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

sd.commission.org.uk

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

3 Wind power technology and network integrationAs well as coping with steep demand changesthe electricity system must also be able to dealwith sudden losses of supply. This could be afault at a large power station or the loss of amajor transmission line. The system is thereforedesigned to withstand the loss of the largestoperational unit, which currently equals 1,320MW of capacity (Sizewell B nuclear powerplant).Quality of supplyThe electricity system has an inherent level ofinertia that is represented through changes infrequency, which is allowed to deviate from thetarget of 50 Hz by a small margin of 1%.Fluctuations in frequency are a direct measure ofthe balance between demand and generation inan AC power system and in order to maintain astable frequency, and therefore quality ofsupply, the system operator contracts for anumber of balancing services.In the time horizon of less than a minute,frequency is controlled automatically throughfrequency response services, which arecontracted by the system operator. Frequencyresponse is primarily provided by large, centralgenerators (>100 MW) equipped withappropriate governing systems thatautomatically change active power output inresponse to a change in system frequency.industrial customers. If system frequency is toolow (ie. there is a shortage of generation tomeet demand), the operator can call uponallotted reserves, such as conventional plantrunning at reduced capacity (often called‘spinning reserve’ vi ) and storage facilities, suchas the two pumped storage plants in Wales vii .Load reduction, also a form of reserve, isachieved through demand management. Thisservice is provided by some large industrialcustomers, who are able to respond to a requestto reduce their demand, for which they receivea payment.In summary, the system operator needs tomanage both predictable variations in demand(such as managing morning load pickup) butalso deal with unpredictable events such asoutages of generators and errors in demandforecasts. Such losses of supply can amount toover 1,000 MW in less than a few seconds, butthe system is capable of dealing with thisthrough the use of balancing services, asdescribed above.In addition, reserve is required for themanagement of system frequency after asudden and sustained loss of generation orincrease in demand, and is provided by bothgenerating plant and load reductions from someviviiSpinning reserve is the term used to describe conventional plant which is purposely operated at lower than maximumoutput in order to provide a quick increase in output at the request of the system operator. Plant operated as spinningreserve is less efficient than when at maximum output, and the generator will usually receive a payment for this service.Pumped storage plants use cheap electricity in off-peak periods to pump water from a lower to a higher reservoir. Theycan then be called upon during peak periods to release this water back down, providing response output in around 10seconds. They are a relatively efficient way to provide rapid reserve response.sustainable development commissionWind Power in the UK 21

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