The question comes as surely as a rainy day in Scotland.

Talk – or write – about renewable energy or the climate emergency and somebody will, inevitably, make the same dull rhetorical point.

What happens, they will ask, when the wind stops blowing?

Well, right now what mostly happens is that gas or nuclear power picks up the slack.

That is about to change as Scotland pioneers what energy experts call “super batteries”.

Some people have called the rise of the battery a new “Ion Age” – a pun on the lithium ion technology which is basically the same as those we all have in our TVs and mobile phones.

ScottishPower has already announced plans for a first such bank of lithium ion electricity storage units at its giant Whitelee wind farm – and this was approved by local and national authorities last year.

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But now the chief executive of ScottishPower Renewables, Lindsay McQuade, says she intends to develop similar facilities – which she describes as the size of a supermarket – up and down the country.

The super battery revolution effectively marks a second stage in Scotland’s transition to renewable electricity.

Bluntly, McQuade said, it means we are less likely to need to turn on the gas if the wind stops blowing.

She said: “In Scotland we have some wonderful natural resource – which is code for ‘challenging weather’.

“But even here the wind does not blow all the time, the sun does not shine all the time, and even the rain does not fall all the time.”

ScottishPower executives say that batteries like this would have been science fiction as little as a decade ago.

The company does have the ability to regulate power output, largely to mitigate against the inflexibility of nuclear power plants, which run steadily day and night.

It owns and operates the giant accumulator battery of Ben Cruachan in Argyll.

Essentially, this facility pumps water up to the top of a hill during the night (when nuclear power is cheap) and then releases the same water through hydropower turbines during the day when demand is greatest.

Such stations can also be used to smooth out output of wind farms. As recently as 2017, this type of pumped hydropower accounted for 97% of the world’s “utility-scale” stored energy.

But McQuade is looking at smaller-scale, more nimble solutions, albeit on a grand scale.

She said: “These batteries are going to be located at key points on the grid, more than likely alongside existing wind generation that we have. This is so we can smooth the profile of output from those wind farms.

“We have been considering energy storage as we have been developing our fleet of onshore wind generators, the largest in the UK.

“We have over 1,100 turbines.

“We started studying storage four or five years ago and the fruits are starting to come through as we start construction of 104 megawatts of battery across the UK and Ireland.

“The largest in Scotland will be the Whitelee battery story project, which will be co-located with the wind farm.”

ScottishPower will put them next to existing or new wind farms or electricity substations. Officials say they look like “medium-sized supermarkets” and jokingly refer to German discount retailers to explain the scale of the facilities.

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McQuade said the dull exterior would conceal incredibly sophisticated kit inside. She said: “It is a simple shed. Inside we are going to have racks of batteries and some really intelligent software to help us provide not only power but a range of services to help the resilience and stability of the National Grid that would traditionally have come from coal or gas stations.”

The National Grid has traditionally used coal or gas-burning plants – or sites like Cruachan – when renewables were offline or when demand surged.

Renewables accounted for three-quarters of gross electricity output in 2018.

But they only made up 57% of consumption as Scotland exported power when, crudely, the wind was blowing. Scotland is one of Europe’s greenest generators of electricity (though the nation is overall mid-ranking on energy because of its addiction to domestic gas heating).

However, outages at its Hunterston B nuclear power plant meant that it actually burned more gas for power in 2018 than at any tine since 2011.

McQuade said consumers understood batteries. She said: “If we are sleeping at night, and the wind is blowing, we can charge up our batteries, much as you would charge up your phone at night or, increasingly, your electric vehicle.

“Peak power demand comes during the day. But as we go forward that is going to smooth out because people are going to start using electricity very differently.

“Consumers’ relationship to electricity is changing. They have an expectation that it is green and low carbon and that they are making a contribution towards net zero.

“There is little point having an electric vehicle that is powered by a battery that in turn is powered by fossil fuels.”

The cost of batteries is collapsing as orders get bigger and manufacturers start to enjoy economies of scale. Bloomberg New Energy Finance, a firm of business analysts, last year said prices had dropped 87% since the 2010.

The inventors of lithium ion batteries were last year awarded the Nobel Prize for physics and demand for their product is set to soar, not least as electric cars finally take off.

