Design and operation optimization of renewable energy systems including short and long term storage for residential applications

This work studies the optimal integration of short- and long-term energy storage in a renewable-based residential multi-energy system serving five apartments in Padova. The objective of the work is to compare the roles of the different energy storage systems like electrical energy storage (EES), thermal energy storage (TES), and hydrogen storage under various demand cases, grid scenarios, and operational-emission conditions. The system includes photovoltaic generation, a heat pump, EES, TES, an electrolyzer, hydrogen storage, a fuel-cell CHP unit, and a hydrogen boiler. A Mixed-Integer Linear Programming model was developed in Python and solved with Gurobi for the optimization of the component sizes and hourly operation while minimizing total annualized cost. Eight seasonal weekday/weekend representative periods were used, with a linked 365-day formulation to keep long-term hydrogen-storage chronology. Five storage configurations were evaluated for simultaneous-load and shifted-load demand scenarios under grid-connected and off-grid operation. An additional emission-constrained analysis was performed at ε = 0.25, corresponding to a 75% reduction in modeled operational CO2 emissions relative to the reference system. For grid-connected operation,PV, heat pump, and TES dominated for the low cost solutions with annual costs of about 4.1–4.6 kEUR/year. In off-grid operation, the Hybrid and EES+TES configurations showed the lowest costs, approximately 7.9–8.35 kEUR/year, requiring about 30 kWp of PV and 30–32 kWh of battery capacity. Hydrogen-based off-grid systems are considerably more expensive, reaching approximately 18–19 kEUR/year, while the hydrogen-only simultaneous-load case is infeasible. Under the stricter emission constraint, configurations with EES met the required reduction with only about a 4–6% cost increase, whereas hydrogen-based alternatives experienced significantly larger increases. Overall, the results show that TES is effective for short-term thermal flexibility, EES is the most economical short-term option for electrical balancing, and hydrogen becomes relevant mainly when longer-duration storage is required or alternative options are limited.