The production of hydrogen as both chemical feed and energy carrier using low-carbon technologies is one of the solutions to reach net-zero emissions. This paper, firstly, reviews the publications on the life-cycle assessment of photovoltaic (PV)-based hydrogen production focused on the carbon footprint. Secondly, it updates the global warming potential (GWP) values of this H₂ production process considering the state-of-the-art PV panels for installation in Italy. In the literature, H₂ produced in Europe and the rest of the world results in a mean GWP equal to 4.83 and 3.82 kg CO₂ eq./kg H₂, respectively, in which PV systems contribute the highest share. The average efficiency of PV panels assumed in the literature is lower than the current PV modules. Updating the supply chain, efficiency, and manufacturing energy and material flows of PV modules can decrease the GWP value of the H₂ produced by nearly 60% (1.75 kg CO₂ eq./kg H₂, with use of alkaline electrolyzer) in the Italian context, which can be further reduced with advancements in PV panels or electrolysis efficiency. The study proves that advancement in the PV industry and additional savings in the electrolyzer’s electrical demand can further decrease the carbon footprint of PV-based H₂.

Gas absorption heat pumps represent an alternative to condensing boilers for space heating and domestic hot water production in existing buildings. In particular, they enable fuel saving and the exploitation of renewable energy even in heating systems based on radiators, which require high supply temperature. However, in order to provide useful indications to policymakers, manufacturers, and system designers, a fair comparison of two technologies has to be based, besides the energy consumption and the direct CO2 eq emissions, also the environmental impact over the entire life cycle. Thus, in this paper, the environmental profiles of a condensing boiler and a gas driven absorption heat pump are compared as competing technologies to provide space heating and domestic hot water in old (constructed before 1980) and not refurbished buildings. The assessment was carried out for three buildings located in three representative European climates, using 1 kWh of thermal energy produced by the two systems as the functional unit. The Ecoinvent 3.6 was used as background database and the EF 3.0 normalization as weighting set method. Uncertainty and sensitivity analysis were also included. The results show that the use phase contributes for more than 97% of the total impact for both the energy systems in the three climate zones. Despite the higher electricity consumption, the gas driven absorption heat pump offered a lower environmental profile compared with the condensing boiler, mainly because of the lower amount of natural gas needed in the use phase. In particular, an average reduction of 27% was found for CO2 eq, 25% for fossil resource consumption, and 22% for weighting results.