Power to Gas (P2G) systems aim to store surplus renewable electricity generated in the form of gaseous fuels such as hydrogen or methane. The concept is ideal for storing the surplus energy for long periods in gaseous form and can be used in the future for desired end applications, i.e. either in gaseous form or electricity. In the P2G process, the surplus renewable energy converts into methane (gaseous form) in a two-step process: electrolysis followed by methanation. The electrolysis process is used as the source for hydrogen generation, which further reduces carbon dioxide to produce methane. In this review, different electrolyzers and methanation processes are compared for the P2G process. The major process parameters and hydrogen gas-liquid mass transfer are discussed by comparing different process conditions and reactor configurations used in biological methanation. An understanding of the techno-economic analysis indicates that cost of the hydrogen generation is the key factor that determines the overall economics of the P2G system. The cost of hydrogen generation is associated with the capital cost of the electrolyzer and the cost of the electricity. It is expected that once this technology becomes mature, the economics of P2G systems will improve in the future

Keywords: Power to gas, Renewable electricity, Renewable natural gas, Methanogens, Carbon dioxide