Wind Power in The United Kingdom - Variability and Related Issues

Variability and Related Issues

Wind-generated power is a variable resource, and the amount of electricity produced at any given point in time by a given plant will depend on wind speeds, air density, and turbine characteristics (among other factors). If wind speed is too low (less than about 2.5 m/s) then the wind turbines will not be able to make electricity, and if it is too high (more than about 25 m/s) the turbines will have to be shut down to avoid damage. If this happens during a winter cold snap, when winds are calm over large regions and electrical demand reaches its highest levels of the year, other power sources must have the capacity of meeting that entire demand. Three reports on the wind variability in the United Kingdom issued in 2009, generally agree that variability of the wind does not make the grid unmanageable; and the additional costs, which are modest, can be quantified. In the United Kingdom, demand for electricity is higher in winter than in summer, and so are wind speeds.

While the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable. Studies by Graham Sinden (2009) suggest that, in practice, the variations in thousands of wind turbines, spread out over several different sites and wind regimes, are smoothed, rather than intermittent. As the distance between sites increases, the correlation between wind speeds measured at those sites, decreases.

A Scottish government spokesman has said electricity generated by renewables accounted for 27% of Scotland's electricity use. On the night of 5–6 April 2011, the wind in Scotland was high, it was raining heavily, which also created more hydroelectricity than normal. The grid became overloaded preventing transmission of the electrical power to England, as a result the electrical wind power generation was cut. Wind farms operators were paid compensation known as "constraint payments" as a result (a total of approximately £900,000) by the National Grid, estimated at twenty times the value of electricity that would have been generated. A spokesman for the Department for Energy and Climate Change (DECC), described the occurrence as unusual, and noted it demonstrated a need for greater energy storage capacity and better electrical power distribution infrastructure. The payment of 'constraint payments' to wind energy suppliers is one source of criticism of the use wind power, and its implementation; in 2011 it was estimated that nearly £10 million pounds in constraint payments would be received, representing ten times the value of the potential lost electricity generation.

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. 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.