The high costs of BECCS and DACCS, because of their high energy input requirements, are likely to amplify the growing narrative that net zero is ‘unaffordable’.
So far, this paper has explored how future reliance on engineered removal technologies – chiefly BECCS and DACCS – has increased, and that due to shifting geopolitics, conflict and historically low investment in upstream oil and gas, there has been growing scrutiny of the cost of net zero, and a recent shift in focus towards energy security and affordability. This chapter focuses on why BECCS and DACCS are likely to be a very expensive component of net zero and the energy transition. This raises the question of what might be the most cost-effective way of pursuing engineered CO₂ removals.
With the UK, in 2024, granting development consent for the world’s largest BECCS facility, it is interesting to note that the most recent analysis by the UK’s Department for Energy Security and Net Zero on the costs of all electricity generators states:
Given that the costs are yet to be fully understood, the risk is that future engineered removals costs could be incompatible with a focus on energy security and affordability, and that therefore the reliance countries have already built in cannot be fulfilled. This would widen the emissions gap and increase the likelihood of triggering accelerated climate change.
Engineered removals, deployed at scale, bring multiple risks in terms of land-use tensions, supply-chain emissions and carbon debt pertaining to BECCS (summarized in Box 1). However, the primary near-term risk is that reliance on engineered removals technologies will be unduly costly, requiring subsidies paid for by taxpayers or energy consumers, or via carbon markets with costs again, ultimately, passed on to consumers via increased prices of goods and services.
Huge energy requirements
In its simplest terms, within both BECCS and DACCS systems, the CO₂ removal or separation process requires a chemical to bind to the CO₂ molecule. Because a significant volume of that chemical agent is required, it must be recycled around the system. This means that a significant amount of heat energy has to be applied to the chemical to allow it to release its CO₂, which is then subsequently buried underground. This is where the large energy requirement for both systems emerges.
Given that the costs are yet to be fully understood, the risk is that future engineered removals costs could be incompatible with a focus on energy security and affordability, and that therefore the reliance countries have already built in cannot be fulfilled.
It is important to note that whereas DACCS will be a net energy consumer, BECCS is likely to be a net energy producer, albeit with significant amounts of energy being diverted to the CCS equipment.
DACCS removes carbon from ambient air via a chemical medium – typically an aqueous alkaline solvent or sorbent – in a similar manner to the solvents used in the CCS process of BECCS. The chemical medium is subsequently stripped of CO₂ by applying heat and then CO₂ dehydration and compression, allowing the medium to be reused to bind to more CO₂. The two main DACCS technologies are solid or liquid sorbents.
The first and second laws of thermodynamics show that separating one gas from another requires a significant energy input. Because CO₂ is more concentrated within the flue gases of a power station, compared with that of ambient air, a BECCS system producing electricity will require less energy per unit of CO₂ captured, relative to a DACCS system which sucks in and processes atmospheric gases.
Importantly, the energy requirement of both BECCS and DACCS is primarily heat. While the heat energy input for BECCS will always be biomass, DACCS can, in theory, use various energy sources to produce the heat requirement. However, converting electricity to heat is a relatively expensive. As such, renewable heat sources will likely be needed for DACCS. While there are renewable heat sources such as from biomass and geothermal, these are much more limited in their current deployment and future availability than electricity-producing solar and wind.
Liquid DACCS (L-DACCS) relies on an aqueous solution (such as potassium hydroxide), and requires high temperatures of 300–900°C in the CO₂ separation process. Solid DACCS (S-DACCS) uses highly porous solid sorbents with a high surface area to adsorb the CO₂ molecules, and requires relatively lower temperatures of around 100°C. Because the energy input and hence costs of L-DACCS are higher, many of the DACCS projects in R&D and early commercialization phases are S-DACCS.
In Iceland, notably, operations began in May 2024 at S-DACCS specialist Climeworks’ second large-scale commercial facility, Mammoth. Like the company’s first facility, Orca, which entered production in 2021, Mammoth derives its heat source from the country’s abundant geothermal resources.
Within the relatively low-temperature S-DACCS system, to capture and store 1 million tonnes of CO₂ requires around 2 terawatt hours per year (TWh/yr) of energy. This is equivalent to the output of a 230 MW gas turbine running constantly for a year. (For reference, the UK’s largest gas power station has five 400 MW turbines.) Of this energy, more than 85 per cent is in the form of heat. For the high temperature process of L-DACCS, the energy needed to capture and store 1 million tonnes of CO₂ increases to 2.4 TWh/yr, with more than 75 per cent being in the form of heat.
In a BECCS system, the heat input to release the CO₂ molecule from the chemical solvent, within the CCS equipment, comes from diverting heat from the combusted biomass that would otherwise produce electricity, this is commonly referred to as the energy penalty.
