Multi-objective optimization of solar photovoltaic and solar thermal collectors for industrial rooftop applications

Solar-derived industrial process heat could be harvested from the rooftops of factories around the world, but stakeholders must make some choices about which solar technologies to install (of those available on the market) to find the ‘best’ fit to local conditions. For industrial process heat, solar thermal (ST) collectors can generate medium temperature thermal energy directly, but solar photovoltaics (PV) can also be used—indirectly—to generate the same thermodynamic quality via resistance heating or a heat pump. To systematically investigate this solar dilemma, options ranging from 100% PV to 100% ST were considered in this study in the context of several objective functions to determine the ‘best’ technological mix. The objectives functions—economic (levelized cost of energy), technical (overall performance) and environmental (embodied emissions)—were applied individually and collectively, as multi-objective optimizations, to gain insights into how each might impact the optimum mix of solar technologies. A sensitivity analysis was also carried out to explore the impact of our assumptions (design and costs) on the optimal system design. The results reveal the optimum solar mix between the various objectives varies significantly in the 12 characteristics global locations considered in this study and that the capacity factor varies between (8–45)%. Generally, it was found that a mix of technologies (not solely PV or ST) in a side-by-side configuration improves performance, the levelized cost of energy, and the environmental payback time (by up to 35%, 9.8%, 16%, respectively, when compared to ST alone, and by up to 21%, 16.1%, 11.8%, respectively, when compared to PV alone). Overall, the approach and the results of this study can be used as a guideline for architects, engineers, and decision makers to help decide the best mix of solar technologies for industrial process heat applications based on their objective(s).