In light of the need to reduce CO2 emissions from fossil fuel use, increased use of renewable energy has become one of the strongest available energy alternatives to date. However, one of the main issues slowing the penetration of renewable energy is its intermittent availability. A cost-effective and dependable bulk energy storage (BES) technology will be a critical component of the electric grid going forward. Furthermore, while solutions are being sought to quickly decarbonize the energy system, carbon capture and storage (CCS) technologies have been proposed as an effective tool to limit CO2 emission from the use of fossil fuels. The deployment of CCS technologies has been slowed, however, by the lack of a regulatory or market driver and the high cost of the technology. For these reasons, increased effort has recently been focused on finding strategies for alternative use of CO2 that could provide a potential offset for the cost of CCS, with the main goal of helping to accelerate its deployment.
Use of carbon dioxide for energy storage has been proposed as a concept that could help develop better BES systems while using CO2, potentially providing a most needed offset for the cost of CCS. This proposition becomes more attractive if it has the additional potential of being combined with long-term geologic sequestration (GS) of CO2.
This report reviews the ideas proposed so far on the use of CO2 for energy storage in subsurface schemes, with the focus on two questions: 1) is the scale of CO2 utilization meaningful to provide economic benefits to the energy storage scheme and/or CCS deployment and 2) do the proposed ideas have the potential to be combined with long-term GS of carbon dioxide?
From this review, it seems likely that using CO2 for energy storage might be feasible only at small to moderate scales, with minor economic or storage potential for CCS operations. However, all the ideas to date are at an early stage of development, and most of the studies so far use simple models with assumptions that could greatly affect their feasibility and impact.