Impact of solar field design and back-up technology on dynamic performance of a solar hybrid heating network integrated with a seasonal borehole thermal energy storage serving a small-scale residential district including plug-in electric vehicles

A solar hybrid district heating network integrated with a seasonal borehole thermal energy storage is dynamically simulated and analyzed over a 5-year period. The system is devoted to satisfying the space heating and domestic hot water requirements of a small-scale district consisting of 6 typical Italian single-family houses, located in Naples, with home charging of 6 plug-in electric vehicles. Eight different plant schemes differing in terms of solar field configuration and/or back-up system used for compensating the intermittency of solar source are investigated. Two different configurations of solar field are analyzed: the first one with solar thermal collectors only and the second one integrating solar thermal collectors and photovoltaic panels coupled with a battery storage; three different alternative auxiliary units are considered: natural gas-fired boiler, natural gas-fueled internal combustion engine-based micro-cogeneration unit and wood pellet boiler. An additional operating scheme is also proposed to better exploit the solar energy for domestic hot water production. The primary energy consumption, the carbon dioxide emissions and the operating costs of the proposed plant configurations are evaluated based on simulation results and then compared with those associated to a conventional decentralized heating system in order to assess the main energy, environmental and economic benefits/drawbacks.