Do wind farms need fossil fuel back up?

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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.

A quote:

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.


4 thoughts on “Do wind farms need fossil fuel back up?

    Samuel said:
    June 2, 2013 at 6:43 am

    Hello Robert, small typo I think: “to make up for less than expected demand “. Shouldn’t it be “to make up for the more than expected demand” or “to make up for the less than expected production” ?

    I agree with your demonstration that overall windfarms are decreasing CO2 output for electricity production, but did you run these calculations on a country with a very low CO2 output like Switzerland (hydro+nuclear) ? I surmise that in this situation, it would not need too much windfarms to disrupt the filling gap capacity of hydro for peak demand and cause more CO2 (typically to pump back water in reserves.


      Robert Wilson said:
      June 2, 2013 at 9:13 am

      Thanks Samuel

      Corrected. I’m not really sure if wind farms would cause much difference to CO2 in Switzerland. Is the electricity used to fill pumped storage facilities not almost entirely nuclear (Swiss or imported French)? I guess if Switzerland replaced nuclear power plants with wind farms then they may quickly need to build gas plants to act as reserve, though can they avoid they by importing cheap electricity at night?


        Bob Wallace said:
        June 13, 2013 at 4:07 pm

        Nuclear plants also need reserve. They have to go down for refueling and maintenance. They go down following earthquakes, during floods, during heat waves, and can even be brought down by problems on the grid. Once a reactor is down it can take days to bring it back on line.

        And sometimes they go down permanently. We’ve seen four permanently disappear from the US grid this year.

        We have to backup all forms of generation. Nothing operates 24/365 without fail.


    Bob Wallace said:
    June 13, 2013 at 4:25 pm

    I suspect the wind/fossil fuel backup issue has been confused by some claiming that when we build a wind farm then we must build fossil fuel backup in order to use that wind.

    That’s a misunderstanding of what is happening. We’ve already built those fossil fuel plants (and some storage). Bringing wind on line lets us use fuel plants less, saving fuel costs and reducing CO2 generation. Many grids have adequate flexibility to allow as much as a 40% penetration of wind and solar without requiring any additional dispatchable generation or storage.

    It would be more accurate to say “Yes, the wind does not blow all the time nor does the Sun shine around the clock. We have to fill in with some other source when wind and sunshine aren’t producing. We can do that now and for some time into the future with storage and fossil fuel generation we already have.”


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