Multi-objective capacity optimization for HPSH-PV systems: Balancing economics, PV absorption, and reservoir safety

Integrating hybrid pumped-storage hydropower (HPSH) with photovoltaic (PV) generation is an effective pathway for enhancing power system flexibility. However, strong hydro-electrical coupling in HPSH-PV systems leads to a high-dimensional planning problem, making it difficult for conventional methods to balance economics, PV absorption, and reservoir safety. Therefore, this study develops a multi-objective capacity optimization framework by introducing an empirical function to estimate PSH reservoir storage under different PSH-PV installed capacity combinations. The framework simultaneously maximizes life-cycle net present value (NPV) while minimizing PV curtailment and mean daily cumulative reservoir water-level fluctuation (RWLF), and is solved using the NSGA-III algorithm to identify Pareto-optimal solutions and reveal risk-benefit trade-offs. A case study of the Maerdang multi-energy complementary base in China demonstrates that: (1) the empirical function provides rapid and reliable estimates of PSH reservoir storage, with medium-to-high storage utilization occurring on more than 70% of days under optimal configurations; (2) a PSH-to-PV capacity ratio of approximately 1:6-1:7 achieves a balanced trade-off among economics, PV absorption, and reservoir safety; (3) stricter PV curtailment constraints require larger PSH installed capacity and lead to reduced net present value (NPV), with curtailment limits of 2% and 5% resulting in NPV losses of 1.7 billion CNY and 0.11 billion CNY, respectively; and (4) excessive transmission expansion exhibits diminishing marginal benefits and causes underutilization of PSH reservoir storage. This study provides a generic decision-support tool for preliminary planning of HPSH-PV systems under high renewable-energy penetration.