A 5.5 kW screw turbine has been installed next to the weir at Benjafield Farm. The site is on Shreen Water – a tributary of the River Stour – between Mere and Gillingham in Dorset.

The installation of this renewable electricity generation is estimated to generate 28,000 kWh/yr saving 13 tonnes of carbon dioxide a year and provides for some of the high electrical demand at this cattle farm. This farm diversification provides income to the farm from the Feed in tariff and sales of electricity. A screw turbine was chosen to match the low head, high flows and requirement for fish protection at this site. The rated flow of the turbine is determined by the 1.8 m head and flows available. To comply with the Environment Agency Good Practise Guidelines, a 1.0m diameter turbine, taking a maximum flow of 0.320m3s was chosen. The project included stabilisation of the west bank and construction of a timber housing for the gearbox, generator, grid connect and control unit.

Extensive negotiation with the Environment Agency was required to ensure that the scheme design and methods of construction complied with the environmental standards expected to achieve the necessary Abstraction License and Flood Defence Consent. It was decided to install the turbine in a new excavation next to the existing weir. A V shaped notch in the weir has been provided to enable down river fish passage. The grid connection is arranged so that electricity generated supplies the needs of the site, only exporting to the grid when there is a surplus.

The total project budget was £70,000. Sowing Seeds provided £31,213 but the process from initial agreement to receipt of the grant took 3 years. This is one of three hydropower projects in the area in receipt of the grant, all using different hydro turbine technologies.

There are numerous old mill sites and other potential hydropower sites in Dorset. The Feed in Tariffs, sales of electricity and avoided import of electricity make development of these sites financially attractive. Project management is not beyond the scope of a talented amateur but the complexity of the design and license application process means that expert advice is usually required. It is intended (and required under the conditions of the grant received) that the project will be well monitored, documented and publicised to enable other Dorset hydro projects to learn from the experience gained in developing and maintaining hydropower at Benjafield Farm.

The project was developed with Potent Energy – find out more at: www.potenergy.co.uk.

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Thanks to Sustainable Dorset for project details