Innovative energy systems and processes based on hydrogen from RES and its derivatives in the energy transition process

This thesis investigates the integration of green hydrogen and ammonia production in renewable energy-powered energy systems, as a decarbonization pathway in the energy sector. Climate change mitigation and the transition to carbon-free energy systems are challenged by the inherent intermittency of renewable sources, which affects grid stability and can lead to energy curtailment. By converting surplus renewable electricity into chemical energy carriers such as hydrogen and ammonia, it is possible to enhance system flexibility, support grid services, and provide carbon-free fuels for hard-to-abate sectors and power generation. In this research, mathematical modeling is used to develop, optimize and analyze integrated energy systems based on variable renewable energy generation, water electrolysis, energy storage and ammonia production. Two main approaches to system integration are examined: the first combines green hydrogen production with mechanical energy storage (via compressed air energy storage or pumped hydro energy storage) to provide grid balancing and minimize curtailment, while the second analyzes a fully dedicated green ammonia production plant. The performance of each configuration is assessed to identify the optimal system design and operational strategies. With reference to green hydrogen and mechanical storage integrated solutions, two different configurations are analyzed in detail. In the first configuration, a photovoltaic plant is integrated with a compressed air energy storage system fueled by green hydrogen produced on-site. This approach achieves a round-trip efficiency of approximately 62%, a reduction of photovoltaic curtailment to 4%, while delivering grid flexibility services using carbon-free fuel. On the other hand, the second system integrates hydrogen production in a floating photovoltaic-powered pumped hydro energy storage plant, using surplus energy to maximize self-consumption utilizing 99.2% of renewable energy generation. Finally, a green ammonia production system is optimized using a mixed integer linear programming approach, allowing for the simultaneous optimization of component size and operation scheduling to minimize production costs. The analysis achieves temporal decoupling of yearly ammonia production from fluctuating photovoltaic input with minimal intermediate storage, with a system efficiency of 45.5% and a levelized cost of ammonia of 995 €/ton.