The potential of hydrogen enriched natural gas deriving from power-to-gas option in building energy retrofitting

This paper deals with the role of Hydrogen enriched Natural Gas (H2NG) in Hybrid Energy Systems for energy refurbishment purposes. In detail, three different plant layout options were investigated. A photovoltaics (PV) array and two-stage electric heat pump (EHP), a hybrid photovoltaic thermal solar collectors combined to gas heat pump (GHP) fuelled with H2NG, and a CHP fuelled with H2NG connected to a two-stage EHP were compared. The required receiving surfaces of PV array were estimated for three different direct normal irradiation (DNI) values in Italy in order to assess how the available roof surface affects the layout choice. A sensitivity analysis was carried out with varying the building power to heat ratio (PTHR) and the hydrogen volumetric fraction in the H2NG mixtures to assess the primary energy consumption (PEC) and renewable energy fraction. When feasible, the PV + EHP shows the best performance in terms of PEC with a solar energy share equal to 65%. In other cases, the PV/T + GHP fuelled with H2NG @30%vol. can be suitable for PTHR higher than 0.2 approximately. Furthermore, the third layout CHP + EHP is not competitive with the other solutions but, it is the best option where no roof surfaces are available for PV or PV/T installation.