Paying the wind not to blow? It sounds crazy. The Scottish Sunday Timesreportswindfarms were paid £35m for “wasted energy” in the financial year 2013/14.

But the payments are probably cheaper than alternative strategies and are only a small fraction of the money spent on balancing the grid.

The newspaper writes:

“About £35m has been awarded since the start of the financial year to the owners of 21 renewables projects – all of them in Scotland – because Britain’s power network could not cope with the energy they produced.”

Breaktime brew

The national grid is responsible for balancing supply and demand on the electricity network. At its simplest this involves anticipating the power surge when millions of kettles are switched on around the same time during breaks in popular TV shows likeCoronation Streetor England’sWorld Cuphalf times.

The grid has to deal with the unexpected shutdowns that can occur when coal, gas ornuclearpower stations go offline due to faults. Electricity output from windfarms varies too, as some days are windier than others, though forecasts are pretty accurate up to a day in advance.

Sometimes operators are paid to scale back or evenstopproducing power in order to help balance these factors out. Gas operators can be paid to fire up at short notice too. These are both called “constraint payments”.

Over the past four full financial years windfarm operators have received £92 million of these payments, an officialreporton the subject shows.

The amount varies from year to year depending on the status of grid connections to new windfarms, upgrade work to strengthen the grid, maintenance after storms, changing demand and a host of other factors. Last financial year the cost was £50 million. This is actually more than the Sunday Times reported.

In the financial year 2014/15 the figure reached £11.6 million by the end of September, as the chart below shows.

Source: National GridMonthly Balancing Services Summary reports

The net cost added to consumer energy bills would have around a third of that amount, however. When windfarm operators accept money from National Grid to switch off they must forego the renewable energy subsidies they would have earned otherwise.

Operators received about £85 for each megawatt hour of electricity not produced in 2013/14 but would have earned £56 insubsidies. The cost of paying windfarms not to produce a unit of electricity has fallen by one third since 2012, according tofiguresfrom anti-windfarm group the Renewable Energy Foundation (REF).

Windfarm operators are not the only ones to get constraint payments, however. In the 2013/14 financial year, gas operators received much more money. They netted £254m, three-quarters of the total £340m paid out by National Grid to balance the network.

Source: National GridMonthly Balancing Services Summary 2013/14

Constraint payments are preferable to over-engineering the grid with excess capacity that will hardly ever be used, a spokesman for National Grid says. “You would not build a motorway to deal with a once-a-year traffic jam,” he argues.

Grid upgrades to accommodate new renewable electricity capacity are not always finished until after windfarms come online. But if the UK is to meet itsambitious减排目标需要的能力stalled as soon as possible.

So paying gas and wind firms to switch on – or off – to keep the grid in balance is probably a necessary evil.

Update – 17.45: we have a more detailed explanation of the increase in wind constraint payments in 2013/14 from National Grid. There are two main reasons, it says.

Firstly, more windfarms were connected in locations where enabling works were still being completed on the network. Secondly on-going work to upgrade the network in constrained areas increased grid capacity problems in the short term. The work will improve things long term.