photo: David Shand/Creative Commons
A new study supported by Scotland's John Muir Trust, examines the potential electricity generation from wind power there and comes to the conclusion that a number of popular pro-wind talking points overstate the case.
Based on examination of existing wind turbine output between 2008 and 2010, the report found:
- Wind turbines generated on average just 24% of their rated capacity--an average figure of 30% is generally used when talking about potential power from a given project.
- Taking on the assertion that the wind is always blowing somewhere, the analysis found that there were 124 times when winds dropped so much that just 4% of expected output was generated. Low wind conditions occurred on average somewhere in the study area every 6.38 days for an average period of 4.5 hours. On four of the highest peak demand periods in the study period, wind output was between 2.51% and 5.51% of capacity.
The whole thing is presented by John Muir Trust as a quasi-scandal about wind power. Report author Stuart Young says in their press release,
It was a surprise to find out just how disappointingly wind turbines perform in a supposedly wind-ridden country like Scotland. Based on the data, for one third of the time wind output is less that 10% of capacity, compared to the 30% that is commonly claimed.
That is indeed an important stat to keep in mind, but is hardly eye opening for anyone who's looked at the individual output of the wind farms in Scotland or anywhere else. Furthermore, the 30% figure has always been rounded up slightly in estimates. Which isn't to state that sometimes projected output isn't overestimated. It clearly is.
The finding that there have been a number of instances of seriously low wind power output is another useful bit of data, and a very important one. But I'm not sure that it's a serious blow against wind either in general or against the general claim that the wind is always blowing somewhere or that periods of low wind are infrequent. If anything 'always' is an overstatement. Using 'most often' instead would allow some semantic wiggle room.
The report also highlights that the non-ability of the UK's pumped storage capacity to offset these periods of low wind. Which too is perhaps not as surprising as the public touting of the report by the John Muir Trust makes it seem. It just means that other storage methods need to be developed quickly. Even the most ambitious energy scenarios eliminating fossil fuels reference a completion date of a decade or fifteen years away. Only if by that time if electricity storage to offset natural periodic shortfalls in renewables is lacking does it become a practical problem--expansion of that storage needs to happen alongside expansion of renewables, as does transmission.
Here's the full report: Analysis of UK Wind Power Generation - November 2008 to December 2010 [PDF]