I’ve just come across a report by energy consultant Duncan Seddon in the Australasian Power Technologies publication. The title is “Do wind farms/gas turbines save carbon?”. (Of course he means “CO2 emissions”, not carbon – but I’m delighted to see the explicit link of turbines plus back-up).
The answer to the question, in brief, is “on average, no”.
For some time now I’ve been familiar with (and have repeatedly quoted) the paper by Professor Gordon Hughes of Edinburgh University “Why is wind power so expensive”, which makes the point that the very intermittency of wind means intermittent operation of the gas back-up, which means that you burn more gas, and emit more CO2, per MWh, than you would if you ran the plant properly.
I’ve tended to use formulations like “intermittent wind farms export inefficiency to the associated fossil fuel back-up, so that the emissions savings you hoped to achieve from the wind turbines are largely off-set by inefficiencies in the gas-fired power station”. So far so good, but how largely is largely?
The Seddon paper sets it out. He looks at a large number of (on-shore) wind farms across Australia, and presents voluminous figures for output and efficiency. He finds that the relative output (actual annual output as a percentage of rated capacity) varies from 22 to 42%, with an average of 33%. He also finds that where the relative output is less than 32% (that is, give or take a percentage point, about the average) there are no net savings of emissions.
This is a stunning result. The wind industry likes to pretend that every MWh generated by wind turbines represents emissions saved at a fossil fuel plant. This report shows that’s just not the case. What we’re seeing is that on above-average output, there are some emissions savings, though nothing like at the level claimed by the industry. And below average output, the turbines are actually achieving negative savings – in other words, increasing emissions.
It’s a very reasonable inference that on average across the fleet, the CO2 emissions savings achieved by wind turbines are close to zero. And since emissions are a surrogate measure of gas consumption, it follows that the net electricity production of the wind farms is also close to zero. We would do better just to build combined cycle gas, and forget about the wind turbines. This would also save the UK tens of billions of pounds.
It could be even worse than this. In another statistical study, this time for the Renewable Energy Foundation, Professor Gordon Hughes shows that across different countries and for both on-shore and off-shore turbines, the output declines by as much as half over ten to fifteen years. Seddon’s 33% average looks very like early-years performance of wind farms. Give them a few more years so that output declines, and they will all be in Seddon’s “no emissions savings” range.