LONDON (Reuters) - British wind farms may be shut down about 38 days per year by 2020 to avoid power transmission overload at times of weak demand and high wind speeds, UK energy network operator National Grid said on Monday. Britain is expected to increase wind power capacity seven-fold by 2020 to 26.8 gigawatts (GW), according to National Grid data, which would put additional strain on the transmission network.
National Grid's challenge is to incorporate rapidly growing renewable energy capacity into the network from wind and solar plants, whose output is more intermittent and thus more difficult to predict than that from thermal plants.
"It will become increasingly necessary to restrict the output from wind generation onto the system to ensure sufficient thermal capacity is synchronized," National Grid said in a 2020 transmission system report published on Monday.
Based on historic data, wind turbines will have to be switched off for 38 days every year when wind power production exceeds 35 percent of installed wind capacity and demand falls below half the levels seen at peak time, National Grid said.
In Germany, where more than 25 GW of wind capacity is already in place, high wind speeds coinciding with low power demand, for example overnight during summer time, have caused negative wholesale power prices as producers are forced to sell renewable energy to the grid.
Britain's network operator said the development of power storage facilities will be an important tool for managing renewable energy supply as they can act as "sinks" for wind and solar power.
"National Grid believes that suitable funding streams should be introduced to support innovative storage technologies to bring them to a point where they are made viable."
(Reporting by Karolin Schaps, editing by Jane Baird)