Capacity planning of large-scale wind-photovoltaic-pumped hydro storage energy bases under sending–receiving-end spatiotemporal mismatches

Long-distance transmission of wind and solar power often exposes a mismatch between renewable availability at the sending end and demand requirements at the receiving end. This study examines how such spatiotemporal differences influence capacity planning for a large wind-photovoltaic-pumped hydro storage (WP-PV-PHS) energy base connected to an external load center via an ultra-high-voltage direct current (UHVDC) line. A two-layer planning framework is used, combining capacity optimization with an 8,760h operational simulation. Three operating conditions are assessed. In the free-transmission (FT) case, exported power follows the natural variability of WP-PV resources, constrained only by UHVDC limits and PHS operation. When an agreed transmission curve (ATC) case must be followed, the temporal misalignment between supply and demand becomes evident: exported energy drops, curtailment increases, and periods of insufficient supply emerge. Introducing a small gas turbine (GT) in the ATC-GT case mainly supports hours in which PHS alone cannot restore the required output, improving the system’s ability to meet the transmission target. Results indicate that enforcing the ATC reduces annual exported electricity by roughly 15-20% and increases curtailment by more than 10%. Adding 1 GW of gas turbine capacity markedly improves the supply guarantee with limited cost impact. The analysis shows that planning large WP-PV-PHS energy bases requires explicit consideration of both renewable output patterns and receiving-end demand constraints, especially when UHVDC systems impose strict operational limits.