German-American John B Goodenough, Briton M Stanley Whittingham and Japan’s Akira Yoshino shared the prize after the technology was first developed during the oil crisis of the early 1970s. Their secret? Lithium ion batteries are lighter than other technologies and therefore ideal for cars and phones.

The return of relatively cheap oil meant their invention has taken decades to become a commercial reality.

Now Bloomberg is predicting demand for the technology will quintuple between now and 2025.

Much of that demand is for the kind of back-up battery power stations ScottishPower is talking about. Bloomberg NEF expects a 122-fold rise in the capacity of energy storage installations – what it calls fixed super batteries – between 2018 and 2040.

That, even with the continued falling price of batteries, means a $662 billion global investment. But solar and wind energy together with batteries, the analysts said, and their share of the global market, will rise from 7% now to 40% in 2040.

Batteries are particularly important for solar farms, which, rather unsurprisingly, generate the most electricity when the sun is highest at or around midday.

That could be a game-changer in developing countries with plentiful sunshine but not much of a power grid.

The Faraday Institution, a body bringing together battery researchers at seven English universities, has suggested the technology could revolutionise life for people who are off grids, or on weak grids. Many communities in poor countries depend on expensive and unreliable diesel generators.

A combination of cheap, clean renewable energy – backed up by increasingly cheap batteries – could bring some of the world’s 800 million people without power into the light.

The institution, which has so far focused on batteries for cars, last month announced a research project into replacing some 25 million fossil-fuel generators in the global south. That could stop 100 million tonnes of carbon getting into the atmosphere a year. But the aim is not just to stave off the climate emergency, it is to end outages costing Africans alone up to 2% of their GDP every year.

Closer to home some businesses are also looking to invest in on-site batteries to power their facilities to smooth out their power costs. A hotel in Edinburgh, a Premier Inn, last summer unveiled proposals for a 100-kilowatt battery last year. It said the new facility would save but £20,000 a year.

Late last month, an expansion to Europe’s biggest battery farm, in Wiltshire, was announced.

So how many super batteries will Scotland have? That, McQuade said, is an interesting question. She did not answer but stressed that demand for electricity was going to boom as Scotland moves to net zero by 2045. And with power exports set to boom, the country will want to make sure it does not let any turbines spin for no good reason.

There is big money in that wind.

Lighting the way ahead

Scottish mobile electricity generation giant Aggreko is spearheading efforts to get develop mobile renewable energy.

The company’s Dumbarton factory has started making portable batteries to supplement and replace traditional generators.

Aggreko specialises in providing off-grid electricity for everything from remote mines and disaster zones to music festivals and sports events, such as this summer’s (still planned) Tokyo’s Olympics.

Normally its sets up diesel generators in shipping containers. Now it is looking at providing batteries that can either be powered up by renewable energy in advance or used in conjunction with kit like solar panels or small wind turbines.

Aine Finlayson, the company’s head of manufacturing, explained: “Traditionally we would have containerized thermal engines to generate power when you don’t have access to the grid.

What you are going to find we will have some battery and some thermal.

“You can use the batteries to balance the engine, increasingly its efficiency and reducing its carbon footprint.

“But also, more and more, as we go we can connect in to wind and solar.

“So we are delivering building blocks that can can talk to each other.

“That means that when the wind stops blowing batteries can kick in and when batteries are depleted, thermal can work.”

Ms Finlayson said much of the early work abroad involved batteries and some thermal power backing up solar panels.

Aggreko has already supplied such building blocks to a mine complex in Mali, in west Africa. The power plant, at remote Syama, saves 40% off the cost of electricity and reduces carbon by 20%.

Ms Finlayson said that customers wanted to demonstrate that they were trying to reduce their carbon footprint.

Technologically, she said the main thing was that a battery had the ability to kick in instantaneously, to ensure reliability.

In poorer countries, blackouts and power frequency changes can cause serious problems for mining, manufacturing and public services.

ScottishPower is already looking to build batteries to ensure domestic supplies are maintained when the wind does not blow. International agencies such as the World Bank are eager to support power storage in developing countries with less sophisticated grids but potential supplies of green wind or solar power.

Mali, in the Sahel, has a ready supply of sunshine in the way that Scotland has wind. It is currently developing huge solar panel farms.

But it will need battery technology to make sure it can keep round-the-clock, round-the-year output.

Governments are not just looking to electrify homes - they want to develop light industry, such as food processing, and support agriculture with, for example, electric-power irrigation or well pumps.