Energy, environmental and economic dynamic assessment of a solar hybrid heating network operating with a seasonal thermal energy storage serving an Italian small-scale residential district: Influence of solar and back-up technologies

In this paper a solar hybrid district heating network integrated with a seasonal borehole thermal energy storage is modelled, dynamically simulated and analyzed over a 5-year period. The system is devoted to satisfying the thermal demand for space heating and domestic hot water production of a small-scale district consisting of 6 typical Italian single-family houses, located in Naples (south of Italy). The performance of the proposed plant is investigated by analyzing 6 plant configurations differing in terms of (i) solar field and/or (ii) technology to be used as back-up system for compensating the intermittency of solar. In particular, two different configurations of solar field have been analyzed: the first one with solar thermal collectors only, the second one integrating solar thermal collectors and photovoltaic panels coupled with a battery storage; with respect to the auxiliary unit, four different alternative systems have been considered: (i) natural gas-fired boiler, (ii) natural gas-fueled internal combustion engine-based micro-cogeneration unit, (iii) natural gas-fueled reciprocating external combustion Stirling engine-based micro-cogeneration device, and (iv) wood pellet boiler. Finally, an alternative operating scheme is also proposed in order to better exploit the solar source in producing the domestic hot water. The primary energy consumption, the equivalent global carbon dioxide emissions, the operating and capital costs of the proposed configurations of the solar hybrid district network are evaluated based on the simulation results and then compared with those associated to a conventional Italian decentralized heating system in order to assess the main energy, environmental and economic benefits/drawbacks.