* Major utilities, manufacturers sign up to partnership
* E.ON awards offshore cable contract to Balfour Beatty
* Two UK biomass plants reach milestones
LONDON, April 26 (Reuters) - More than twenty companies have signed a partnership agreement to turn the North Sea into a major renewable energy hub focusing on offshore wind power, Britain's Prime Minister David Cameron is to announce on Thursday.
Major utilities, such as Britain's Scottish Power and Norway's Statoil, manufacturers from Siemens to Gamesa and supply chain companies are supporting the initiative, provisionally named Norstec.
"Our commitment and investment in renewable energy has helped to make renewable energy possible. Now we have a different challenge. We need to make it financially sustainable," Cameron will tell ministers from 23 countries who are attending a two-day clean energy summit in London.
Further details about the operations of the network will be releaved at an offshore wind conference in London in June.
Britain has an ambitious target of installing 18 gigawatts (GW) of offshore wind power capacity by 2020, compared with around 2 GW in operation in British waters at the moment.
German utility E.ON is also on Thursday expected to award a 736 million pound cable installation contract to British construction firm Balfour Beatty to connect its Humber Gateway offshore wind farm to the electricity grid.
The 230-megawatt (MW) wind farm will be located 8 kilometres off the coast of East Yorkshire and its 73 turbines will produce the equivalent of electricity used in 150,000 homes.
Two UK biomass power plants also reached major milestones on Thursday, with Helius Energy close to securing a finance deal to fund its 300 million pound Avonmouth plant and a construction start at the ECO2 38-MW biomass plant in Sleaford.
British Energy and Climate Change Minister Greg Barker said earlier this week Britain would also sign clean energy cooperation agreements with Brazil, Germany, South Korea and the U.S. as part of the international summit.
On Monday, Britain announced a partnership with the U.S. to support the development of floating wind turbines which can tap stronger wind forces.