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Energy and Climate Change written question – answered on 10th July 2013.

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Photo of Caroline Flint Caroline Flint Shadow Secretary of State for Energy and Climate Change

To ask the Secretary of State for Energy and Climate Change

(1) what estimate his Department has made of the de-rated capacity margins for electricity in each year since 1989 for which figures are available;

(2) what forecast his Department has made of the likely de-rated capacity margins for electricity in (a) 2013-14, (b) 2014-15, (c) 2016-17, (d) 2017-18 and (e) 2018-19.

Photo of Michael Fallon Michael Fallon The Minister of State, Department for Business, Innovation and Skills , Minister of State, Department of Energy and Climate Change

The information is as follows:

Historic margins

The following table shows the Great Britain capacity margin for 1999-2000 to 2011-12. Figures for 2012-13 will be available on 25 July 2013. For consistency with estimated future margins, this has been answered for Great Britain. However, unlike the figures in the estimated future margins, only renewables are de-rated in these figures (by factors set out in the 1989 Electricity Act for the calculation of declared net capacity for intermittent renewables), so margins are not comparable with the estimated future margins—the historical margins are likely to be higher.

  Capacity margin (GB de-rated major power producers capacity(1)/GB maximum demand) (percentage)
1999-2000 21.0
2000-01 23.5
2001-02 25.2
2002-03 14.0
2003-04 18.1
2004-05 20.3
2005-06 19.6
2006-07 26.9
2007-08 23.5
2008-09 27.5
2009-10 28.8
2010-11 36.8
2011-12 42.9
(1) Only wind, small hydro and solar PV capacity are de-rated in these figures, therefore they are not directly comparable with the estimate of future margins below. Source: Digest of UK Energy Statistics, tables 5.8 (GB capacity) and 5.10 (GB Maximum Demand), available at:

Estimated future margins

The Energy Act 2011 placed an obligation on Ofgem to provide the Secretary of State with a report assessing capacity margins into the future. On 27 June 2013 Ofgem published their 2013 Capacity Assessment covering the period from winter 2013-14 to winter 2018-19.

Their assessment was that de-rated margins over the period would be as follows:

  De-rated(1)capacity margin (percentage)
2013-14 6.25
2014-15 4.75
2015-16 3.81
2016-17 6.34
2017-18 8.91
2018-19 7.76
(1) All technologies have been de-rated to take into account their expected availability at times of system peak, therefore they are not directly comparable with the historical margins above.

More details on the Ofgem Capacity Assessment, including on the outlook for capacity margins in different scenarios, can be found in their report:

As required by the Energy Act 2011, DECC will publish a response to the Ofgem Capacity Assessment later this year.

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