There is some dispute over the necessary amount of reserve or backup required to support the large-scale use of wind energy due to the variable nature of its supply. In a 2008 submission to the House of Lords Economic Affairs Committee, E.ON UK argued that it is necessary to have up to 80–90% backup. Other studies give a requirement of 15% to 22% of installed intermittent capacity. National Grid which has responsibility for balancing the grid reported in June 2009 that the electricity distribution grid could cope with on-off wind energy without spending a lot on backup, but only by rationing electricity at peak times using a so-called "smart grid", developing increased energy storage technology and increasing interconnection with the rest of Europe. In June 2011 several energy companies including Centrica told the government that 17 gas-fired plants costing £10 billion would be needed by 2020 to act as back-up generation for wind. However, as they would be standing idle for much of the time they would require "capacity payments" to make the investment economic, on top of the subsidies already paid for wind. In 2015/2016 National Grid contracted 10 coal and gas-fired plants to keep spare capacity on standby for all generation modes, at a cost of £122 million, which represented 0.3% of an average electricity bill.