June 11, 2013 10:51 pm

UK warms to cryogenic energy stores

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Without an efficient way of storing the electricity generated by wind turbines at night, or solar panels by day, such energy could be wasted

Imagine getting up in the middle of a winter night to start the dishwasher, or staying indoors on a rare sunny day to vacuum-clean the house.

Nobody would voluntarily do this – but, for generators of renewable energy, it is a big problem. Without an efficient way of storing the electricity generated by wind turbines at night, or solar panels by day, this energy can be wasted.

Consumer habits are just not flexible enough to make use of unpredictable supplies of power from wind and solar farms.

“When we’re watching TV tonight, we should be using wind energy we produced last night,” argues professor Richard Williams, head of the College of Engineering at the University of Birmingham. “Instead, the taxpayer is paying tens of millions a year to dump it.”

According to researchers from Imperial College London, if this electricity could be efficiently stored for use later, the UK energy industry could save £10bn a year by 2050.

It is not surprising, then, that the UK government is encouraging companies to address this challenge. A competition has been organised by the Department of Energy and Climate Change (DECC), offering £17m in support funding to be split among small engineering companies that can develop electricity storage systems.

In phase one of the contest, 12 ideas have been submitted, including entries from Aston University in collaboration with Renault UK, and the Bill Gates backed US company, Energy Cache.

One of the more innovative entries has come from the private company Highview Power Storage in London. At its 350KW pilot plant in Slough, Berkshire, electricity is used to cool air to its liquid state at minus 196C, which is stored in insulated containers. When power is needed, this liquid air can be warmed and converted back to gas to drive electricity generating turbines. Each litre of liquid air expands to 700 litres of gas. With further work done to improve efficiency, Highview be­lieves its “cryogenic” storage system could provide a cheap means of smoothing wind energy supply.

At present, UK electricity supply can only be regulated by turning generating plants off and on – and compensating them. Last year, wind energy companies received £34m of “constraint payments” from National Grid to keep their blades idle during periods of localised excess supply. Fossil-fuel power stations are also fired up and down in line with demand, and get constraint payments.

When we’re watching TV tonight, we should be using wind energy we produced last night. Instead, the taxpayer is paying tens of millions a year to dump it

- Professor Richard Williams

Balancing supply on the grid is likely to become even more difficult as the proportion of electricity generated from renewable sources increases from just 11 per cent at present to a targeted 30 per cent by 2020, and old coal and nuclear plants are closed.

Part of the broader solution is better grid interconnection, allowing electricity to flow from surplus to shortage areas, but the DECC also expects storage to play a bigger role in a renewable energy intensive future.

Some storage technologies are already in use. Pump-storage hydroelectric dams, such as Dinorwig, in North Wales, have been used for decades. Excess electricity is used to pump water up a mountainside, where it is stored in a reservoir and released through hydroelectric dams when there is a deficit. Suitable sites are limited. Large batteries are another option, but they use expensive rare-earth elements.

“Liquid air storage is really interesting in that it’s one of the greener storage technologies,” says Mike Wilks at Pöyry, a specialist energy consultancy.

“If you look at embedded carbon costs, batteries aren’t that green.”

Liquid air systems have the potential to provide new employment opportunities, as well. A study by academics from the Centre for Low Carbon Futures suggests liquid air energy storage could create 20,000 UK jobs, with up to 60 per cent of the value of the installations originating from British manufacturers.

“I wanted it to be built out of existing supply chains rather than novel components,” says Toby Peters, Highview founder and chief operating officer. “What we wanted to do was walk quite slowly with rigorous testing and academic evaluation at each stage, as the idea of using liquid air is a bit left field.”

Leftfield, perhaps, but it has won important backers. National Grid and the construction company Costain have joined Highview as partners in building a larger demonstration plant at the Isle of Grain liquefied natural gas terminal. Here, excess cold from the gas facilities can be used to speed liquefaction, and waste heat from a nearby power station to up the gas expansion.

When up and running, the demonstrator will aim to generate 6MW of power for up to five hours – enough to supply a town with 10,000 houses during peak demand, Highview says. It is hoping that the plant will operate commercially from 2015.

Compared with their US competitors, though, UK companies appear some way behind in storage technology. A £17m funding pot from DECC is also meagre when compared with the more than £1bn available for carbon capture systems.

Nonetheless, professor Williams is optimistic that a nation worried about keeping the lights on will see the attractions of cryogenic innovation. “Many nations have invested billions in sophisticated battery and fuel cell technology, and this represents a radical shift in approach,” he says.

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