Balancing the UK's grid system to accommodate variability of wind power supplying more than 20% of all electricity should be manageable, at least until 2020, according to an analysis by the Department of Energy and Climate Change (Decc) as part of its blueprint for renewable energy strategy.
Decc drew on findings of a report by British system operator National Grid, which investigated the increased implementation of renewable energy sources for power generation. The report, Operating the Electricity Transmission Networks in 2020, is one of three reports published this summer that all but dismissed variability as an obstacle to large-scale deployment of wind.
The other reports are Poyry Consulting's Impact of Intermittency, and Managing Variability, by technology consultant David Milborrow, which was published by an environmental coalition: WWF, the Royal Society for the Protection of Birds, Greenpeace and Friends of the Earth. Milborrow is also a contributing consultant to Windpower Monthly.
National Grid's report stresses that additional backup generation is not the only means of accommodating variable generation, or the gradual rise and ebb of power. It sees new technologies providing flexibility on Britain's network: demand management, "smart meters" that relay data on power consumption to utilities for billing, energy storage devices and electric cars. Even without these, it adds, variability can be managed and the costs to consumers of increased wind generation on the system can be kept down through better wind forecasting, more sophisticated control systems and greater grid interconnection with Europe.
According to Milborrow's report, the additional variability costs for wind capacity that are needed to meet the government's 2020 targets would be around £2/MWh, adding just 2% to customers' electricity bills. Wind penetrations of up to 40% could still be managed with modest variability costs of between £3.5-7/MWh, he says. Even at the higher end, the added cost to domestic consumers would be around 6%. Milborrow adds that breakdowns of thermal plants, in particular large coal and nuclear generation, pose more of a threat to network stability than the variations in wind output.
The Poyry report, agreeing with Milborrow, says that if a new generation of larger nuclear power stations is built, more backup capacity will be needed on the system to cope with the potential sudden loss of a 1600 MW plant. Poyry's year-long study shows that the challenge to the system of large volumes of variable wind generation is far less of an issue than its effect on market economics. In a future electricity market dominated by the vagaries of the weather, thermal plants and interconnectors will be able to deal with wind's variability, it says. But the highs and lows of electricity prices will become more extreme and the commercial risk for conventional plants operating in the market will be far higher than today.
Poyry criticises the market rules for not allocating capacity payments - fees paid to plant owners per megawatt of capacity - that would reward plants that might only run during periods of high demand. "We are concerned that there is a real challenge in delivering very low load-factor plants in the British market," it says. Decc maintains that incentives will be sufficient to encourage investment in the flexible generation needed.
Looking ahead, Decc warns that variability may present greater challenges beyond 2020 as even higher volumes of wind accompany closures of old gas and coal plants that provide flexible backup. By this time, the government hopes to see increased nuclear generation which, along with renewables and "clean coal", make up its "low carbon trinity" for future energy supplies. But Milborrow warns that these capital-intensive technologies will compete with wind over the coveted "must-run" status as operators try to run plants whenever possible to recoup fixed costs. Government and regulators will need to resolve these conflicts, he says.
The National Grid believes next-generation nuclear plants in the UK will operate more flexibly than today's. Nonetheless, it expects nuclear generators to continue to operate at base load unless stronger price signals encourage them to adjust output to meet system requirements. Based on the findings of the Poyry study, Decc believes large thermal plants will not come into significant conflict with wind until there is around 40 GW of installed wind capacity. At such a point, nuclear, coal or wind would have to be curtailed when supply exceeds demand, but the government is not saying which of its favoured technologies will enjoy must-run status.