Comparing operational flexibility and performance of pumped hydro energy storage systems

This work compares the operational flexibility, energy capacity and efficiency of four standard pumped hydro storage configurations in a 100 MW and 10 h system. The analysis applies two technology options for enhanced flexibility to these configurations: variable-speed operation and hydraulic short circuit (HSC). To simulate system behaviour, a detailed physical model is developed that captures off-design performance, dynamic head variation, and is validated with original equipment manufacturer data. Variable speed enables an operating window around the pump's nominal charging power with limited efficiency penalties, increasing operating-range coverage from 31.5% to 50.5% in a single binary set. HSC operation enables flexibility in deep part-load charging; the operating-range coverage rises from 33.8% to 55.1% in a single ternary set and to 89% in two ternary sets compared with 42.3% without HSC. HSC system efficiency is much lower due to counter-acting power flows and can reach zero even while the individual component efficiencies remain high. Ragone plot analysis is used to quantify the energy capacity at different power levels and shows that high-power HSC charging is prematurely terminated by turbine flow constraints. Advanced flexibility combinations of variable speed and HSC demonstrate potential since their characteristics complement each other, increasing the operating range from 42.2% to 71.8% in the single binary machine set configuration.