Published in The Utilities Journal, July 2004, pages 37-39.
“Denmark has installed 3,100 MW of wind turbine capacity to date, which is in theory capable of generating 20% of the country’s electricity demand. Of that capacity, 2,374 MW is located in western Denmark (Jutland and Funen). The statistic is misleading because it implies that 20% of Denmark’s power is supplied continuously from its wind capacity, but the figure appears to be a promotional statistic rather than a factual representation of the supply pattern.
“Jutland has cable connections to Norway, Sweden and Germany with a capacity of 2,750 MW. In other words, it has the means of exporting all of its wind production. The 2003 annual report of Eltra, the western Denmark transmission company, suggests an export figure of 84% of total wind production to these countries in 2003, with figures that ramped up rapidly over previous years as Denmark found that it could not absorb wind output into the domestic system.”
“There is no CO2 saving in Danish exchange with Norway and Sweden because wind power only displaces CO2-free generated power. When the power is consumed in Denmark itself, fluctuations in wind output have to be managed by the operation of fossil-fired capacity below optimum efficiency in order to stabilise the grid (ie, spinning reserve). Elsam, the Jutland power generator, stated as recently as May 27th at a meeting of the Danish Wind Energy Association with the Danish government that increasing wind power does not decrease CO2 emissions. Ireland has drawn similar conclusions based on its experience that the rate of change of wind speed can drop faster than the rate at which fossil-fuelled capacity can be started up [emphasis added]. Hence spinning reserve is essential, although it leads to a minimal CO2 saving on the system. Innogy made the same observation about the operation of the UK system [D. Tolley, presentation to Institute of Mechanical Engineers, January 2003].
“The result is that, while wind-generated power itself is CO2-free, the saving to the whole power system is not proportional to the amount of fossil-fuelled power that it displaces. The operation of fossil-fired capacity as spinning reserve emits more CO2/kWh than if the use of that plant were optimised, thus offsetting much of the benefit of wind.”
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