A MILP model for the design of multi-energy systems with long-term energy storage

Optimal design and operation of multi-energy systems involving seasonal energy storage are often hindered by the complexity of the optimization problem. Indeed, the description of seasonal cycles requires a year-long time horizon, while the system operation calls for an hour resolution; this turns into a large number of decision variables, especially binaries. This work presents a novel mixed integer linear program methodology that allows considering a year time horizon with hour resolution whilst significantly reducing the complexity of the optimization problem. The validity of the proposed technique is tested by considering a simple system that can be solved in a reasonable computational time without resorting to design days. Findings show that the proposed approach provides results in good agreement with the full-size optimization, allowing to correctly size the energy storage and operate the system with a long-term policy, while significantly simplifying the optimization problem.