Taking carbon dioxide back out of the open air is one of the hardest jobs in climate engineering, for a simple reason: there is precious little of it to catch. Whichever way you build the machine, it must swallow great volumes of sky and pay for the privilege in power. The power bill, more than anything else, is what has kept direct air capture a boutique enterprise while the gas goes on accumulating.
A research team now says it can cut that bill roughly in half. Writing in Nature Energy, they describe a device built like a battery: nine cells stacked together, each with an area of about half a letter-sized sheet of paper. A blower pushes air through winding channels cut into the plates that sandwich the cells, using parts borrowed from fuel cells. The cell itself is a nickel hydroxide design that, as it runs, exchanges the gas across a membrane — the battery does double duty as the pump.
The measured result, according to Ars Technica’s account of the paper, is electricity use of about 0.8 megawatt-hours per ton of captured CO2. Today’s facilities that strip carbon from ambient air consume in the neighbourhood of 1.5 to 3 megawatt-hours per ton. Halving energy demand would not make the technology cheap, but it would attack the single largest reason it is dear.
The arithmetic of ambition
Here a note of caution belongs in plain print. Several of the researchers belong to a startup called RepAir Carbon, which is founded on this very technology. Part of the paper is given over to sketching whether the process could make money at scale, and the people sketching it stand to benefit if the answer is yes. That does not make the numbers wrong. It does mean they should be read as a prospectus as well as a proof.
The team puts the cost of an initial small pilot plant at about $566 per ton of captured CO2. From there they borrow the learning rate of the lithium-ion battery industry — the rate at which costs have fallen as production grew — and apply standard scaling rules for larger plants. Carried forward a couple of pilot generations, that arithmetic lands at an estimated $92 per ton for a plant a thousand times the capacity of the pilot.
For comparison, Climeworks, the best-known firm in the business, is aiming to get down to $250–$350 per ton by 2030, and even that has meant learning in public how hard optimistic scaling projections are to meet. The gap between a curve on paper and a plant in a field is where most carbon-capture forecasts have gone to die.
The figure of $100 per ton has been the industry’s target for years, on the reasonable argument that costs that low could bring far wider use. More than one technology is now chasing that mark, and each new entrant improves the odds that one of them gets there. What the nine-cell stack has shown, so far, is not that it will reach $92 — nothing has shown that — but that the electricity needed to catch a ton of air’s carbon can be cut, in a working machine, by half. The projections about money are ambitions. The meter reading is a fact.