Water power

Wallbridge Mill is one of the smallest micro-hydro stations supplying the National Grid. The River Frome, which runs through the South Mill, produces enough power to keep about four conventional houses as well as the all-electric building.

It does this using the 1908 Canadian turbine mothballed when animal feed production stopped. The turbine has been totally restored by Malcolm Cooper, one of 11 remaining British millwrights, and Leslie Graham-Gleed (right). The power now goes directly through the central shaft to a generator (an asynchronous motor with gearbox). The power is synchronised with the National Grid through a load controller. The mill has first call on the power, and the surplus goes to the Grid.

How much electricity is produced is entirely dependent on local rainfall. The River Frome rises only six miles away, at Witham Friary, and the volume of water in the river totally reflects local weather conditions. In winter, the turbine will generate 11kilowatts an hour (kWh) for 24 hours. In the summer, there are spells of non-production.

This year, the mill expects to generate around 35,000 kWh. As a renewable source, there is a premium paid for the power by Southern Electric, but it isn't a fortune: the payback period for the renovation costs and equipment is about 10 years.