Direct Air Capture (DAC)

DAC plants by Climeworks

Direct Air Capture: A necessity to limit temperature rise to a 2°C goal.

What is Direct Air Capture? It is best to think about DAC "plants" as artificial or mechanical trees that capture CO2 directly from the air. This captured CO2 can then be compressed and sequestered, or it can be converted into useful products. DAC is a promising technology, and falls under the bigger group of negative emissions technologies (NETs), which all remove CO2 in some form or the other. NETs, including DACs, form a crucial part of the solutions portfolio to reach the goal of 2°C temperature rise.

How is the CO2 captured from the air? There are two major technologies [4]. The first one is where air is passed through chemical solutions, which remove the CO2 and return the remaining air back to the atmosphere. The second one involves solid sorbent filters that chemically bind CO2, and release CO2 when they are heated. The second technology is used by Climeworks.

Workings of Climeworks Technology [1]

How much can DACs help? It has been estimated that by 2050, DACs will remove CO2 in the range of 0.5 - 5 billion metric tons CO2 per year worldwide [3]. We take a middle value of 2.5 billion metric tons worldwide and that the United States will be responsible for 10% of the worldwide value (We choose 10% for USA even though it is 4.3% of the worldwide population, because USA is a developed country with numerous resources to implement DACs). We calculate that DACs will remove 0.25 GtCO2/yr by the year 2050. This can be seen to form a large part of the total reduction goal of 3 GtCO2/yr by 2050.

Won't such a technology use a lot of resources? In comparison to numerous other NETs, DACs actually use much less resources in terms of both land and water. Climeworks, the world's leading DAC company, estimates a non-arable land requirement of 6,200 hectares (ha)/GtCO2 for the DAC plants themselves, and about 200,000 ha/GtCO2 if we include the required renewable energy production, all from solar [6]. For our purposes of 0.25 GtCO2/yr, we estimate needing 50,000 ha of land if all energy for the DACs plants comes from solar energy. Furthermore, if Climeworks' plants/technologies are used, they estimate that instead of using any water, we produce (due to the vapor taken from the ambient air) 1 cubic meter of water per ton CO2, i.e. 250 billion liters of water for 0.25 GtCO2 [2].

While, this is extremely hopeful, the energy requirements of DACs can be a source of concern. Future projections based on current technology estimate that DACs will need around 2,000 kWh/tCO2 (400 kWh electrical and 1,600 kWh thermal) [6], which means we will need 500 billion kWh to remove 0.25 GtCO2/yr. The only way we can do this is by using renewable energy sources, and this is why we require the extra land, for example for solar panels. What helps is that solar energy prices are continuously falling, allowing for the price of DACs to reach about $100/tCO2 in the next 10 years [6].

Energy needs for DAC technologies for CO2 use and storage

DACs on 50,000 ha of land can remove 250 million tons CO2/yr, and produce 250 billion liters of water, all while being powered by solar energy!

Are we ready to use DACs? The Technology Readiness Level (TRL) for different DAC plants is usually around 6 (verification using demonstrator in an application-relevant environment), but certain low temperature DAC plants, specifically those belonging to Climeworks have a TRL of 9 (successful commercial deployment) [2]. This is because Climeworks operates demonstration projects in Zurich, Rapperswil, and Hinwil (Switzerland). Carbon Engineering, another DACs company, is working with Occidental Petroleum in the US to build a DACs plant which can be operational by 2023, and will remove unto 1 MtCO2/yr [4]. However, it will take time to scale up the process to able to remove 0.25 GtCO2/yr, and therefore, we project 2050 as the year by when we can reach this potential.

Will everyone accept this technology? To date, there have not been any thorough studies which discuss the social acceptance of DACs [2]. Therefore, more in depth research is required to understand the level of acceptance of this NET and also any obstacles that might come in the way of its implementation. Potential arguments could be energy demand, concerns about geologic storage, and enhancement of oil recovery (since that can promote more fossil fuels) [3]. Questions like why trees can’t simply replace DACs are a common sentiment, and the land/water requirements of both can be compared (check out the afforestation blog!), to show how important DACs are.

What are some proposed policies? DACs, a comparatively new commercial technology, still has numerous policies building around it. The new plant being built by carbon engineering is large enough to be eligible for:

1. 45Q tax credit: Would provide $35/tonne of CO2 used in enhanced oil recovery and $50/tonne for CO2 storage [4].

2. California Low Carbon Fuel Credit: Credits traded at around USD 180/tCO2 in 2019 (if the captured CO2 is used to produce low carbon transportation fuels) [4].

To promote further building of DAC plants, the following can also be considered:

1. Leveraging Federal Procurement - For example, the Department of Defense can increase competitive procurement of DAC based fuels form 0 to 23% of 2017 operational fuel consumption [8].

2. Integrating DAC with sequestration in carbon pricing: Some sort of cap-and-trade or carbon tax can help [8].

3. Partially/fully fund comprehensive Research, Development, and Demonstration (RD&D) programs.

4. Further research into finding combinations of available land to build DAC plants and geologic storage locations.

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To know more about Climeworks and their work, watch this short video by Christoph Gebald, director and co-founder of Climeworks!

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References:

1. https://climeworks.com/ (accessed Dec 2, 2020).

2. Viebahn, Scholz, Zelt, P. A. O. The Potential Role of Direct Air Capture in the German Energy Research Program—Results of a Multi-Dimensional Analysis. energies 2019.

3. Fact Sheet: Direct Air Capture. https://www.american.edu/sis/centers/carbon-removal/fact-sheet-direct-air-capture.cfm (accessed Dec 3, 2020).

4. Iea. Direct Air Capture – Analysis. https://www.iea.org/reports/direct-air-capture (accessed Dec 3, 2020).

5. Direct Air Capture and Storage. https://energyinnovation.org/2019/09/16/direct-air-capture-and-storage/ (accessed Dec 3, 2020).

6. Beuttler, C.; Charles, L.; Wurzbacher, J. The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions. https://www.frontiersin.org/articles/10.3389/fclim.2019.00010/full (accessed Dec 3, 2020).

7. IEA, Energy needs for DAC technologies for CO2 use and storage, IEA, Paris https://www.iea.org/data-and-statistics/charts/energy-needs-for-dac-technologies-for-co2-use-and-storage

8. Larsen, J.; Herndon, W.; Grant, M.; Marsters, P. Capturing Leadership: Policies for the US to Advance Direct Air Capture Technology. https://rhg.com/research/capturing-leadership-policies-for-the-us-to-advance-direct-air-capture-technology/ (accessed Dec 7, 2020).