Don’t overlook hydropower potential

Since its installation in 2009, the Archimedes screw turbine at Hainbury Mill Farm has been generating about 80,000kWh a year, worth £16,000 in FiT payments, plus the value of any electricity exports and import savings.

By Brian Shingler, secretary, South Somerset Hydropower Group

In the drive for renewable energy, hydropower does appear to have been slightly neglected compared with other technologies. Even so, UK hydro now accounts for nine percent of installed generating capacity under Feed-in Tariffs and new schemes are going in all the time.

Hydro has the capability of operating 24/7 throughout the year, and with a greater output in the winter, when electricity demand is higher. So load factors of up to 40-50% of theoretical annual outputs are possible.

But, of course, you do need a river. Most farmers would be looking at “run of river” schemes, rather than storage, where the turbine size is matched to the natural flow of the river. Power output is directly proportional to flow (cubic metres/second) and head (metres) – the fall in the river from the upper level to a lower level. As a very rough guide, the potential electrical power output (kW) equals flow x head x 5.0, once efficiency losses in the turbine and generator are taken into account.

Though there is the potential in upland areas for new weirs, in lowland Britain most potential sites will be based on existing weirs, where the head can be easily measured. Flow is slightly more difficult, but there are standard formulae for calculating the instantaneous flow over a weir, depending on its width and the depth of water flowing over. However, it is variation in flow that is more important, with chalk streams, for example, being less variable than other rivers. The National River Flow Archive has many years’ data from gauging stations on rivers throughout the UK. Corrections can be made for any particular weir site according to its catchment area compared to the catchment area of the gauging station.

Technology choice

A range of turbines is commercially available, including the Pelton wheel, crossflow, Francis, Kaplan and, more recently, the Archimedes screw. The best type of turbine for any particular site will depend on the head and flow, the physical constraints of the site and other factors such as trash cleaning and fish passage.

New hydro generators are now eligible for a Feed-in-Tariff of 18.7p/kWh, if between 15kW and 100kW output, and 20.9p/kWh for 15kW output or below. This is in addition to 3.1p/kWh for electricity exported to the grid, and, if applicable, a greater sum on cost-saving on imported electricity. If new hydro plants (under 50kW) are commissioned before 1 April 2012 they do not need to be accredited under the Microgeneration Certification Scheme, but instead will be accredited under the simpler ROO-FIT process. There is also the opportunity to renovate existing historic turbines and waterwheels and claim FiTs.


New hydro schemes, unless the water is taken from above a weir and discharged directly into the weir pool, will need an Abstraction Licence from the Environment Agency. Other consents such as Flood Defence Consent, Impoundment Licence, Fish Pass Approval and Fish Screen Regulations may also need to be addressed. In any case it is a good idea to talk to the EA at a very early stage to establish what consents will be needed.

Hydro schemes are generally viewed by the public as being the most environmentally-friendly of all renewable technologies. Local people are proud that the power of their local river is being harnessed to produce renewable electricity.

The development of hydro on any particular site is very site specific and the site owner is likely to need a good consultant and installer to advise on the best equipment for their site and guide them through the various processes involved. There is a list of MCS-approved installers on the MCS website, and also a list of manufacturers registered with MCS under transition arrangements.

Capital costs of a hydro project are likely to be in the range of £4,000-6,000 per installed kW, but this will vary very greatly depending on the civil works already in place on the site. Smaller sites will generally have higher costs per installed kW.

Even though an excellent consultant may have been engaged, that does not mean the site owner should not research the best option themself. The best starting point is undoubtedly the mini-hydro guide on the British Hydropower Association website. The Hydropower Good Practice Guidelines on the EA website is also essential reading.

But there is no substitute for visiting hydro sites that have already been developed and discussing with the site owners their experiences and the benefits they have achieved.

The South Somerset Hydropower Group was formed in 2002, with the aim of exchanging information between owners of potential sites throughout the area. We now have eight hydro sites in operation – some generating at up to 80,000kWh a year. Since 2002 other hydropower groups have formed around the country.

In association with the Mendip Power Group, the SSHG will be running a hydropower tour over the weekend of 15 and 16 October. The tour will include visits to nine successful sites operating in the area, all with very different installations to fit their particular site.

For more details see our website

Other useful contacts

National River Flow Archive: 01491 692599

Microgeneration Certification Scheme: 0207 090 1082

Environment Agency: 03708 506 506

British Hydropower Association: 01258 840934

Feed-in Tariffs