Comparative modelling and scenario analysis of sector-coupled island energy system optimisations

Dispatch optimisations of an off-grid island energy system were carried out. These optimisations compared a linear and piecewise linear efficiency modelling approaches for sector couplers, different Dunkelfkaute weather scenarios; and different horizon lengths over one year with an hourly resolution. Solar and wind power are complemented by battery and hydrogen storages, along with sector couplers: electrolyser, fuel cell, gas turbine and steam boiler to meet electricity and high-temperature heat loads. The unit dispatch optimisations were conducted in PyPSA. The piecewise linear model showed a concentration of the operation points at maximum efficiency for the electrolyser, which can be operated more flexibly than the other components. When modelled with constant efficiency, the gas turbine showed a significantly higher electricity output. The fuel cell and the steam boiler did not show significant differences, between the two modelling approaches. The relatively minor influence of horizon length underscored the importance of thorough pre-optimisation strategies, particularly in anticipating and managing Dunkelflaute events, where long-term foresight is crucial for system resilience. A four-week Dunkelflaute showed that the capacity of the EL in conjunction with the availability of electricity from RE in the period before the Dunkelflaute was the limiting factor for bridging the Dunkelflaute.