Retrofitting existing combined cycle power plants to enable carbon circularity through Power-to-Methane energy storage

Abstract

[EN]Energy storage is a critical component in the transition to a renewable based energy system. To face this challenge, Power-to-X technologies are gaining increased attention. This study investigates the conversion of surplus electricity from wind and solar sources into hydrogen, and subsequently into methane, utilizing existing natural gas infrastructure for efficient storage, transport and conversion into electricity. The process consists of two main stages: first, the production of methane using Power-to-X technologies during periods of excess renewable energy production. Second, the generation of electricity during peak demand, with CO2 captured for reuse in methane synthesis creating a closed carbon loop. This integrated system repurposes combined cycle power plants, developing a Power-to-Methane-to-Power (PtMtP) configuration. Two alternative combustion approaches are evaluated: oxy-combustion (OC), which simplifies CO2 purification and air combustion or ordinary combustion or conventional combustion (CC), which requires more complex purification methods such as amine absorption or pressure swing adsorption (PSA). Results indicate that CC with CO2 capture via amine absorption is the most profitable process, especially when it is assumed that the oxygen produced by the electrolyzer is sold. For a 400 MW CCPP, the electricity production cost ranges from 650 to 750 $/MWh when the income from oxygen sales is neglected. However, if it is assumed that the market can absorb the full output of electrolytic oxygen, the production cost decreases to between 450 and 550 $/MWh.