Hydrogen from renewables: Is it always green? The Italian scenario

Abstract

Green hydrogen production through water electrolysis is recognized as a pillar for the energy transition toward a complete decarbonized economy. The aim of this study is to investigate the potentiality of electrolytic hydrogen (suggesting stricter definitions of green and yellow hydrogen) from grid electricity in Italy and its impact on the reduction of renewable power curtailment and CO2 emissions for the scenarios with increased photovoltaic and wind capacities up to 5 times the 2019 ones. Several electrolysis overall capacities, defined on the basis of the curtailment duration curve, were analyzed. Results showed that hydrogen production based only on the curtailed energy (green hydrogen) leads to a very low utilization factor of the electrolyzers (no more than 22% in the highest penetration scenario) and consequent high specific hydrogen production costs. The annual production of green hydrogen is small in all analyzed cases and far from the stated Italian and European targets. A minimum electrolysis utilization factor should be imposed to reduce the hydrogen production cost by using additional natural gas-generated electricity (yellow hydrogen). However, in this way, specific emissions increase and become even greater than those of the most diffuse steam methane reforming process when the utilization factor imposed doubles the green hydrogen one. The sensitivity analysis showed the influence of the capital cost of the electrolyzers and of the electricity cost for additional non-curtailed energy on the levelized cost of hydrogen.