Balancing a High-Renewables Electric Grid With Hydrogen-Fuelled Combined Cycles: A Country Scale Analysis

The evolution of national energy systems towards increasingly aggressive CO2 emission reduction targets points in the long term to 80% and up to 100% CO2 emissions reduction in the power generation field, according to EU and other countries most recent policies. This will involve a massive deployment of renewable energy sources (RES), specially focusing on photovoltaic (PV) and wind power. Given the time variability of RES generation, which includes both hourly changes and a strong seasonal variation, large-scale and long-discharge-time energy storage solutions will be increasingly required to allow an adequate exchange of energy from generation to final uses. Moreover, flexible power generation solutions will be essential to cope with the large and fast ramps of power required to follow the grid residual load curves (e.g., the ‘duck curve’ given by the increasingly large PV deployment).

Hydrogen is expected to play a critical role as enabler of energy storage and sector coupling between power generation, mobility and other energy intensive sectors. At the same time, the most flexible and most efficient large-scale power generation plants, which are currently natural gas combined cycles (NGCC), may be converted and adapted to burning mixtures of natural gas and hydrogen and up to 100% hydrogen (as demonstrated recently by different manufacturers), becoming a strategic asset for future grid balancing application.

This work applies a multi-nodal model for the hourly simulation of integrated power and transport sectors at a nation scale, considering the case of Italy and aiming to study the cross effects yielded by Power-to-H2 implementation at large scale, assessing the role that can be played by gas turbine-based combined cycles in the future grid balancing.

Looking at the future energy system, which according to long-term targets should feature a dramatic surge in installed capacity of renewables and of innovative vehicles (battery electric vehicles as well as hydrogen vehicles), the article explores the capability of the power generation system to reach a 80%-100% decarbonization with reference to the electricity consumption and addresses the role of high hydrogen-fired combined cycles in the electric grid. The analysis starts from the hypothesis of keeping the current NGCC plants locations and capacities, distributing either H2-NG mixtures (e.g. at 20%vol. H₂ or higher fractions, evaluated as an hourly or daily average) or, in the long term, 100% hydrogen, through the injection  from large RES-based hydrogen production sites in the NG pipeline infrastructure. The study explores the option of repowering the NGCC sites and evaluates the effect of intra-zonal limits in power and hydrogen exchange. Moreover, results include the evaluation of the required hydrogen storage size, distributed at regional scale or in correspondence of the power plant sites.