Alex Hort from the University of Plymouth has devised a system in which rain water descending a down pipe is captured and stored behind an internal 'dam' until its weight is sufficient to cause its sudden release. Each rush of water turns a small, plastic turbine that drives a micro generator installed in the pipe, providing eight minutes worth of electricity which is stored in rechargeable batteries.

This powers a proximity sensor and a porch lamp. When somebody approaches the front door of a house, the sensor detects them and turns on the light.

The idea was a "Specially commissioned university project" for the EDF Energy ideal home show at Earls Court, London, and is featured in the "Innovation Nation" area of the exhibition, which is open every day until April 13th. Visitors can both observe it and test it for themselves.

Energy saving is a major feature of this year's show.

Anyone interested in manufacturing the idea should contact Alex on either alexhort@hotmail.co.uk or 07974084669.