiply the result by 0.7 to get the actual amount of electricity that you can expect from the site.

Most sites vary considerably in flow between winter and summer, reflecting the differences in rainfall. It is important to make sure that the flow is sufficient to run the turbine, sometimes installing two turbines will allow you to extract the maximum capacity when the water flow allows.

For low head systems, costs may be in the region of £4,000 per kW installed up to about 10kW and would drop per kW for larger schemes. For medium heads, there is a fixed cost of about £10,000 and then about £2,500 per kW up to around 10kW - so a typical 5kW domestic scheme might cost £20-£25,000. Unit costs drop for larger schemes.

Further information:

• See the Environment Agency’s Hydropower handbook.
• See the Environment Agency's mapping work on available hydropower sites in the UK and their feasibility
• Read the British Hydropower Association Mini Hydro step-by-step guide. Tel: 01202 880333