Wind Power in the UK (PDF). - Sustainable Development Commission

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Wind Power in the UK (PDF). - Sustainable Development Commission

3 Wind power technology and network integrationUK may have a capacity factor of 20-40%. Theexact figure is dependent on location, technology,size, turbine reliability, and the wind conditionsduring the period of measurement – the capacityfactor during the winter is therefore much higherthan in the summer. Capacity factors are likely tobe higher in the UK than in continental Europedue to our greater wind resources.There is some disagreement over projectedaverage capacity factors for UK wind farms. Afigure of 30-35% is commonly used, but this hasbeen challenged based on the poor performanceduring 2002 (24.1%) and a number of otheryears, when wind conditions were lower thanaverage and quoted capacity factors wereparticularly low 15 .This report explicitly uses the higher figure of35% in its cost calculations, in line with theassumptions taken by Dale et al 17 in theirestimate of the ‘system cost’ of wind power, seeChapter 4. As their calculations (and a numberof others in this report) are based onassumptions for 2020, a higher capacity factor isjustifiable because capacity factors are expectedto rise over time due to the exploitation ofwindier sites (in Scotland and Northern Irelandespecially), increased offshore development(where wind conditions are more stable –capacity factors of 40% are expected 13 ), andimproved technology and reliability. A lowercapacity factor of 30% is used in Chapter 2 ofthis report as this figure relates to 2010, bywhen less of an improvement can be expected.Design lifeThe average design life of a wind turbine is about20 years. After this time, the turbine site could berefitted using the latest technology (often termedas ‘repowered’) or decommissioned; the latter issometimes a requirement of a planning decisionand a new planning application would berequired for refitting to occur. Howeverrepowering is a very practical and economicoption and has already been done in the UK.3.2 Energy balanceAlthough wind turbines do not producegreenhouse gas emissions when generatingelectricity, they are responsible for some‘embodied’ emissions resulting from the energyused in their manufacture. This is because thecurrent energy mix is primarily fossil fuel based.All electricity generating technologies, includingrenewables, will require energy duringmanufacture, construction and operation, so theenergy balance issue does not apply just towind power.However, the energy balance, or ‘payback’, ofwind power is often mentioned as a factor thatlimits its effectiveness. There are a number ofstudies on this subject, although because of thewide variations in assumptions that can be used,care should be taken when comparing differentstudies. Most studies suggest that wind turbinestake between 3 to 10 months to produce theelectricity consumed during their life-cycle -from production and installation through tomaintenance, and finally decommissioning 18 . TheHouse of Lords Science & Technology SelectCommittee reported a figure of just over oneyear for onshore wind 22 . A more recent study bythe wind turbine manufacturer, Vestas,calculates life-cycle energy values for twooperational wind farms in Denmark (onshoreand offshore) using modern 2 MW machines 19 .The results put energy payback at just undereight months for onshore turbines, and ninemonths for offshore machines. The difference isdue to the greater amount of constructionmaterials (steel and concrete) needed offshoreand the need for more extensive gridconnections. If anything, these figures are likelyto be lower in the UK due to superior windresources over Denmark, leading to moreenergy production and a quicker payback period.18 Wind Power in the UK sustainable development commission

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