This study proposes a floating photovoltaic - pumped hydro energy storage system integrated with a water electrolyzer for combined power and hydrogen generation. Compared to solutions without electrolyzers, this integrated system is able to further mitigate the non-programmable photovoltaic generation and simultaneously decarbonize hard-to-abate sectors. The performance of the integrated system is herein studied on daily, monthly, and yearly bases using a mathematical model with a 1-hour time resolution for a real case represented by a pumped hydroelectric energy storage system in Sardinia. The study considers integrating the existing system with a 11 MW floating photovoltaic system and a 4 MW PEM electrolyzer, appropriately sized to achieve a hydrogen production target of 100 tonnes per year and a photovoltaic self-consumption not below 95%. The power used for pumping water and producing hydrogen is 100% renewable, as it is supplied solely by the floating photovoltaic plant, and the electricity is fed in the grid at night, aiming to increase the share of renewables in the nighttime energy mix of the Sardinia region. Results show that the integration provides significant benefits to the grid, with 8.5 GWh/year of nighttime inertial feed-ins. Moreover, since the integrated plant is characterized by annual self-consumption values of photovoltaic generation around 97% and monthly values never below 93%, the negative impact caused by its non-programmable feed-ins on the grid is minimal. Hydrogen production, capable of replacing approximately 0.1% of the current yearly fossil fuel-based thermal demand of the regional industrial sector, exhibits strong seasonality, with daily production averaging 65 kg/day during winter months and over 7 times more (465 kg/day) during summer months, suggesting the opportunity for a seasonal storage.
