Modeling and techno-economic analysis of the integration of a FC-based micro-CHP system for residential application with a heat pump

This work aims to analyse the techno-economic performance of an integrated system for a residential CHP (Combined Heat and Power) application, based on the integration of a Fuel Cell (FC) micro-cogeneration device coupled with an Heat Pump (HP). The main components of the system are: the Fuel Cell unit, the Heat Pump and the thermal storage – required to cover the thermal peaks, mainly due to the domestic hot water demand. The analysis will be focused on the most diffused FC technologies for residential applications: a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) and a high temperature Solid Oxide Fuel Cell (SOFC). FC-based cogeneration systems usually produce an electric power surplus respect to the thermal production, because of their high electrical efficiency. Currently, however, the households heating load exceeds significantly the electricity requirements, thus making difficult the sizing of a FC system for a single family house without including large electrical and thermal storages or high grid/boiler integration. The combination of a Fuel Cell and an Heat Pump has been found to be an optimal solution to manage this problematic while achieving a reduction in the primary energy consumption and avoiding energy overproduction. In the proposed scenario the heat is exploited by feeding both the domestic hot water and a low-temperature radiant floor heating system operating between 35 °C and 45 °C. An energy and economic analysis has been performed to understand and to evaluate the plant feasibility. Results have pointed out that the best economic choice, with the current energy tariff scenario, is related to a small size FC-based CHP system able to produce enough electrical power to feed the HP plus a low electrical consumption (<1 kW electrical size), which corresponds to the base electrical household consumption (the electrical power which is near-always requested by the house). The electrical load is in fact deeply changing during the day (with one-minute variable peaks) and with a higher electrical production from the FC, most of the electrical power would be sold to the grid without no energy advantages. The best PEMFC configuration was able to reach a total efficiency of 75%: if compared to the case with separated energy generation (electricity from the grid and heat from a boiler) the saving is estimated in three years of payback for the current scenario (2015). With the SOFC system, thanks to its higher total efficiency equal to 81%, the primary energy consumption was reduced (−30% respect to PEMFC) with a consequent reduction in the operating costs. However, from an economic point of view, the payback still results extended because of its not competitive investment cost.