Wind farms will be responsible for adding £1,000 to household energy bills, the  Daily Express’s frontpage today claims.

The figure is based on a submission by campaign group the Scientific Alliance to the House of Lords Science and Technology committee. The committee is exploring different ways the UK can cut energy sector emissions while making sure the lights stay on.

But the alliance takes an outdated approach to calculating how many power stations the UK needs, leading it to come up with numbers that are significantly out of step with other experts.

Bill hike

Scientific Alliance says the government’s plans to reduce the UK’s emissions by ramping up renewables means the country will become increasingly vulnerable to power cuts. In particular, it’s concerned National Grid has underestimated the number of power plants needed to keep the lights on when the weather means wind and solar can’t produce much electricity and demand is high.

So it recommends building more fossil fuelled power plants. The total cost of building and operating renewables to hit the UK’s emissions targets and constructing extra power plants to avoid power cuts? £26 billion a year.

The Express appears to have divided that figure by the number of UK households, about 26 million, to get its headline stat – that government support for windfarms will add £1,000 a year to an average household’s electricity bill by 2030.

We asked Scientific Alliance to explain how it had calculated the figure, but it told us the researcher responsible was unavailable.

Assumptions

Nonetheless, Scientific Alliance’s submission does offer some clues as to how it came up with the number. Its estimates are based on a series of assumptions about the UK’s future energy mix. Let’s leave aside the fact that predicting the future of energy costs is notoriously difficult and take a look at those assumptions in more detail.

The alliance uses as its starting point the National Grid’s Future Energy Scenarios, which describe four possible futures for the UK’s energy mix. These are not forecasts and it isn’t possible to say which of the four is most likely.

National Grid market outlook manager Gary Dolphin says:

“We like to believe each scenario is equally plausible and that they collectively define an envelope within which the true future lies.”

The Scientific Alliance takes the slightly unusual step of calculating an average of the four scenarios. So if the total installed electricity generating capacity in one scenario is 105 gigawatts and in another it’s 93 gigawatts then the alliance average this out to 99 gigawatts.

This is a questionable approach. The scenarios each reflect different plausible future pathways depending on economic growth, energy demand, changing costs and so on. It’s not clear what taking an “average” of the scenarios actually produces.

Irrespective, the alliance then asserts that additional gas capacity is required over and above the levels in the “average” scenario it has created. It thinks this is necessary in order to ensure security of supply: to keep the lights on, if you like.

The Scientific Alliance metric for security of supply is based on calculating the buffer of total generating capacity over peak electricity demand.

To do this it makes assumptions about the availability of different generating capacity that appear unsupportable. It says nuclear, coal and gas power are available 100 per cent of the time for instance, even though government figures show this is not the case. It then assumes windfarms are available at only 9.6 per cent of installed capacity. These percentages represent the “de-rated capacity” and are supposed to account for maintenance closures or windless days.

This approach, and the specific de-rating factors it uses, discounts wind compared to traditional generating capacity. In turn this drives the alliance’s claimed requirements for additional gas supplies.

This way of calculating security of supply is now rather outdated. The way the Scientific Alliance measure the chance of blackouts has been abandoned by the National Grid, energy market regulator Ofgem, the UK government and those of France, Ireland and the Netherlands.

Michael Grubb, professor of energy policy at University College London tells Carbon Brief the de-rated capacity margin metric was rejected long ago. The government agrees. It says “We… do not expect the de-rated capacity margin to remain a good metric of security of supply”.

Why? It’s to do with how the approach treats variable power sources – like renewables. Windfarms rarely put out their average de-rated capacity. The variation between a windy day and a calm one is huge, in other words.

Put this alongside how the UK energy mix has evolved, with better interconnection to electricity grids in France and the Netherlands, and National Grid says the way demand is balanced against supply has also become much more complicated – and sophisticated.

All those factors lead Ofgem to say that the risk of blackouts remains manageable, despite the de-rated capacity approach now suggesting tighter margins for the energy system.

The government has set a new standard for reliability that reflects the way the electricity grid has changed. This explicitly tries to account for the fact that wind output is variable using a statistical approach factoring in how much wind capacity is installed and how often the wind stops blowing, over the course of a full winter.

National Grid has constrained each of its scenarios to meet this government standard. What this means is that while they vary in other ways, each of them is required to satisfy the reliability requirement to avoid the risk of blackouts.

It is these scenarios, with reliability locked in, that the Scientific Alliance uses as a starting point. Adding additional capacity to these scenarios when they are already designed to meet future demand in full, without breaching government reliability standards, seems like a strange thing to do. But this is what the alliance analysis suggests we do, and of course costs are pushed up as a result.