Petrol from air revisited: The energy storage debate

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It sounded too good to be true and two weeks later, debate rages on about the "petrol from air" idea - but it has opened the lid on a wider and arguably more crucial debate: how to efficiently store energy when it is in surplus.

A front-page story in the UK's Independent newspaper profiled a small firm in north-east England called Air Fuel Synthesis, who aimed to suck carbon dioxide and water from the air and convert it through various chemical means back into gasoline.

The story spread like wildfire, particularly among groups concerned with green technology.

The firm said it was seeking funding to scale up its operations; its principal investor later told the Independent that calls flooded in (although approaches from petroleum industry offers made him "shudder"). Meanwhile, Investing Daily advised potential partners unequivocally to beware.

But as BBC News and others noted, the chemical processes behind the idea are not new; the real question is whether combining them to make petrol is sensible in economic and energy-efficiency terms.

Battery of ideas

"I think it was beautifully presented from a media impact point of view, but the reality is that it's one of a vast family of chemical processing techniques," said John Loughhead, executive director of the UK Energy Research Centre.

"It's one branch of the energy storage movement but it probably is, I would say, in the slightly less interesting branch of energy storage."

Global debates about CO2 reduction and the coming end of fossil fuel resources have been joined often by more national and local debates about renewable energy resources.

Start Quote

I don't know of anybody who's sat down and looked at the potential range [of energy storage ideas] and tried to assess their practicality and sustainability”

End Quote Malcolm Wilkinson Institution of Chemical Engineers

But what seems to be debated least is how to manage the energy that will come from them.

The fickle nature of nature means that neither wind nor solar power can be expected to produce energy in the quantities and at the times we need. Nuclear power is more an on-or-off proposition than an up-and-down one.

Ideas to store this "wrong-time" energy abound.

Among the more efficient is simply pumping water uphill when consumer demand is low, and using it to drive turbines when demand picks up. Here, the question might be one of whether there are enough hills around.

A good old-fashioned battery is about as efficient, but for wide-scale adoption a great many batteries would be needed, each requiring non-renewable materials.

The idea of compressing air in vast quantities in underground caverns, or even liquefying it, have been mooted. The release of the air could drive turbines directly or help to triple the power output of gas-fired power stations.

Then there is the idea of modifying the energy infrastructure we already have. Current electric cars are effectively batteries on wheels, and could plug in to serve as stores for wrong-time electricity.

And the "smart loads" idea envisions, for example, a refrigerator that can sense when electricity demand is high and switch off accordingly.

Prof Loughhead said that just such a scheme has been in place for decades in New Zealand, where hot-water heaters are controlled centrally by the electricity grid in a bid to actively manage loads - what has in modern circles been called the "smart grid" approach.

Old-fashioned electricity meters All this could be replaced with meters that bring in and send out energy

"With none of the technologies we have today, they were able to do something fairly sophisticated," he said.

"However complicated it sounds because we've not yet done it, the odds are we would be able to do it if we chose to."

And then there are the schemes that store energy directly in chemical bonds, like splitting water to sequester hydrogen, or making more familiar fuels such as petrol.

Malcolm Wilkinson, chair of the Institution of Chemical Engineers' sustainability group, told BBC News that while the petrol-from-air idea has brought energy storage to a wider audience, it could hamper wider efforts "if it starts to attract an unreasonable sort of funding to pursue it".

"I don't know of anybody who's sat down and looked at the potential range [of energy storage ideas] and tried to assess their practicality and sustainability in terms of the total life cycle of the technology," he said.

"You have to make a judgement at a fairly early stage of technology development and decide which are going to have a better chance of being successful, and this is not one that I think you'd put close to top of the pile."

For its part, Air Fuel Synthesis told BBC News in October that its near-term goal was to provide high-purity fuels to the relatively small-scale motorsport industry, but the firm's website adds that "we will become increasingly relevant to wider fuel markets as long-term fossil-oil prices rise inexorably and inevitably."

For Richard Darton, co-director of Oxford University's Geoengineering Programme, the issue is that such schemes detract from the wider issues that already dominate the energy and climate debates.

"We could make petrol from water and carbon dioxide captured from the air, but it will not help solve our energy problems - quite the reverse," he told BBC News.

"We should be focussing our efforts on improving our energy efficiency, and also reducing our consumption of fossil fuels. These are the really urgent priorities."

John Loughhead and Malcolm Wilkinson spoke to the Material World programme on Radio 4, which will be re-broadcast at 21:00 on Monday 5 November, and will be available on iPlayer.

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