The energy potential of moving water has been harnessed for thousands of years, originally using water wheels to drive mills and machinery. Hydropower currently produces 2% of the UK's electricity needs. Whilst most of this comes from large dam projects, there is still hydropower potential in certain parts of the country.

Hydropower as a source of energy

Small-scale hydropower has been used from the earliest times of electricity generation. Sluices and dams of old mills were used to generate a few thousand watts locally. These systems died out with the introduction of large national distribution schemes. Now, small "micro hydro" is being looked at seriously again. With improvements in small generator technology, it is now quite feasible to produce a few tens of kilowatts of electricity form even with the lowest water "heads" of 2 - 3 metres. It's estimated that there is potential in the UK for about 200 MW of installed capacity at this level.

Any hydropower technology turns the potential or kinetic energy of the water into energy by means of a turbine. Turbines either use water 'dropped' from behind a dam or from natural 'run of the river' with no water storage reservoir.

The requirements of micro hydropower schemes are:

  • Good (or at least reliable) rainfall.
  • Adequate volumetric flow and/or water pressure (anything above a couple of metres of head). This determines the amount of power attainable. 
  • A water intake above a weir or behind a dam.
  • A water transport system, which will channel the water.
  • A flow control system.
  • A turbine and generator.
  • An outflow.

As with any small renewable energy scheme, micro hydro does not benefit from the economies of scale of a larger scheme. Also, as a general rule of thumb, capital costs rise as available head decreases.

Capital cost of a micro hydro installation

This varies widely, but is typically between £200 and £3,000 per kW capacity. This is a very rough figure and is highly dependent upon:

  • Degree of existing infrastructure, disused mill/weir etc. 
  • Willingness to assist manufacturer/installer.
  • Type of hydro resource available.
  • Type of hydropower system used.

A system below 10kW is probably not worth grid connecting, unless there's an existing grid connection. This sort of sized system would be better suited to battery charging or as a backup for a critical load, in place of a diesel generator, for example. Various consents and licences are required for a hydro project. These are generally dealt with by the Environment Agency and local planning authorities.

More information about hydropower and a list of suppliers.