Techno-economic evaluation and optimization of solar-driven power-to-chemical systems with thermal, electricity and product storage

Power-to-chemicals driven by solar energy for methane, methanol and gasoline are evaluated thermo-economically for three locations in Europe with high solar irradiation, and with two daily product demands and seasonal product storage. The electricity sources considered are molten-salt solar power tower technology (MSTP), photovoltaic (PV) with daily electricity storage, and the electrical grid as complementary technology to satisfy the targeted daily product demand. A bi-level optimization employs (i) mixed-integer linear programming at the lower level with heat and mass integration for optimal sizing of technologies and utilities, and (ii) genetic algorithms at the upper level for optimizing the involved technologies themselves, e.g., MSTP. Particularly, since the capital investment of MSPT contributes significantly to the levelized product cost, the optimization of the heliostat field is coupled for a potential cost reduction. The results show that (1) high local solar irradiation to ensure long annual operation hours of MSPT and PV is the most important aspect for the location selection; (2) high thermal storage capacity for ensuring long full-load operating hours of MSPT is beneficial for reducing levelized production cost; (3) PV is generally not preferred as a power source, due to the short operating hours and expensive electricity storage; (4) the plant size affects significantly the final product cost, indicating that a compact, small-scale system is far too expensive; (5) the levelized methanol and gasoline product costs per kg are lower than that of hydrogen and methane and less affected by the plant size as well as the annual power contribution of MSPT; (6) comparing with the market prices for all the three chemicals considered, solar fuels can hardly be competitive in terms of cost in the near future.