Today’s Telegraph has a piece by Geoffrey Lean arguing that wind farms do not need fossil fuel back up for when the wind doesn’t blow.
It has become an article of popular faith that building wind farms also involves constructing fossil-fuelled power stations for back‑up when the weather is calm. As a result, some opponents go on to say, wind turbines do little or nothing to cut carbon dioxide emissions.
Now the National Grid has studied what actually happens in practice, with explosive, if surprising, results. Between April 2011 and September 2012 – its head of energy strategy, Richard Smith, told the Hay Festival – wind produced some 23,700 gigawatt hours (GWh) of power. Only 22GWh of power from fossil fuels was needed to fill the gaps when the wind didn’t blow. That’s less than a thousandth of the turbines’ output.
Unfortunately Lean has got things totally confused here. He has mixed up the need for back up capacity for when it is not windy, a real one, with the need for back up capacity for when there is less wind than expected
I have covered these issues before, so if you want a fuller explanation read this and this. To realize that Lean is mistaken about the need for back up when it’s not windy just consider the hourly average wind farm output in the UK in December 2011.
You don’t need to do a particularly extensive mathematical analysis to realise that the fossil fuels needed “to fill the gaps when the wind didn’t blow” is a great deal more than a thousandth of total turbine output. That’s rather clear.
So, what is Lean actually referring to? The 22 GWh figure he mentions is not the amount of fossil fuels needed to fill the gap, but the increase in what is called the “Short Term Operating Reserve” that was due to wind farms. This was estimated by the National Grid to be 22 GWh over a 18 month period, the figure Lean refers to. However, this has absolutely nothing to do with the wind not blowing, but to do with wind farms producing lower output than was forecast. Essentially you need to quickly fire up OCGT gas plants to make up for less than expected wind farm output (these have higher CO2 emissions than regularly gas plants, hence the “wind farms don’t reduce emissions claim”). And this can happen on windy or calm days. In fact, I believe it’s more likely to happen when it is windy, not when it’s calm. However OCGT plants are fired up too rarely too make much difference to the carbon emissions of wind farms.
So yes, carbon emissions are reduced by wind farms, but if people wish to debunk these claims they really should make sure they know what they are in the first place.