Wind turbines tested at Gunfleet Sands off Essex coast
13 September 2013 Last updated at 18:14 BST
Two prototype wind turbines, the biggest in the world, are being tested off the Essex coast.
The six megawatt (MW) turbines can generate almost twice as much electricity as the existing ones and have been built at Gunfleet Sands near Clacton.
The have been made by Siemens and installed by Dong Energy.
The Department of Energy and Climate Change says they are more cost effective and efficient than the turbines currently used.