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Eliminating carbon dioxide emissions from global energy and industrial processes is a huge undertaking. Delays abound. Renewable energy deployment needs to speed up. Electricity grids are bottlenecked. Electric vehicle sales growth has slowed. And home heat pumps are barely out of the starting gates.
Transition troubles — as well as the fact that some emissions will be very difficult to eliminate completely — are driving interest in direct air capture (DAC), a nascent technology that sucks CO₂ straight out of the air and stores it underground.
How does it work?
In outline, DAC is a simple enough proposition, requiring only modular units containing a fan and a filter. The fan draws air in and through the filter, which captures the CO₂ molecules. The filter is a solid material or a chemical solution that binds to the CO₂ and, once it can absorb no more, can be heated to release the gas.
Today, much of the resulting CO₂ is used directly — for example, to make fizzy drinks. When volumes increase, the CO₂ is expected to be transported to permanent storage sites, such as depleted gasfields.
What are the pros and cons?
The attraction of DAC is that it can be rolled out where conditions are most favourable, does not need vast areas of land, and does not require retrofitting factories or reconfiguring industrial processes. It may also be one of the small number of ways to offset emissions that cannot be avoided.
However, the key drawback is that it is currently extremely expensive. The cost of capturing carbon directly from the air and then storing it hovers at about $1,000 per tonne of CO₂. To put that in context, a permit to emit CO₂ in Europe costs well below $100 per tonne. In part, that reflects the nascent supply chain for fans and filters, which makes the kit expensive. DAC also needs a lot of energy because the concentration of CO₂ in the air is much lower than in the exhaust gas of an industrial facility.
Will it save the planet?
DAC’s future role will depend on what happens to its costs. There are hopes that these might come down significantly as the technology becomes more widely used. The capital cost of fans and filters, for instance, accounts for $330 per tonne of CO₂ captured, or about a third of the total. A fully scaled supply chain could lead to prices falling to a fraction of that. Cheaper electricity, as renewables become more abundant, should also help. Indeed, there are hopes that DAC may end up costing $100-150 per tonne of CO₂ — at the high end of, rather than off, the cost curve.
That makes DAC a contender to abate a big chunk of CO₂ emissions. The Intergovernmental Panel for Climate Change, the UN’s climate science body, posits that, to limit global warming to 1.5C above pre-industrial levels, we will need to remove between 100bn and 1,000bn tonnes of CO₂ from the atmosphere this century. At present, the world emits about 37bn tonnes a year.
Has it arrived yet?
DAC is a nascent technology but it is operational and developing. The largest plant in the world today will capture 36,000 tonnes of CO₂ per year — roughly the amount emitted by 4,500 UK households. It was inaugurated by Swiss start-up Climeworks in Iceland in May. According to the International Energy Agency, there are 130 DAC projects in the pipeline today, at various stages of development, including the concept stage.
Who are the winners and losers?
While DAC will never be competitive with, say, substituting fossil fuels with renewables in much of the power system, at the margin it may become cheaper than some of the more complex decarbonisation options.
Take the example of green aviation fuel. It is made by combining ‘green’ hydrogen — separated from the oxygen in water using renewable electricity — with CO₂ captured from biomass or directly from the air. However, such “e-fuels” may end up costing twice as much as DAC, on current estimates.
In addition, DAC’s reliance on clean electricity to power the necessary fans and heat the filters means that countries with ample sunlight, wind or — in the case of Iceland — geothermal energy, will tend to attract investment in the technology.
Who is investing in it?
One notable investor is 1PointFive, a subsidiary of US oil company Occidental, which has announced a 500,000-tonnes-per-year DAC plant. It expects this to be operational in mid-2025.
Earlier this month, Occidental agreed a deal with tech group Microsoft worth several hundred million dollars to provide 500,000 carbon credits over six years.
