Direct Air Capture

Direct Air Capture

Carbon removal potential: 0.5-5 Gt CO₂ /year¹

There’s no surer way to remove CO₂ from the atmosphere than extracting from the air and storing it away. However that certainty and permanence also comes at a price - Direct Air Capture with Carbon Storage (DAC or DACCS) is the most energy hungry, capital intensive and resource consuming of all major Carbon Removal pathways, and usually the most expensive in $ per ton terms. We are convinced DAC plays an important part in meeting our Carbon Removal goals, but also committed to taking care in placing responsible bets in this space.

Approaches to DAC vary widely, but in all cases CO₂ at atmospheric concentrations is first captured by a CO₂ loving material. Adsorption mediums include ground minerals, solid sorbents with large surface areas, liquid solvents and electrochemistry - sometimes requiring air-moving to speed up the air contacting process. Next, pure CO₂ is released though an equally wide range of desorption approaches including swings in temperature, electrical charge, pressure and/or moisture.

DAC is inherently energy hungry. The same properties that selectively bind very dilute CO₂ to sorbent materials make them reluctant to give it up without a lot of persuasion - and therefore energy. The result is that established DAC practices typically require in excess of 2,000 kWh per ton of CO₂ captured. In some cases, this in the form of thermal energy from gas combustion. Thanks to high Capex and Opex, the levelised cost to removing a tonne of CO₂ through DAC today is often over $500.

CO₂ captured though DAC can be either be stored or put to work. Classic CO₂ storage targets are underground injection into depleted fossil fuel reservoirs, saline aquifers or ultramafic rock formations. In each case, the cost of compression, transportation, injection and monitoring needs to be factored into lifecycle analyses for DAC based removal. CO₂ uses include synthetic fuels, construction materials or plastics. However these can only be considered carbon negative if CO₂ is not re-released.

The DAC industry remains in its early infancy. In 2021 there are fewer than 20 DAC plants in operation worldwide removing a total of just ~12,000 tCO₂/year². That’s enough to offset the annual carbon footprint of only 773 average people in the US. We have a long way to go. The good news is that the DAC space is alive with innovation; we expect to see leaps forward in efficiency and cost over the coming years. In the meantime, it’s important DAC doesn’t become a pretext for avoidable emissions or at the expense of lower cost removal pathways

Benefits

• Potential for very long-term carbon storage

• Excellent additionality, measurability and verification

• Theoretically highly scalable with less competition for land and water than some other pathways

• Location independent - can be optimised for energy and CO₂ sequestration availability.

Methods: 

• Solid sorbent, often functionalised with amines

• Liquid solvents

• Open-air mineralisation

• Electrochemistry

• Temperature/Pressure/Electro/Moisture swing.

Issues (we care about)

• Realistic routes to scale with efficiency

• Responsible use of resources including land, water and above all energy, minding risks of displacing renewables from the grid or creating new demand for natural gas

• Sensible storage or usage that locks up carbon permanently

• Design modularity and implications for strategic financing.

Sources

1. Negative emissions—Part 2: Costs, potentials and side effects, Fuss et al. 2018

2. Counteract estimate based on IEA data and 2021 new plant launches