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How many windfarms does it take to power a lightbulb?

Nigel Williams, 14 March 2013

It’s cold. On 14th March 2013, Westminster is promised a maximum of 7° C. There was frost on the ground as commuters set off to work. Obviously we look to sources of energy to provide heating and other comforts. March, month of the vernal equinox, is traditionally famous for its windiness so wind-generated electricity looks like a good, renewable place to start. Renewable UK, the trade body for wind and marine energy, inform us that 8.3 GW of wind capacity now powers the equivalent of very nearly 4.7 million homes.

small heater


Any reduction in greenhouse gas output is welcome but it is worth seeing how far that wind energy goes. The Balancing Mechanism Recording System puts a wealth of data about energy reaching the National Grid to a website. This morning, receipts from wind peaked at 765 MW. Some wind energy is used before it reaches the grid, so we may need to round up the figures. Spreading that 765 MW between 4.7 million homes rounds up to 200W each, which is enough to keep one bar of an electric heater on for twelve minutes in the hour, while switching off all other electrical items.

The difficulty lies in there being three ways of considering the output of an energy source. These are the maximum output, the average output and the dependable output. My example uses the lowest of these so may be a little contentious. Today is an unusually still day but also a cold one. Four thousand four hundred wind turbines are contributing to the grid an average of 200 kW each. If those 4.7 million homes want to keep the electric heater on continuously, they need to find and indirectly to pay for an alternative source. I have written at greater length about the costs here.

The national grid does a great service to the wind industry in filling in the gaps. Nuclear stations are at the opposite extreme, providing a constant 7½ GW whether demand is high or low. ‘The system’ adjusts for the imbalances. Interconnectors with Ireland, the Netherlands and France, pumped storage and fossil-fuel stations that can be turned up or down make the difference between the 200W each on offer on still days and what’s needed for a comfortable lifestyle. When the wind is blowing, less fossil fuel is burned and savings are possible, although there are some efficiency-losses from running power stations below their optimum workload. There is a danger in attributing all the carbon-savings to the wind turbines, since without ‘the system’ they cannot operate in a dependable manner. As an alternative to building new windfarms, investing in the system, whether through more interconnections, storage facilities, renewables with a different pattern of intermittency or flexible, gas power stations have just as much potential. They only have to provide a dependable 200 kW to beat the average unaided wind turbine.

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