Techno-economic study of a zero-emission methanol based energy storage system

Within the scope of the energy transition an increasing share of intermittent renewable energy sources demand for grid balancing energy storage technologies, for which a novel zero-emission methanol based energy storage system is introduced. The objective is to establish the feasibility of this system as a grid balancing energy storage method, based on thermal efficiency and cost, at an input power of 50 MW _el and boundary conditions that are set to reflect geographically independent operation. The main components are determined to be a PEM electrolyser followed by a recirculating catalytic synthesis reactor for methanol production. Alternatives for power generation are a transcritical carbon dioxide gas turbine (tCO2-GT), a supercritical carbon dioxide gas turbine (sCO2-GT) and a combination of methanol steam reforming and PEM fuel cell (MSR-PEMFC). Modelling of the entire system with respectively tCO2-GT, sCO2-GT and MSR-PEMFC for power generation leads to a system energy efficiency of 30.1%, 26.5% and 24.1%. Levelised cost of storage is estimated to be respectively 0.24 $/kWh, 0.25 $/kWh and 0.34 $/kWh based on equipment cost estimations and factorial estimates, provisionally not taking into account the variable operational costs due to the extent of uncertainty in specifically catalyst type and degradation. Hence, based on these results the most efficient and cost effective system configuration is the tCO2-GT which can be competitive with hydrogen seasonal energy storage systems. sCO2-GT thermodynamic efficiency can be improved if cost effective solutions are found for temperature constraints. Furthermore, detailed elaboration of individual components and grid modelling of the system should lead to more accurate results and possibly increased thermodynamic performance. Concluding, when further elaborated the proposed system could be a practical solution to seasonal energy storage.