Medium- and long-term optimal operation of a hybrid energy system enhanced by cascade hydropower energy storage system

To address the grid connection challenges derived from the high penetration of intermittent new energy sources, some generation companies are trying to use existing cascade hydropower stations to develop "large-scale cascade hydropower energy storage systems" (LCHES). They intend to combine the LCHES with new energy power to become a new type of hybrid power system (the LCHES-WP hybrid power system). For such an emerging hybrid power system, performance in the medium- and long-term operation is more worthy of attention. Therefore, we propose "monthly LCHES-WP operation strategy" and "short-term dispatch strategy for LCHES" to constrain the operation of the LCHES-WP hybrid power system. On this basis, a multiple time-scales nested optimizing model is presented to estimate the performance in the medium- and long-term operation. A case study in the Yellow River Basin in China was presented based on the baseline scenario (1800 MW of hydroturbine, 1200 MW of pump, 2000 MW of new energy, and 0.24 billion m(3) of regulating storage capacity). It reveals that (1) the LCHES-WP hybrid power system can achieve a consistent output process every day during a month with low energy curtailment and low energy supply shortage, which indicates that it can meet satisfactory performance in medium to long-term operation. (2) it will significantly increase energy curtailment (controlling the energy supply shortage is as low as the baseline scenario) without the pumping system or sufficient regulating storage capacity. (3) based on sensitivity analysis, it is indicated that the capacity of new energy can further improve to 5000 similar to 6000 MW. The simulation framework and the result provided in this paper can be referred to by the same research.