Thermodynamic and economic analysis of a directly solar-driven power-to-methane system by detailed distributed parameter method

The transformation of solar energy into easily transportable and storable fuel brings a prospective solution to the issue caused by its intermittency and non-dispatching. Relying on well-established infrastructures and mature technologies for application, methane can be an attractive energy carrier for improving the penetration of solar energy in the future energy structure. To evaluate the feasibility of solar-to-methane from technical and economic views, this paper proposes a directly solar-driven power-to-methane system integrating photovoltaic plant, solid oxide electrolysis cell, methanation reactor, and membrane module. The detailed distributed parameter method is employed for thermodynamically modeling the core components of the system to consider the profiles of current density, temperatures, and composition concentrations. A comprehensive thermodynamic and economic analysis is further conducted for the system, and the results indicate that the power-to-methane efficiency, total energy efficiency, and total exergy efficiency of the system can reach 68.41%, 9.88%, and 11.08%, respectively. With the annual average solar radiation of 557.43 W/m(2), the system achieves an annual synthetic natural gas yield of 914.51 MWh/y. A high total product unit cost of 186.57 $/MWh is obtained in 2020, whereas it is predicted to decrease to 91.51 $/MWh (about 51% reduction) in a future scenario with a payback period of 4.66 years due to the significant decrement of the photovoltaic investment cost. The present work reveals the engineering realizability and economic viability of solar-to-methane and provides a competitive option for the development of solar energy.