Stochastic optimal design and operation of floating solar and hydropower system for integrated water-energy-food-ecosystem planning

• A two-stage stochastic model optimises hybrid FPV-PSH under future uncertainty. • Progressive objectives reflect energy, water, food, and ecosystem trade-offs. • Irrigation and evaporation impacts are jointly optimised through system design. • Hybrid FPV-PSH improves dispatch stability and enhances energy self-consumption. • Ecosystem valuation drives higher FPV adoption and lower grid dependency. This study presents a high-resolution, two-stage stochastic optimisation framework for the configuration and operation of a hybrid floating photovoltaic (FPV) and pumped-storage hydropower (PSH) system. The model captures interdependencies among sectors through progressive optimisation perspectives, including energy-only (E), water-energy (WE), water-energy-food (WEF), and water-energy-food-ecosystem (WEFE), each expanding the system boundary and revealing cross-sectoral trade-offs. Methodological innovations include endogenising evaporation losses within the optimisation dynamically linked to FPV deployment, optimising agricultural area as decision variable, and embedding ecosystem values such as avoided CO₂ emissions, land-use savings, and biodiversity costs directly into the optimisation objective. Uncertainty is addressed through Monte Carlo-based hourly scenario generation, while a layered objective function systematically expands system integration. Results show that broader perspectives substantially shift optimal FPV capacity and hydropower dispatch, while enhancing the economic viability of hybrid configurations. In the WE case, evaporation savings drive larger FPV deployment and increase PSH output by over 11 % on average, while integration of irrigation constraints in the WEF case highlights seasonal trade-offs and optimal irrigation areas. Incorporating ecosystem values in the WEFE case leads to maximum FPV deployment across wide cost ranges, with hydropower ramp rate reduced by 16.4 %. CO₂-price sensitivity further confirms that higher carbon valuation widens the feasible deployment space, increasing FPV power by 15.84 % on average. The framework advances WEFE-integrated planning by linking high-resolution sectoral interactions with ecosystem valuation, offering practical insights for resource-efficient, low-carbon systems that balance competing demands under uncertainty and support long-term sustainability goals.