Hydropower renewable electricity generation project at Bindon Mill in Dorset.

Nature of Prioject
A 20 kW screw turbine was installed at the historic mill site of Bindon Mill. The site is on the River Frome near Wool on the Lulworth Estate. The estate has a record of good environmental stewardship. The installation of this renewable electricity generation is estimated to generate 77,000 kWh/yr saving 40 tonnes of carbon dioxide a year making the site a net exporter of electricity to the grid and providing an income to the Lulworth Estate 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 flows available and the limitations imposed by the grid connection. At this site, Scottish and Southern Power stated a maximum of 20 kW could be put into the grid. To comply with the Environment Agency Good Practise Guidelines, a 2.2 m diameter turbine, taking a maximum flow of 2.080 m3s was chosen.

The project included improvements to the existing fish ladder around the mill to facilitate better passage of salmon and trout for this environmentally important river. The turbine channel and turbine house were sensitively designed to blend well with existing building at this historic mill site.

Extensive negotiation with the Environment Agency, Natural England and Purbeck District Council was required to ensure that the scheme design and methods of construction complied with the environmental standards expected to achieve the necessary Abstraction License, Flood Defence Consent and Planning Consent.

It was decided to install the turbine in a new channel between the river and the exit to the fish ladder so that fish attracted to the turbine outflow would be able to make their way up the improved fish ladder. The fisheries research centre at East Stoke have installed fish counters to monitor the effects. To get the very heavy excavation and turbine delivery vehicle to site required the construction of two temporary bridges across the river and a parallel channel.

The turbine house above the top of the turbine houses a grid connect and control box that controls the flow of water through the turbine so that there is always enough flow in the river and fish ladder to ensure that fish can move up and down river. The grid connection is arranged so that electricity generated supplies the needs of the site owner’s residence, only exporting to
the grid when there is a surplus.

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.

For more information on this project visit the website at http://www.potenergy.co.uk/bindon_mill.php.

This story was provided by Sustainable Dorset, the website for DA21: www.sustainabledorset.org.uk/community-energy.