Direct air capture's hidden energy cost

Carbon removal will likely play some role in reaching net zero. But doing so will require huge amounts of energy. It takes around 1,200 kilowatt-hours to remove a ton of carbon from the sky using direct air capture. That could be a barrier to widespread use, according to MIT Energy Initiative’s senior research engineer Howard Herzog.

The carbon removal industry expects to scale to capture billions of tons per year. That could put it in direct competition with renewable needs for other purposes like, say, keeping the lights on. (For reference, the average American home uses a little less than 900 kilowatt-hours of energy per month.) Capturing “just” 1 billion tons would essentially require all of the carbon-free energy that’s available today, including nuclear.

The high energy use also hides carbon removal’s true cost, according to Herzog, who did the energy use analysis and is skeptical the industry can reach its target price point of $100 per ton.

• Even the lowest-carbon fossil fuel, natural gas, generates almost half a ton of carbon dioxide for every ton that is taken out of the atmosphere via DAC, according to his estimates.
• In that scenario, if a DAC company says it can perform the capture for $100 per ton, that’s really the gross capture cost. The net cost is actually double that amount.
• What that means is that, for DAC to be economically feasible, the energy powering it has to be carbon-free. (Which also makes sense, because if you’re trying to pull carbon dioxide out of the air, it kind of defeats the purpose if you’re adding carbon dioxide to the atmosphere in the process.)

DAC’s high energy use points to the value of decarbonizing everything as fast as possible. One ton of carbon that doesn’t make it into the atmosphere today is one less to remove tomorrow. And that means less conflict over future renewable energy.

A version of this story appeared in Protocol’s Climate newsletter. Sign up here to get it in your inbox twice a week.