Dorechester-based Hallidays Hydropower (www.hallidayshydropower.com) has installed an 11.5-tonne Archimedes-screw turbine at Bladon Lake dam on the River Glyme in Woodstock.

The 32ft by 7ft screw, positioned below a waterfall, will generate enough electricity to power 20 homes on the Blenheim Palace estate.

The scheme, which was delayed by three months because of wet weather, is expected to save the Oxfordshire estate £18,000 a year in electricity costs; it should be up and running in August.

It took 21/2hr for eight workmen to install the screw. Hallidays chief engineer Henry Reily-Collins, who worked on the project for four years, admitted he was “nervous” about damaging the dam, which dates from the 18th-century landscaping of the park.

He said: “To see it finally in place and know that it fits in with the landscape harmoniously was a relief.”

Electricity is generated by the rotation of the screw, which has a 100-year lifespan. The steel tube encasing the screw has three glass windows, so it is possible to watch the screw turning.