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Does wind power reduce carbon emissions?

Since their output is variable, wind turbines have to be backed up, usually by fossil fuel plants, so some say that the carbon savings from having wind power on the grid are undermined. This issue has been the subject of sometimes heated debated for some time.

Back in 2008, the House of Lords Select Committee on Economic Affairs report on ‘The Economics of Renewable Energy’ referred to an argument made to the Committee by a witness from the Renewable Energy Foundation (Campbell Dunford) who claimed that any carbon savings from wind power were offset by the need to run conventional (and flexible) fossil fuel plant at part load to balance the fluctuations in wind output (e.g. to balance supply and demand when the wind is blowing less). Part loading means that the backup plants are run inefficiently, so producing more CO2 per kWh of output than they otherwise would.

Based on other inputs to their review, the Committee disagreed with this argument. They concluded that ‘The need to part-load conventional plant to balance the fluctuations in wind output does not have a significant impact on the net carbon savings from wind generation’.

In its response to the Select Committee, the government agreed with this statement and estimated the net saving from raising the share of renewable electricity to 32% to be about 45-50 million tonnes of carbon dioxide— about 8-9% of total CO2 emissions—after taking account of the cost of part- loading plant.

Certainly it is usually argued that the extra cost of fuel/ and the extra CO2 produced is only of the order of 2-3%. The issue is explored in Godfrey Boyle’s ‘Renewable Energy and the Grid: The Challenge of Variability’ (Earthscan, 2007).

However, some critics point to new real time data from the USA and elsewhere, which they claim indicates otherwise: http://theenergycollective.com/willem-post/64492/wind-energy-reduces-co2-emissions-few-percent

For example, one analysis of recent US data suggests emission savings from wind plant are as low as 0.1 tons of CO2/MWh in California, compared to an average figure for the US as a whole of 0.6 and a figure of 0.8 attributed to the American Wind Energy Association. http://www.bentekenergy.com/documents/BENTEKTheWindPowerParadox071911_Sample.pdf

But it rather depends on what fuel is being displaced. In California it’s mostly (low carbon) gas and (zero carbon) hydro, whereas in the Mid West it’s mostly (high carbon) coal- so the figure there is 1ton/Mwh saved.

The carbon saving benefits from wind are also undermined in the US by the fact that, when wind availability is high, much of the potential output from wind projects has to be curtailed- i.e. not used. This is mainly due to there being weak grid links, which are unable to take it all and distribute it to where it is needed. The same thing has happened recently in Scotland. Having large inflexible ‘must run’ nuclear power plants on the grid also doesn’t help.

Better grid links can clearly help reduce the need for wind curtailment, so of course could electricity storage, which will also help when wind availability is low, although energy storage is expensive (see my earlier Blogs). Interactive load management to reduce (or shift) demand peaks can help reduce the need for back up when there is less wind available, so can imports of energy from wind generators elsewhere, where it is more windy, via a long distance supergrid, balanced by exports when wind is available and demand locally is low. See http://www.wseas.us/e-library/conferences/2010/Cambridge/EE/EE-29.pdf

So there could be solutions, and they may not add too much extra cost. Certainly the recent European Wind Integration Study, produced by the European Transmission System Operators, says the benefits of wind energy in terms of fuel and CO2 saving greatly exceed grid balancing and reinforcement costs, put at 0.21-0.26 p/kWh and 0.4p/kWh respectively, for 181 GW of wind; and extra grid reinforcement could reduce the former to 0.17p/kWh. www.wind-integration.eu/downloads/library/EWISStandaloneExecutive_Summary.pdf

And beyond that, the EWEA Tradewind study and Greenpeace’s various [R]evolution reports suggested that pan-EU supergrids could offer major benefits in terms of reducing the impact of local variability- for example perhaps doubling wind power’s capacity credit. http://www.erec.org/fileadmin/erec_docs/Documents/Publications/global%20energy%20grid%20scenario.pdf and www.trade-wind.eu

However perhaps inevitably not every one agrees. For example , Pöyry’s North European Wind and Solar Intermittency Study (NEWSIS) has found that ‘The creation of an offshore ‘super grid’ and a major upgrade of energy interconnections are not the silver bullet solutions to Europe’s energy needs’.

It says that the introduction of improved connectivity would only partially alleviate the volatility of increased renewable energy generation. Basically it claims that wind and solar output will be highly variable and will not ‘average out’, even over wide areas- it looks at the NW of Europe- and concludes that ‘heavy reinforcement of interconnection doesn’t appear to offset the need for very much backup plant’. So it claims that ‘inter-connectors are not a complete solution’. Pöyry study summary: www.poyry. com/linked/en/press/NEWSIS.pdf

Actually no one has said that inter-connectors were ‘a complete solution’- there would also be a need for backup, storage, and demand side management and so on. Moreover, unlike the earlier EWEA ‘Tradewind’ study and Greenpeace reports, which looked across the whole of Europe, Pöyry only looked at the North West. Assuming a wider footprint- including the sunny south, and the windy east, and possibly also North Africa, then the situation would be very different- as has been explored in Gregor Czich’s seminal study ‘Scenarios for a Future Electricity Supply’, now published by the IET. www.theiet.org/publishing/books/renewable/scenarios.cfm

However the debate on wind balancing continues, with some inputs being quite dramatic. For example, a study of the influence of wind energy on the CO2 output of fossil-fired generation of electricity in Ireland claims that, in absence of hydro buffer storage, the CO2 production of the conventional generators increases with wind energy penetration, and that the reduction of CO2 emissions is at most ‘a few percent’, if gas fired generation is used for balancing a 30% share of wind energy. www.clepair.net/IerlandUdo.html http://www.clepair.net/IerlandUdo.html

Even if only partly true, it looks like a good case for a supergrid link- Ireland’s grid is too small.

A recent input to the debate is a new EU “Offshore Grid” project analysis, co-financed by the European Commission, which looks at the benefits of building a meshed European grid offshore, which it says will significantly increase security of electricity supply across the EU. www.ewea.org/fileadmin/eweadocuments/documents/publications/reports/OffshoreGrid_report.pdf.

The House of Commons Select Committee on Energy and Climate Change has also recently backed the supergrid: the IET had told the Committee, a supergrid could provide a much wider range of opportunities to export excess electricity when the wind is blowing and new routes to import electricity at times of low-supply. www.publications.parliament.uk/pa/cm201012/cmselect/cmenergy/1040/104003.htm

Supergrids are not the only or complete answer to variability, but along with other measures, they should be able to help. For an extensive, authoritative, report on the variability issue see the IEA’s ‘Harnessing -Variable Renewables.’ http://www.oecdbookshop.org/oecd/display.asp?sf1=identifiers&st1=612011171P1&LANG=EN

Posted by Dave Elliott on November 20, 2011 12:10 PM | Permalink