The important consequence of the high heat energy input requirements of engineered removals is that they comprise nearly 50 per cent of the cost of DACCS, and at least 33 per cent of the cost of BECCS. It should be noted that the latter figure (i.e. for BECCS) is based on the UK government’s ‘low’ cost of wood pellet price scenario; under the ‘central’ scenario, the figure would rise to at least 45 per cent of the cost.
Current and future abatement costs of engineered removals
A 2023 Oxford Institute for Energy Studies report estimates that current pre-subsidy costs for DACCS are around $800–$1,000/tCO₂. This would mean that if DACCS were to provide 100 per cent of the engineered removals 2050 level within the IPCC’s Sixth Assessment Report (AR6) (i.e. 2.77 GtCO₂/yr), some $2.2–$2.8 trillion would be required every year to finance DACCS. However, Climeworks expects costs to decline to $400–$700/tCO₂ by 2030, and to $100–$300/tCO₂ by 2050, meaning that by 2050 the annual finance requirement could be in the range of $277–$831 billion.
The declines in costs anticipated by Climeworks are predicated on technological innovation, but are also limited by the high fuel input costs. While it is unclear in which regions Climeworks expects its technology to be able to operate in these cost ranges, any suitable country will evidently require abundant and low-cost renewable heat sources, similar to the geothermal heat sources found in Iceland.
In January 2024, Drax, the main UK developer of BECCS, published guidance for the subsidy requirement to stimulate ‘material deployment of BECCS’ in the US, stating that ‘further increasing the 45Q tax credit [for carbon sequestration] to $100–150/t CO₂ did not lead to a material deployment of BECCS but rather boosted the uptake of coal-CCS’; and that ‘negative emission credits of 30 to 40 $/tCO₂ sequestered is required for carbon dioxide removal technologies in addition to the 85 $/tCO₂ provided by 45Q’. Therefore, a current subsidy for BECCS of around $120/tCO₂ would be required. While biomass wood pellet prices have risen recently (see below), some assessments, like the International Renewable Energy Agency’s (IRENA) in 2021, envisage that BECCS costs may fall over time, reaching $69–$105/tCO₂.
Assuming, as the IPCC does, that BECCS accounts for 99 per cent of the 2050 engineered removals sequestration rate, this would mean engineered removals would cost between $192 billion and $295 billion annually. However, if the costs of BECCS do not fall in line with current expectations, and the primary source of feedstock for BECCS is wood pellets (see Box 1), the high end of the range could be $315 billion annually. This is based on the mid-point of Drax’s January 2024 estimate of the US subsidy requirement, with wood pellets comprising 50 per cent of the global feedstock for BECCS.
For BECCS and DACCS respectively, 33 per cent and 50 per cent of ongoing costs are energy input operational expenditure.
Given the current heightened scrutiny of the cost of net zero, and the focus on energy security, potential costs of engineered removals, primarily BECCS, in the range of $192–$315 billion annually by 2050 need to be set in the context of current and projected global spending on the energy transition. Around $1.77 trillion per year is currently spent on the energy transition, globally. To reach net zero in 2050, the IEA anticipates that around $4 trillion will need be needed every year between 2030 and 2050, with the Energy Transition Commission anticipating that, on average, $3.5 trillion in capital investment will be needed each year between now and 2050. This means that engineered removals would account for some 5.5–9.0 per cent of all clean energy investment in 2050, based on the IPCC 2050 removal potential of 2.77 GtCO₂/yr. It is important to emphasize that this range does not factor in the cost to energy consumers of the electricity produced by BECCS, or that, as explored in the next section, wood pellet prices have risen in recent years.
Emissions reductions of 2.77 GtCO₂/yr could be achieved for around $72 billion annually from electric vehicles (EVs), solar and onshore wind, based on their respective 2050 weighted abatement costs, or 2 per cent of the average yearly spend to 2050. Here, it should be noted that as the global emissions gap widens CO₂ removal will become more important relative to mitigation. Importantly, because of the lifetimes of these assets, the majority of the costs are not ongoing operational expenditure (opex), unlike for BECCS and DACCS, where 33 per cent and 50 per cent, respectively, of their costs are energy input opex.
Not only do engineered removals require high fuel opex, which is undesirable in the context of the ongoing focus on energy security and price, BECCS deployment costs are unlikely to benefit from high learning rates. Technologies with high learning rates, and therefore fast cost reductions, tend to be modular, with – as for solar panels, wind turbines and lithium-ion batteries for EVs, for instance – thousands to millions of units able to be produced each year. Such technologies have already demonstrated, and continue to demonstrate, rapid cost reductions. BECCS, however, is generally being considered as a retrofitted technology, whereby large CCS infrastructure is fitted to existing bioenergy power stations or coal power stations with fuel switching. As such, at most hundreds of BECCS facilities are likely worldwide. This means the opportunity for engineers and contractors to learn from project to project, improve build efficiencies and drive down costs is more limited.
