Friday, 8 November 2013

Do wind turbines reduce overall carbon emissions?

A little while ago, some friends asked my views on an article by Andrew Walker in the Highland and Perthshire News claiming that increasing our wind farms capacity does not have the desired effect of decreasing our carbon emissions. Now as I have stated before I am generally pro-wind so you should be careful to judge the merits of my arguments carefully. Very briefly, he says that wind power does not reduce the energy intensity of the electricity grid because it needs backup; also the carbon emissions from building wind farms are huge especially when they are built on peat. I do agree with his arguments about the peat: they originate from a letter in the Nature which is an excellent journal [1]. However, his other arguments are confusing and misleading.

Incidentally the newspaper article reports that Andrew Walker is a retired scientist. This is true - he was a professor of botany at West of Scotland Agricultural College (from private correspondence).

Backup requirements.

Walker states that because wind power is intermittent it '... must therefore be backed up by conventional power stations, which must be kept running to be available at short notice. In this back up mode they are using fuel inefficiently and the CO2 emitted is directly attributable to the wind farms.' This is a clear description of the sorts of backup the industry calls Fast Reserve (2 minute notice) or Short Term Operating reserve (STOR - 20 minute notice). For these, power stations are kept running but idle so they can be spun up quickly - spinning reserve. They are needed even without wind generation because of the variability of demand. Adding wind capacity increases the requirement for spinning reserve - estimates vary as to how much. Walker's summary article suggests that backup would be required for 80%-100% of wind capacity. However, this figure comes from a report by E.ON [2] and refers to a different sort of backup - the capacity needed for days when - as predicted by weather forecasters - there is little wind. When this happens there is plenty of time to bring power stations into production so they do not need to be constantly idling.

In his longer article, Walker quotes a study by UKERC [3] as requiring 20-32% of wind capacity as 'additional back-up capacity and system balancing reserves.' Walker claims this is a biased study because it comes from academia and is less reliable than the industry view from E.ON. Be that as it may, his report is similarly confusing  because in the UKERC report only 5-10% was for system balancing and the rest for longer notice backup.

Walker also states we have no capacity for large scale storage, which is true at the moment but there are many options under development. (see Dealing with Excess Wind)

Changes in carbon intensity in the electricity grid.

In the full article, Walker claims there ought to be evidence of increasing use of wind power reducing the carbon intensity of the grid - but the statistics reported show no such trend. He states that the carbon intensity has been generally steady since 1999 even though in that time wind power capacity has increased by a factor of 20. This is true, but most of that increase in wind capacity has come in the last 4-5 years and wind is still only a small part of our power supply: just 4.3% of supply in 2011[4]. You can't expect that to make much impact on carbon emissions.

He goes on to analyse in more detail the change between 2010 and 2011.  He uses figures from Digest UK Energy Statistics 2012 [4],  from which he calculates that the carbon intensity of electricity dropped 2.9% of which 'only' 1% was due to increasing wind. Actually this data is provisional for 2011. In the 2013 report carbon intensity is reduced by 3.7%. Also, Walker does not indicate how much more wind was being used: in fact the wind proportion went up from 2.7% to 4.3% i.e. 1.6%. So, 1.0% less emissions for 1.6% more wind would be a little disappointing: but DUKES reports a considerable increase in emissions from fossil fuels (3.4%) due to more coal being used instead of gas, because the gas prices went up. This means the true gains from low carbon sources were better still.

How to detect potential bias

Calculating carbon emissions from electricity generation is complicated and it is easy to mislead the unwary reader. It has taken me quite a while to follow up his references and sort out even some of the confusion in this article. One of the ways to identify likely bias is to look out for emotional wording. My suspicions were raised immediately in the first sentence of the press article by the reference to 'the wind farm juggernaut that is rampaging so relentlessly through our countryside'. Perhaps juggernaut drivers could sue for defamation of character. But doubtless these were the words of the newspaper, not Walker. The full article is less dramatic, content with '...serious alarm...erosion of democracy... quality of life ... scandal of subsidies...'.  

Wind power is particularly subject to misleading reports: see my previous posts 'Do wind farms contribute to global warming?' and 'Are wind farms merely icons of ecological faith?'.

Does use of wind power reduce carbon emissions?

Walker's paper has not answered the question to my satisfaction. I have refuted his analysis but not conclusively proven the issue either way. In fact there has been considerable debate on the subject, as excellently summarised in this post by Robin Webster in The Carbon Brief. On the pro-wind side, this references a report from National Grid to the Scottish Parliament Economy, Energy and Tourism Committee [5]. National Grid analysed generation data over three 6 month periods, 18 months in total. They looked at the amount of wind power generated, the carbon intensity of coal and gas plant that were displaced by the wind, and the amount of short term operating reserve that was used when wind power failed to live up to its promises. They concluded that the increase in carbon intensity from fossil fuel power stations offset less than 1% of the emissions savings from using wind.

This report has been criticised for assuming that wind power displaces fossil fuel use rather than nuclear power stations. This seems highly unlikely to me as the nuclear power stations we have currently were not designed for load following (see Nuclear Power Plants aren't just for Base Load). For example a briefing note from National Grid to DECC about how to accommodate rooftop solar PV power into the grid assumes 'There is 10GW of nuclear generation (or other generation that cannot be dispatched off)' [6]. So you can't turn nuclear off. Period. National Grid is worried about rooftop PV panels which can't be switched off either, though wind farms can be and frequently are (see 'Why do we pay wind farms to switch off'). Wind displaces gas or coal, not nuclear power.

[1] Renewable Energy: Avoid building wind farms on peat (2012) Nature
[2] Carbon Cost and Consequences (2008) E.ON
[3] The Costs and Impacts of Intermittency (2006) UKERC
[4] Digest UK Energy Statistics 2013 (DECC)
[5] Report to Scottish Parliament clarifying 'the impact of reduced thermal generation plant efficiency due to increasing intermittent wind generation on the overall carbon intensity of the electricity system' (late 2012)
[6] Solar PV Briefing Note (National Grid)

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