Three completely independent reports on the wind variability issue appeared in June and July 2009, all with the same message: the variability of wind needs to be taken into account, but it does not make the grid unmanageable; and the additional costs, which are modest, can be quantified.
National Grid’s “Operating the Electricity Transmission Networks in 2020” was a consultation document and sought views on their assessment of the generation mix in 2020 and the way that the system would operate with around 30 GW of wind capacity. It covered technical and market issues.
National Grid estimates that this level of wind generation will increase requirements for Short-Term Operating Reserve by 6.5 GW (above the 2009 level of 4 GW), at an additional cost of around £418 million per annum.
This corresponds to around £5.4/MWh of wind generation and is consistent with other recent estimates for this level of wind energy generation.
However, National Grid suggests that these estimates could come down by nearly 40% with better wind forecasting techniques.
They also list a number of technologies that might be available to provide Short-Term Operating Reserve, including storage and electric cars and note that “Smart Meters” may also play a part in smoothing the variations in the demand profile.
The report notes that improved interconnection between Great Britain and Northern Europe “has the effect of sharing intermittency across a wider area and reducing its impact.” However, they suggest that it is important to understand likely interactions with the European electricity markets.
David Milborrow’s report, “Managing Variability” was commissioned by the World Wildlife Fund, Friends of the Earth and Greenpeace UK. Its objective was to summarise and quantify the issues surrounding variability and also identify mitigation measures that may be developed.
The author argues that wind variability issues cannot be discussed in isolation and need to be set in context alongside the variability of consumer demands and the intermittency associated with thermal plant breakdowns.
Sudden shocks, such as the “trip” of a large generating Nuclear, Natural Gas or Coal unit, which can result in the loss of anything up to 1200 MW in the UK, do not occur with wind energy.
Moreover, the variability of wind power is not a totally unknown and unpredictable quantity and the author presents data that quantifies both the standard deviation and the maximum power swings that occur on one hour and four hour timescales.
The report quantifies the additional costs of variability due to all causes (additional short-term reserve, extra backup for peak demand periods, and constraints when wind production exceeds consumer demand). It suggests that these costs, with 40% of the electricity supply coming from wind, might add about 5.5% to domestic electricity bills.
The report includes a detailed evaluation of a number of studies that have been completed on the issue of the “capacity credit” of wind and shows that these have all yielded very similar conclusions: the capacity credit is roughly equal to the average power at low wind energy penetration levels, falling to about half this level when the electricity supply is 40% from wind.
The report identifies 10 possible mitigation measures, and these are almost identical to the list produced by National Grid, discussed in the previous paragraph.
The “Impact of Intermittancy” report from Pöyry, the Oxford energy consultants, is a public summary of a much larger report produced for System Operators, utilities and developers in Britain and Ireland.
The focus of this report is principally concerned with how the electricity markets in the two countries are likely to behave when there are substantial quantities of wind on both systems.
The estimates of additional reserve are similar to those in the other two reports and one of the conclusions is that the electricity market in Britain may be less suited to the assimilation of wind than the electricity market in Ireland.
[ This article was authored by Claverton Energy Research Group professionals. ]