Co-assessment of costs and environmental impacts for off-grid direct air carbon capture and storage systems

Abstract

Large-scale deployment of direct air carbon capture and storage (DACS) is required to offset CO2 emissions. To guide decision-making, a combined assessment of costs and environmental impacts for DACS systems is necessary. Here we present a cost model and life cycle assessment for several combinations of off-grid DACSs, powered by photovoltaic (PV) energy and heat pumps combined with battery storages to mitigate intermittency of the PV energy source. Utilization factors of DACSs are estimated for different locations, power of PV systems and battery capacities. We find that the cost optimal layout for a DACS in Nevada (USA) with a nominal CO2 removal capacity of 100,000tCO2 per year consists of 100 MW PV and 300MWh battery. Costs are $755 and $877 for gross and net removal of 1tCO2. The cost difference is explained by a carbon removal efficiency (CRE) of 88%. Of 16 evaluated environmental impact categories mineral resource use is most problematic. We conceive a dashboard which allows to track how changes to technical parameters, such as energy consumption or adsorbent degradation, impact costs, CRE and combined environmental impacts. In an optimized scenario and including tax credits, costs for net-removal of 1tCO2 will be $216 at a CRE of 93%.

Managing intermittency of renewable power in sustainable production of methanol, coupled with direct air capture

“…With regards to the cost of solely performing DAC, independent of methanol synthesis, a recent study by Gutsch and Leker 86 examined DAC with carbon sequestration (DACCS) when operating dynamically with off-grid solar PV power, estimating an optimised net CO 2 removal cost of $877 per t CO 2 , falling to $216 per t CO 2 with technology improvement and favourable project financing. Standalone DACCS, therefore, does capture CO 2 at a lower net cost than DAC-PtM (Table 4), although the cost range reported by Gutsch and Leker remains far above even the highest current CO 2 prices of ca.…”

“…Improvements in the energy efficiency of DAC-PtM are possible through the substitution of direct electrical heating in low-temperature DAC with heat pumps as considered in other work, 86,98 for which heat at B100 1C is requiredtowards the upper-end of temperatures currently delivered by state-of-the-art heat pumps, sacrificing their coefficient of performance. 111,112 In decreasing the plant energy requirement, heat pumps would serve to reduce the required size of a wind farm for electricity provision.…”

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“…Without taking into account energy gained in enthalpy change for a given area of cyanobacterial cultivation, the overall mass of CO 2 sequestered and converted into biomass per square meter of solar irradiance is significantly less than the mass of CO 2 that would be separated from the air by employing a given atmospheric carbon removal technology using photovoltaics. Assuming that a PV panel can power a given atmospheric carbon removal method that uses 1,250 kWh/T CO 2 to perform separation, if the energy is produced from a m 2 of photovoltaic panels, assuming that there is a 100% energy transfer efficiency between the PV panel and carbon removal and Leker, 2024). Comparing this to cyanobacterial cultivation, 43.3 g/m 2 /d of biomass yield was achieved using an outdoor ponddesign photobioreactor with Synechococcus elongatus UTEX 2973 in September 2021 in Texas at a similar latitude, an equivalent CO 2 fixation of 81 g/m 2 /d, assuming a biomass to CO 2 stoichiometric ratio of 1:1.88 (Long et al, 2022).…”

“…Therefore, a strong argument exists based on thermodynamics to use engineered bacteria to produce carbon sinks as a method of deriving chemical (and economic) value from this enthalpy change instead of the burial of carbon, even if only partially. Secondly, even if we were to, for the sake of argument, nullify the energetic gain as a sunk cost, the cost of deploying a fully PV powered DAC infrastructure imposes a levelized cost of capture of $877/T CO 2 based on recent models (Gutsch and Leker, 2024). Conversely, an algal system amounts to $320/T CO 2 (calculated from the minimum biomass selling price of $602/T biomass) based on NREL's technoeconomic analysis which assumes a modest average of 18.5 g/ m 2 /d of annual productivity (Klein and Davis, 2023), before any consideration of possible additional revenue routes from engineered carbon sinks and bioproducts.…”