Green hydrogen for energy storage and natural gas system decarbonization: An Italian case study

The increase of the electricity production from non-programmable and intermittent Renewable Energy Sources (RESs) generates criticalities in the balance between the energy supply and demand, requiring significant energy storage capabilities for the next future. The exploitation of the available NG Transmission Network (NGTN) by implementing the Power to Gas (PtG) technology is particularly promising since it allows a massive energy storage capability and the decarbonization of the NGTN by green hydrogen injection into the grid with growing percentages up to 100%. The objective of this work is to analyse the actual feasibility of distributed green hydrogen generation and its injection into the national NGTN. A mathematical model has been developed to assess the dynamic operation of a PtH2 integrated system to produce green hydrogen using photovoltaic-powered electrolysers and to inject it into the NGTN upstream of a Regulating and Measuring Station (RMS) located in central Italy. Three different surface sizes are considered for the installation of PV panels (100 m2, 300 m2 and 500 m2) and the optimal hydrogen accumulation size has been calculated in order to ensure the uniformity of the supplied mixture throughout the year. Obtained results show that employing the optimal accumulation size, hydrogen percentage in the NG-H2 mixture ranges between 0% and 0.90% by volume. In the best-case scenario (i.e., when considering a surface area of 500 m2), the cost of hydrogen production is 5.10 EUR/kg H2 and the PtH2 plant allows to save 32.348 tonnes of CO2 emissions every year.