Optimization of the power output scheduling of a renewables-based hybrid power station using MILP approach: The case of Tilos island

Hybrid energy systems comprising renewables (mainly wind and solar) and storage systems are increasingly welcome to serve small communities or areas, such as small islands. In particular, the present study deals with the hybrid power station of Tilos, a little island located in the Greek Dodecanese, which includes a 800 kW wind turbine, a 160kWp PV field, and a 2.88 MWh NaNiCl2 battery; the system is also connected to the Kos-Kalymnos electrical network via a submarine cable. Currently, it is used to export its whole energy production under the management of the Greek company Eunice Energy Group. The agreement with the grid regulator is conceived to involve a remuneration for the energy output in three power levels (0 kW, 200 kW, 400 kW), with hourly dispatch provided the day before. Economic penalties will be applied in the near future for failure to respect power levels, whether in the form of excess or deficiency. This must be done in accordance with the available power to avoid surpluses or deficits, as well as excessive curtailment of renewable energy. In this work, a way to optimize energy fluxes of the island is proposed to better exploit the potential revenue, without excessively resorting to curtailments. The optimizations are performed in a Python environment through the "Gurobi" optimization solver, which is based on Mixed Integer Linear Programming (MILP). Scheduling emerges as a result of a rolling horizon approach. The new scheduling method reveals that there is potential for an increase in exported energy by 87.1% and potentially doubles the earnings over the current operation. Furthermore, novel scenarios are proposed to explore how different agreements with the grid operator would shift the optimal solution. Compared to an ideal optimized control under the current restrictions, a scenario that introduces the possibility of shutting down the wind turbine may increase the annual earnings by 10%, while a scenario that introduces a higher power band has the potential to increase annual earnings by 29.1%.