Scottish and Southern Energy (SSE) and Viking Energy -- a company owned by Shetland Islands Council -- are joining forces to develop a 600 MW wind farm on the Shetland mainland. The parties are to combine their separate plans for large wind farms, each of up to 300 MW capacity. The two companies have signed an agreement to work towards a joint venture development. Merging their projects will allow the companies to manage all the issues, such as environmental assessment, as part of a single development. It will also improve the economic and technical credibility demanded of developers to justify energy regulator Ofgem approving construction of a sub sea electricity cable to connect the islands to mainland Scotland. The cable would be built by Scottish Hydro-Electric Transmission Ltd -- also a subsidiary of SSE -- which owns the grid network in the north of Scotland. Shetland is the windiest part of the UK. The wind farm could expect a load factor of up to 50%, meaning it would produce electricity at close to its maximum capacity for around half of the time, making it the most productive wind farm in Europe. "Combining our proposals with Viking Energy should lead to a larger and more coherent development on the islands," says Ian Marchant, chief executive of SSE. "Despite the many challenges, I am optimistic that we will be able to demonstrate the viability of an undersea cable to the mainland."