Old watermills—Britain's new source of energy?

Britain's 20 000 disused watermills could be brought back to life as micro-hydrostations generating up to 1000 MW of electricity thanks to a renewed interest in waterwheels, particularly in Germany. Though slightly less efficient than modern low-head turbines, both overshot and undershot waterwheels are much cheaper to build, install and maintain and can operate in a wider range of flow conditions and with a head as little as 0·5 m. Archimedian screws working in reverse have also proved very efficient and durable low-head generators. This paper reviews the latest developments in Germany and the potential for application in the UK.