Abstract: To address surplus solar heat in solar-coal complementary systems under low-load and high-irradiance conditions, a solar-coal-storage complementary system integrating a parabolic-trough solar field, a 600 MW supercritical coal-fired unit, and molten-salt thermal energy storage was established. Two hierarchical extraction strategies, prioritizing the high- and low-pressure sides, were proposed according to extraction-steam energy grade and load-irradiance matching. Their thermodynamic, environmental, and economic performances were evaluated using an off-design hourly quasi-steady model. Based on weighted representative days for four seasons and paired results at the same load, season, and hour, the annualized net solar electricity generation of Strategy 1 at 100%, 75%, and 50% THA was 94.84, 84.26, and 73.89 GWh, respectively, 4.3%, 22.1%, and 37.1% higher than that of Strategy 2. At 50% THA, Strategy 1 achieved an equivalent annual coal saving of 28.2 kt and an operational CO₂-reduction potential of 59.4 kt, with an LCOE of 0.551 CNY/(kW·h) and a static payback period of 18.3 a. Accounting for heat-transfer temperature matching and relative area demand, Strategy 2 achieved slightly lower LCOE and a shorter payback period at full load, whereas Strategy 1 achieved lower LCOE, shorter payback periods, and higher annual net benefits at 75% and 50% THA. Within the specified unit, solar-field, TES-capacity, and hourly quasi-steady boundaries, strategy applicability is load dependent, and the high-pressure-side-priority strategy is more suitable for partial-load operation.