Storage of excess energy from non-programmable renewable sources in existing natural gas infrastructure, using hydrogen produced by electrolysis as the energy carrier, is an option of great interest at both the national and the international level and aims to the gradual replacement of fossil natural gas with renewable gas. However, the chemical-physical properties of hydrogen are profoundly different from those of methane and other hydrocarbons that make up the mixture known as ‘natural gas’ and the opportunity to inject greater fractions of it into the grid must be carefully evaluated. This report presents an overview of the possible criticalities that arise from this, for both gas infrastructures and end users. Examining the literature has allowed us to identify some issues that require further investigation and will be the subject of further studies (including experimental ones) by RSE.

At the level of grid infrastructure, experts are reluctant to define a maximum allowable limit for hydrogen in gas that is temporarily injected and stored underground; this is because of the numerous biotic and abiotic processes that can take place underground. This report describes and analyses, in particular, the microbiological processes that can impact, even negatively, on the underground storage of natural gas and hydrogen mixtures. At the user level, regulatory and technical barriers were identified for gas-fuelled vehicles and for the power (co)generation fleet. Attention focused on this last aspect in view of the experimentation, at RSE, of small gas devices for medium-long periods, also using natural gas mixtures with variable hydrogen content, for the monitoring their energy and environmental performance.

Contacts have been initiated with a cogeneration engine manufacturer and suppliers of the equipment needed to set up the test station. The experimentation aims to promote the development of a new generation of devices suitable for functioning correctly even with increasing fractions of hydrogen in the network. Finally, the actions carried out within the numerous technical tables in which RSE participates are described, in support of Institutions, Authorities and Regulatory Bodies, in view of an ever-increasing diffusion of the so-called renewable gases in Italy.