According to this article: https://www.rechargenews.com/energy-transition/the-amount-of-energy-required-by-direct-air-carbon-capture-proves-it-is-an-exercise-in

According to this article: https://www.rechargenews.com/energy-transition/the-amount-of-energy-required-by-direct-air-carbon-capture-proves-it-is-an-exercise-in-futility/2-1-1067588 https://www.rechargenews.com/energy-transition/the-amount-of... The cost of carbon capture straight from the air is about 10GJ per Tonne (they quote 8.8 and 14 from competing sources). Which is about 2800 kWh That would put a serious damper on the efficiency, but might make it viable even when 'easy' sources of CO2 (like the exhaust of fossil power plants) are no longer available.