A 4E analysis of different Fuel Cell mCHP configurations operating with different strategies in residential applications

Abstract

This study explores the viability, assessed in terms of primary energy, exergy, CO2 emissions, and economic benefits (4 E), associated with the integration of small-scale cogeneration systems (mCHP) utilizing proton ex- change membrane fuel cells (PEMFC). The investigation is specifically oriented towards the residential sector. The model uses annual electrical and thermal demands as inputs. Parametric studies conducted through the modification of these values have been carried out. Dynamic demands are modelled using fixed consumption profiles to distribute the total annual demands. Five configurations of CHP systems based on fuel cell technology (FC-mCHP) are analysed in this work. In the first configuration FC-mCHP uses hydrogen produced by an on-site steam methane reformer. In the second configuration FC-mCHP is fed with hydrogen coming from a centralized steam methane reformer. The third configuration is similar to the second configuration but with CO2 capture in the hydrogen generator. In the fourth configuration the FC-mCHP is supplied with hydrogen produced by an on-site electrolyser. In the fifth configuration the FC-mCHP utilizes hydrogen supplied from a centralized electrolyser. Each of these five con- figurations can be combined with a heat pump system, making a total of ten options. In the FC-mCHP model, the electrical and thermal outputs are linked with the load of the system. The FC- mCHP load is set according to three operational strategies within each configuration: fulfil electricity demand, fulfil thermal demand, and fulfil both demands simultaneously. The FC-mCHP maximum electrical power serves as the sizing parameter. Additionally, the potential addition of a heat pump-based system is explored to increase thermal energy production. A conventional scenario is taken as a reference, in which electrical energy is taken from the grid, and thermal energy is supplied by a natural gas boiler. The results show that there can be primary energy savings (between 20 and 60%) as well as CO2 emissions savings, with values depending on each configuration (up to 50% for the worst ones and up to 400% for the best ones) and the average operating conditions throughout the year. However, in general, all configurations lead to economic losses, compared with the reference conventional configuration. The results also indicate that the most effective strategy involves the FC-mCHP trying to satisfy both thermal and electrical demands. When the resi- dential application is not connected to electric grid, the inclusion of a heat pump to the FC-mCHP yields relevant advantages, since additional thermal power can be generated in the heat pump, by converting part of electric power