Abstract
Energy storage is essential for transitioning to a renewable system based on renewable sources. To meet this challenge, Power-to-X technologies are attracting more attention. This work explores converting the excess of electric energy obtained from wind or solar sources into hydrogen and then into methane leveraging existing natural gas infrastructure for easier storage and transport. The process involves two stages: Firstly, the methane production step using Power-to-X technologies during excess renewable energy periods and, secondly, the electricity generation step during high demand with CO2 capture for reuse in methane synthesis, forming a closed carbon loop. In this way the Power-to-X process is integrated with repurposed combined cycle power plants (CCPPs) creating a Power-to-methane-to-power system. Two approaches are evaluated: oxy-combustion, which simplifies process CO2 purification and air combustion, which needs a more complex CO2 purification, such as amine absorption or PSA systems. The results show that ordinary combustion capturing CO2 by amines is the most profitable process, especially when it is assumed that the oxygen produced by the electrolyzer is sold. For a CCPP with a nominal capacity of 400MW, the cost of electricity production ranges from 450 $/MWh to 490 $/MWh when the income from oxygen sales is neglected. If the oxygen produced can be fully absorbed by the market, the electricity production cost decreases to 250 $/MWh and 300 $/MWh.