Perspective of the role of hydrogen in the 21st century energy transition

Hydrogen is gaining momentum in the current global energy transition framework. In fact a great and widespread enthusiasm is growing up towards it, as indicated by the current worldwide economic and political strategies, which endorse the carbon neutrality by 2030 and a fast transition to clean energy. Green hydrogen has the potential to create a virtuous cycle for the future renewables-based electricity grids, as it can provide the much-needed flexibility to power systems, acting as a buffer to non-dispatchable renewable generation. Indeed, the excess energy, provided by conventional and renewable power plants, can be stored as hydrogen and then employed to produce electricity (fuel cells or power systems), heat (combustion) or both (co-generation), abating drastically the greenhouse gas production. In this scenario, it is important to understand what benefits could derive from the use of hydrogen. For this reason, the present work not only aims at reviewing the recent updates on hydrogen economy (in terms of the main advantages and drawbacks) but also focuses on determining the impact that this hydrogen may have in various sectors (transport, industry and power generation). Different assessments have been carried out showing how hydrogen can effectively contribute to the carbon neutrality goal. This work points out that hydrogen can be really sustainable if produced via electrolysis powered by renewable energies. Furthermore, for the mobility, the use of fuel cells currently turns out to be less efficient than the adoption of Li-ion batteries, but at the same time far less polluting (CO2,eq) and labor intensive. Finally, a near-term solution to contrast the power generation carbon footprint, namely the blending of fossil fuels with hydrogen, has been investigated. Thus, a real Combined Cycle Gas Turbine power plant has been selected as a case study, in order to assess the impact of the hydrogen employment in terms of power output and emissions with respect to the current status of the plant fueled with 100% natural gas. As a result, using a mixture with 70% CH4 and 30% H2 a remarkable reduction of CO2 can be achieved (0.28 Mt CO2/year ).