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UK: Wave, wind, sun and tide a powerful mix

For years, nuclear power has looked expensive, dangerous and dirty. That opinion may be about to change. Britain is facing a power gap of up to 2,000 megawatts (MW) of generating capacity — almost 40% of peak national demand — by 2020 as ageing, unreliable and inefficient nuclear and coal-fired power stations are shut. There is a growing consensus that only new nuclear power can plug that gap without contributing to global warming.

Renewable electricity technologies that harness wind, wave, tide and sun are all very well, the thinking goes, but their output is too variable and unpredictable to provide more than a small part of our electricity needs. Meeting the government's target of 20% renewables by 2020 could mean getting as much as 15% from wind and other intermittent sources, with the balance coming from "firm" renewables such as biomass and landfill gas. And that, say critics of renewables, is as much intermittency as the system can take. Any more and we will need huge reserves of expensive, polluting backup capacity, ready to cut in whenever the wind stops blowing.

Convinced? Think again. Research at Oxford University shows that intermittent renewables, combined with domestic combined heat and power (dCHP) could dependably provide the bulk of Britain's electricity. "By mixing between sites and mixing technologies, you can markedly reduce the variability of electricity supplied by renewables," says Graham Sinden, of Oxford's Environmental Change Institute. "And if you plan the right mix, renewable and intermittent technologies can even be made to match real-time electricity demand patterns. This reduces the need for backup, and makes renewables a serious alternative to conventional power sources." In particular, it puts renewables ahead of nuclear power, which runs at the same rate all the time regardless of fluctuations in demand.

Sinden initially looked at just three generation technologies: wind, solar and dCHP — in effect, hi-tech domestic boilers, which produce electricity as they heat water. He ran computer models of power output based on weather records going back up to 35 years, and found that electricity production could be optimised by creating a mixture of 65% wind, 25% dCHP, and 10% solar cells. The high proportion of wind is because the wind blows hardest in the winter, and in the evening — when demand is highest. The dCHP also produces more at peak times, when demand for hot water and heating is also strongest. Solar makes a smaller contribution, and produces nothing at night. But it is still important to have it in the mix as it kicks in when wind and dCHP production is lowest.

It is also essential to disperse the generators, whether wind turbines or rooftop solar cells, as widely as possible. By increasing the separation between sites, you can be sure that power is always being generated somewhere and so smooth out the supply curve. This goes against current practice, which is to put wind turbines where the wind is strongest.

Sinden's approach is remarkably effective in reducing the need for standby capacity. If offshore wind power alone were to provide an average 3,500MW of electricity — 10% of electricity demand in England and Wales — it would need to be backed up by an extra standby generating capacity of 3,135MW — 90% of average production. But using Sinden's proposed mix of technologies, only 400MW of new standby capacity would be needed — just 11%.

In his latest work, commissioned by the Carbon Trust, Sinden has been researching the roles for wave and tidal power. Wave power output is concentrated into autumn and winter, when demand is greatest: 75% of wave power is produced between October and March. Tidal power output is predictable, but variable: at any site it drops to zero four times a day on the turn of the tide; and output is three or four times greater on the spring tide than on the neap tide. "A marine-based renewable system works best when it includes both tide and wave," says Sinden. "The combination has lower variability, is better at meeting demand patterns, and makes better use of expensive transmission infrastructure."

Putting these figures together with estimates of Britain's available renewable resources, wind (onshore and offshore) could realistically provide some 35% of the UK's electricity, marine and dCHP each 10-15%, and solar cells 5-10%. In other words, more than half the UK's electricity could ultimately derive from intermittent renewables.

"In the next year or so, the UK is going to have to decide how to meet its electricity needs for the next half-century," says Sinden. "It's an incredible opportunity for renewables but my fear is that it may be missed."

Editorial Notes: More on Dr Sindens work can be seen here and here.

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