Technologies that remove CO2 directly from air offer enormous promise to help fight climate change. Since the world agreed to ambitious long-term climate goals at COP21 that suggest a large role for negative emissions technologies, major media outlets have ramped up their coverage of the direct air capture technologies (e.g. Washington Post, Wall Street Journal, Bloomberg Business, and Forbes). But from my recent conversations with industry and government carbon capture experts, much skepticism still remains about the role that direct air capture systems should play in our response to climate change today. Below is a Socratic dialogue about direct air capture between an open-minded skeptic and a reality-based proponent.
Skeptic: I like the idea of direct air capture technology in theory, but isn’t it really expensive in practice?
Proponent: That is a reasonable question to which there is no good answer today. Entrepreneurs in the field will tell you that costs for early pilot projects are expensive (e.g. $250-500/t), but that costs can be competitive (between $50-100/t of compressed CO2) once direct air capture systems are manufactured at scale. Solar PV in the 1980s can provide an analog: costs for PV panels have come down by nearly two orders of magnitude over the past 30 years.
Unfortunately, entrepreneurs have not yet published auditable cost figures for their initial pilots. And only a few direct air capture projects have been built, so we won’t be able to confirm the slope of the cost reduction curve without further deployment.
If entrepreneurs can bring costs down around $100/t of CO2, it is reasonable to expect these technologies to gain adoption--this price is roughly the price we pay for other climate mitigation policies such as California's Renewable Portfolio Standard and its Low Carbon Fuel Standard.
Skeptic: But won't other alternatives for direct air capture like advanced bioenergy (with CO2 capture from the production process) continue to come down in price, making direct air capture uneconomic even at those long-run cost targets? Direct air capture systems have only received around $3 million in cumulative research and development funding from the U.S. Government compared to the billions spend on next generation biofuels and point-source carbon capture and storage (CCS).
Proponent: We simply don't know whether next generation bioenergy and/or point-source CCS systems will be able to be inexpensive, low-carbon, and land efficient (i.e. not competing for land with food production or ecosystem conservation)--even with billions of dollars of support going into the development of these technologies. For that reason, direct air capture offers an important hedge against sustainable bioenergy systems failing to deliver on their promise, as direct air capture systems are relatively land efficient, and can be cited in agriculturally poor areas.
But the question of whether direct air capture can compete against advanced bioenergy production might be the wrong question altogether. Direct air capture systems may prove synergistic with bioenergy production, as biofuel routes such as algae production function best at elevated CO2 levels, which requires a supply of dilute CO2. Direct air capture systems can produce dilute CO2 at much more competitive rates than they can produce more concentrated CO2. And because direct air capture systems can be sited anywhere, they can enable bioenergy facilities to be cited more flexibly and thus operate more cost-effectively.
Skeptic: But in terms of supplying CO2 for use in industrial processes (such as biofuels or even synthetic fuels production), direct air capture has to compete against myriad other industrial sources that produce higher CO2-concentration exhaust streams. For example, the atmosphere is 0.04% CO2 compared to coal power plant exhaust gas streams of 10-15% and natural gas power plant exhaust gas streams of around 5%. Thermodynamic laws dictate that lower concentrations of CO2 require more energy to produce concentrated CO2. This is begs the question: if we can capture CO2 directly from the air, can’t we employ similar processes to capture CO2 from industrial exhausts but at lower costs? Even if CO2 sources are located far from CO2 utilization/sequestration sites, CO2 is fairly inexpensive to transport via pipeline: thousands of miles of CO2 pipelines already exist across the central US, and costs on the order of $10/t.
Proponent: In some cases, CO2 transportation from power plant to a utilization or sequestration source is very expensive—trucking CO2 can cost upwards of $100/t. In these cases, direct air capture systems that can be sited directly at the utilization or sequestration site could make economic sense (assuming there is a source of low-carbon energy nearby).
And in the long-run, we might need to capture and sequester more CO2 than is emitted from industrial sources to meet negative emissions targets. In this event, direct air capture will be valuable as a complement to other forms of industrial-source CO2 capture.
Skeptic: Even if direct air capture has a long-run option value, we are a long way off from reducing all of the industrial-source CO2 emissions. Why should we focus on developing direct air capture technology today, especially when direct air capture systems require carbon-free energy that could otherwise be used to displace emissions from the electricity sector?
Proponent: Direct air capture technology will likely take decades to reach long-run cost targets. Unless we get started today, we might not have affordable, scalable direct air capture technologies when we may need them in a few decades. In the meantime, some direct air capture technology developers are employing clever approaches to utilize waste heat (which cannot efficiently be converted into electricity) to power their technologies. Direct air capture systems could also serve as a variable load resource that could actually help integrate larger amounts of intermittent renewable energy into the grid (i.e. by turning on direct air capture when there is excess power production, and turning the systems off when other demand for power is high).
Skeptic: Even if direct air capture systems are using “non-rival” renewable energy and will take decades to reach scale, every dollar spent on direct air capture R&D is a dollar not spent on the development and deployment of other climate strategies (such as solar, wind, industrial point-source CO2 capture, etc.). Isn’t the opportunity cost of investing in direct air capture too high?
Proponent: The best argument for starting the development of direct air capture today is that a diverse portfolio of investments usually performs better over the long run, and direct air capture is largely absent from the climate mitigation solutions portfolio today. There is a real option value for direct air capture as a hedge against advanced bioenergy scalability and as a complement to renewable energy deployment (as a variable load for intermittent renewables and as a CO2 supply for advanced biofuel production), which means that we should be investing some fraction of our clean energy budget in the development of these technologies today. Targeted research and development spending on direct air capture today can answer critical questions about the viability of these technologies, and we can rebalance our portfolio over time to invest more or less in these technologies once we have updated information about their value.
Skeptic: But won’t we need to spend a lot of money on direct air capture research and development to learn whether it can play a large role in the fight against climate change?
Proponent: Again, no great answer to this question exists today, as no direct air technology commercialization roadmap has been published. Professor Klaus Lackner of the Center for Negative Carbon Emissions at Arizona State University has said around $100 million of government funding would go a long way in commercializing direct air capture systems. If this $50 million technology prize for direct air capture that was introduced by Senators Barrasso and Schatz gets passed into law, then the US Department of Energy (DOE) could reach this $100 million target fairly easily with increased funding through the Fossil Energy department’s grant budget for research, the Bioenergy Technology Office’s funding for advanced biofuels utilizing direct air capture as a CO2 source, and the creation of an ARPA-E program dedicated to direct air capture technology innovation.
Proponent: I hope you will see that I'm not advocating for massive investments in direct air capture instead of investments in other climate mitigation solutions, but rather for targeted research and development into air capture technologies today that enables us to learn how valuable these solutions are without wasting money.
Skeptic: I'm still skeptical of direct air capture ever reaching this potential, but this seems like a reasonable approach to me.
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