What is Direct Air Capture? (part 1)

Is it “air capture,” “air carbon capture” or “direct air capture?”

So what does it cost?

Costs are obviously important. DAC aims to enable the first end of a process for a backstop for balancing the carbon budget. Among those working on it, many consider it a technological fix with theoretically limitless scale to set the marginal cost of carbon remediation. Assuming the world decides to pay for balancing the amount of atmospheric CO2 in the atmosphere, if the cost of DACCS is less than the social cost of carbon, that is, the damage that caused by an excess ton of CO2 to the atmosphere, then this technology could become a safety net in the global drawdown. On the other hand, if DAC provides a cost effective way to extract CO2 from air to create carbon neutral liquid fuels (one of the reasons why Audi has partnered with Climeworks), then DAC is an enabler to technologies to create fossil free hydrocarbons. This could allow internal combustion engines to remain in use in a carbon constrained world while also permitting difficult to electrify (i.e. ships and airplanes) modes of transportation to run fossil free.

  • Different uses of CO2 have varied requirements. Take greenhouses, for example. Increasing the concentrations of CO2 in a greenhouse from ambient (400 parts per million (ppm)) to enriched levels (1200 ppm) has shown to increase production rates up to 40%. This is why greenhouse operators are willing to pay up to $200/ton. Plants grow through photosynthesis with light and carbon dioxide. No light, no photosynthesis. This means that either there is a required storage buffer or down time when a plant is not running. Because applications require different purity of CO2 and quantities the way in which the capital cost is calculated for a plant can be different for each instance.
  • Different applications to extract CO2 from air require preconditions for a particular process to work best. For instance, Climeworks requires heat to drive their process and is able to get it for free at their first commercial demonstration by co-locating next to an industrial plant which is shedding it. Lackner’s inventions require warm, dry, air. (More on this in a future series).
  • Storing CO2 in different formations will incur different costs. If injected underground for instance, there will be additional costs in monitoring, verification, and assessment (MVA) that this carbon is still there. The costs of injecting CO2 underground will without a doubt incur expenses for convincing the NUMBY (not under my backyard) crowd this effort is worth doing. By storing CO2 in permanent carbonate form in remote locations, MVA and NUMBY costs are virtually nil.
  • Many within the carbon capture at centralized emissions community, and certainly from within the APS report, have used arguments of the Sherwood plot to claim that DAC will never be cost competitive with CCS. The Sherwood plot claims that costs tend to scale linearly with the dilution. In other words, because carbon dioxide in the atmosphere is at 410 PPM, versus what comes out from a coal fired power plant around to 12,000 PPM, you have to work 300 times harder to catch the same amount of carbon. However, those in the field have data to suggest that costs of capture scale logarithmicly rater than linearly. This is because 1) DAC doesn’t need to capture all the carbon whereas fossil emissions do 2) methods to take advantage of passive capture or applying other available energy sources like passive evaporation 3) A Lacknerian back of the envelope: the heat combustion of gasoline for 10,000 joules results in a cubic meter of carbon dioxide in the air. If you were to think about a similar cubic meter of air for its kinetic energy density for wind power, assuming 6 m/s, it is around 20 joules. Therefore the challenge to remove a cubic meter of carbon dioxide emissions from gasoline to match the energy produced from wind requires 500 times less work to the air.
  • Cost curves look different for devices that are modular with a lower capital expenditure versus large industrial plants. One of the reasons why solar has dropped over 100 times since it was invented is because it is able to be mass produced and is modular. This continual improvement of a device allows for a quicker cost reduction than an industrial plant which is built and sees few improvements over its 30 or 40 year lifespan. Unlike a large centralized power plant, which cost upwards of a billion dollars, DAC units only require a couple million to get going.

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