H2NG use implications in Hybrid Energy Systems for Building Refurbishment in Future National PtG Scenarios

In order to comply to the ambitious targets set by the recent European Hydrogen Strategy, Member States will strongly encourage the development and deployment of Power-to-Gas (PtG) technologies. A significant fraction of produced green hydrogen will be injected into the existing natural gas networks, and the end-users will be served by Hydrogen enriched Natural Gas blends (H2NG). In such a way, the NG pipelines will be used as a widespread hydrogen storage medium and, at the same time, the hydrogen blending will contribute to decarbonise non-electrical final energy consumptions. The H2NG use in the civil sector will increase the primary fossil energy savings which can be accomplished by the use of efficient gas-driven plants. In detail, in building refurbishment, the application of gas-based hybrid systems will be more effective in terms of energy savings and avoided emissions. However, if the levelized cost of hydrogen (LCOH) by electrolysis does not decrease, this will affect the cost-effectiveness of this systems compared with electric heat pumps (HP). The aim of this paper is to analyse the H2NG effects on technical, economic and environmental parameters of hybrid energy systems for building refurbishment. The building thermal load analysis has been carried out by a certified software simulation tool (Termolog) able to perform dynamic analysis of heating and cooling loads, according to EN/ISO 52016. The electrical load has been evaluated by combining the bill analysis and the load profiles reconstruction method for non-residential building, proposed by Lindberg et al. A reference scenario, consisting of separate generation by natural gas boiler and electricity from national grid has been analysed. Therefore, 3 hybrid energy systems have been proposed for the existing plants replacement. The first configuration envisages a photovoltaic (PV) array and an electric heat pump, which has been identified as the best available technology (BAT). Then, a CCHP (Combined Cooling Heat and Power) system, composed by an internal combustion engine, together with an absorption chiller, has been coupled to a backup boiler, electrical chiller, and to a PV plant (scenario C). Thereafter, a further hybrid systems consisting of CHP and HP have been assessed (scenario D). The PV plant has been sized using all the available surface, since it allows a peak power much lower than the average power of building electrical load. The fuel supply has been simulated by varying the H2 volumetric fraction in the H2NG, in a range between 0-20%vol. All scenarios have been dynamically modelled in Simulink/MATLAB and simulated by hourly step over a whole year. For each hybrid system configuration and for each H2NG scenario, the Primary Fossil Energy Consumption (PFEC), the share of renewable energy in the building (%RES), the CO2 equivalent emissions, the Net Present Value (NPV) of the investment, the internal rate of return (IRR), the Profitability Index (PI) and the Carbon Avoidance Cost (CAC) have been calculated. The PV+HP system is the best configuration in terms of energy and environmental performance, despite the small surface available for the PV array. The hydrogen in the gas network allows to get to higher building decarbonisation levels; moreover, when the H2 fraction is equal to 20% vol., scenario D shows CO2eq emissions below those associated to the BAT. Assuming a LCOH value equal to 4 €/kgH2, as the share of hydrogen in the network increases, the financial indicators of the investment lessen. However, the scenario C, even for H2 fractions equal to 20% vol., shows financial indicators higher than PV+HP scenario. Since all the scenarios are cost-effective over the relevant time horizon, in each analysed configuration the CAC has a negative value. The CAC value is better for hybrid scenarios; the hydrogen worsens this indicator, however, even with H2 fraction equal to 20% vol., it results better than PV+HP scenario. The H2NG blend use will allow greater primary energy savings and avoided emissions, but these benefits will probably be offset by a lower economic competitiveness. Further research developments, in order to draw up a full paper, concern a sensitivity analysis on the building Power-to-Heat Ratio and LCOH.