U.K. energy regulator Ofgem on Wednesday launched a £400 million tender for linking offshore wind farms in the North Sea to Britain's national power grid. Ofgem is calling for firms to construct high-voltage transmission links to connect the Westermost Rough wind farm owned by WMR Limited, part of DONG Energy, and the Humber Gateway wind farm owned by E.ON., to the grid, Ofgem said in a statement. The two sites have a combined capacity of 425 megawatts, while the successful bidders will receive a guaranteed revenue stream for 20 years, Ofgem said. Offshore wind farm developers are required by the regulator to open their transmission assets for tender to encourage competition and lower prices.