Electrolytic hydrogen in a large-scale decarbonized grid with energy reservoirs: An assessment of carbon intensity and integrity

Electrolytic hydrogen (e-H2) is under scrutiny worldwide to become a primary vector for decarbonization. Production of e-H2 in Brazil is a unique case study because of the singularities of the electricity grid, which has a continental scale, is highly decarbonized (93 % renewables in 2023), and incorporates substantial energy storage (210 TWh) and dispatch flexibility (circa 50 GW) in hydro reservoirs. In this distinctive context, this study evaluates the carbon intensity (quantified through a cradle-to-gate life cycle assessment) and the requirements to ensure the carbon integrity of grid-connected e-H2 production. The study gathers inventories of solar and wind energy systems and alkaline electrolyzers. It also presents georeferenced modeling of carbon emission factors for solar and wind energy, along with hourly simulations of grid-connected e-H2 production. Carbon intensities within 2.9–4.0 kgCO2eq kgH2−1 are calculated with solar energy and as low as 1.0 kgCO2eq kgH2−1 with wind energy. Energy sourcing from the best wind sites leads to the lowest carbon intensities, even if adding the impacts of long-distance (2000 km) transmission. Simulation of e-H2 production with wind energy assisted by energy storage in hydro reservoirs shows that electrolysis at a high capacity factor (≈90 %) is possible without impacting grid emissions and reservoir functionality. This result demonstrates that the requirement of hourly matching between additional energy generation and consumption is unsound for e-H2 production in a grid rich in renewables. Instead, the temporality of electrolysis must consider the permissible temporal unmatching enabled by the grid-based energy storage and the complementarity between the legacy and the additional renewable sources.