Latest data show that the 1.5 C level for the average temperature anomaly targeted in the Paris Agreement has already been reached. Although the El Niño may have contributed much to warming spikes in the last years, warming records are broken continuously. This means that transitioning to a highly renewable energy system is no longer sufficient to comply with the 1.5 C target, and CO2 has to be actively removed from the atmosphere.
Carbon dioxide removal (CDR) can have two different effects on system level: Offsetting remaining fossil emissions or creating a net-negative emission system. The latter is the preferred option, as offsetting fossil emissions does not reduce the negative effects of elevated CO2 levels, while deep defossilization and transitioning to a highly renewable energy system brings many environmental, health, and economic benefits. Solar PV may be a key enabler of CDR globally, because of very promising cost prospects and high capacity density.
Area demand of technological versus bio-technical CDR
The transition of energy systems is often seen to be limited by the available area for renewable energy capacities. While for some regions such as South Asia or densely populated regions of Europe and Southeast Asia the situation is indeed worth having a closer look, no real constraints for the land availability could be identified yet. However, if large-scale CDR is to be implemented with technological (direct air capture and carbon sequestration, DACCS) or bio-technical (bioenergy with carbon capture and sequestration, BECCS) options, the question arises whether the area demand suffices to power both a highly renewable energy-industry system and also additionally large-scale CDR. After all, technological CDR needs to run on renewable energy, and bio-technical CDR needs a significant amount of biomass, while sustainable residues will not be sufficient.
In a recent study “Area demand quantification for energy system-integrated negative emissions based on carbon dioxide removal portfolios” published in Environmental Research Letters, this question has been dedicatedly addressed. The study distinguishes between gross and net area demand. Gross area demand includes the entire area for energy supply including spacing, gathering area, etc., while the net area demand only includes either used-up area that is locked from co-use such as agriculture or forestry, or which is deemed to have negative effects on biodiversity, such as short rotation energy crops. The latter is important for bio-technical CDR, as large-scale BECCS will only be possible via energy crops, as sustainable residues may have more value in other areas of the energy-industry system. The underlying energy system is largely based on solar PV and wind power as the main future energy sources.
Energy crops (left) and solar PV power plants (right) both require area. Technological CDR powered by renewables such as solar PV outperforms biomass-based bio-technical CDR options due to higher energy density. Images: Lignovis GmbH, Jeffrey Beall, Wikimedia Commons, CC BY-SA 4.0
The study identifies significant differences between technological CDR portfolios largely run on solar PV electricity, and CDR portfolios with a high share of bio-technical options for the 1.5 C target. The biomass-prioritizing portfolio shows high values of both gross and net area demand, while especially the high net area demand of 2.8 million km2 globally, while technological CDR portfolios dependent on DACCS powered by a large share of solar PV show 1.3 million km2, both figures including the entire energy-industry system’s energy supply. For an even more ambitious climate target of 1.0°C the gross area demand increases for all portfolios due to higher dependency on afforestation, while the net area demand suggests that technological options powered by renewables such as solar PV is preferrable from an area demand’s point of view. The increasing development in solar PV technology largely contributes to this conclusion. Low-cost solar PV can also be used for seawater desalination to enable afforestation in arid or even desert regions for long-term CDR.
The role of solar PV for scaling a CDR industry in Iceland
Iceland has unique features that may enable a large-scale CDR industry in the country. Its geological composition makes it very suitable for in-situ mineralization, where CO2 is dissolved in water and pumped underground in porous basalt, where it turns in a relatively short time to minerals, locking away the CO2 in a secure way for a long time. The heat for direct air capture (DAC) can be provided by low-cost geothermal plants. The feasibility of this concept has already been demonstrated in the CarbFix project.
Whether a large-scale CDR industry in Iceland is possible, and what possible bottlenecks may be present, have been addressed in a recent publication “Seeking El Dorado: Iceland’s carbon dioxide removal service opportunities to meet global demand and a new lens on overnight transition cost” published in Gondwana Research. The authors applied different scaling targets for CDR in Iceland, varying the availability of geothermal energy to identify the roles of other, not yet explored renewable energy options such as solar PV in these scenarios.
The results identified an interesting role for solar PV even in the harsh Nordics close to the Artic Circle. To provide low-cost electricity for the baseload CDR demand, the optimization suggested a key role for solar PV to balance reduced wind power production during the summer with solar PV electricity, which is abundantly available during the summer in the far North. Although an increased demand for CDR with a significant baseload demand profile drives the cost for energy, the scenario with flexible CDR demand oriented on the availability of renewable energy did not reduce the cost, due to large required capacities. Overall, the levelized cost for carbon dioxide removal can be kept relatively stable under €60 /tCO2, also due to the low-cost character and overall competitiveness of solar PV in countries such as Iceland.
Solar PV as the working horse of future system
Many sectors have already been identified to benefit from low-cost solar PV electricity, while low-cost batteries support such conclusions. Indicative research suggests that solar PV may also play an important role in the CDR sector also with a positive impact on environmental, social, and governance criteria of CDR. Technological improvements beyond the efficiency such as single-axis tracking, bifacial technology, or floating structures further push for ever-increasing shares of solar PV in modern energy systems. Solar PV is indeed the new king, and the world is set to enter the multi-terawatt era.
Authors: Dominik Keiner, and Christian Breyer
This article is part of a monthly column by the LUT University.
Research at LUT University encompasses various analyses related to power, heat, transport, industry, desalination, and negative CO2 emission options. Power-to-X research is a core topic at the university, integrated into the focus areas of Planetary Resources, Business and Society, Digital Revolution, and Energy Transition. Solar energy plays a key role in all research aspects.
The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.
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