Hydropower Information >> General Information >> Pumped Storage Database A notable feature of pumped storage is its excellent maneuverability in operation. It is usual to design pumped storage systems with high head and a short a distance between the two reservoirs. (A high head reduces the size of the reservoirs required to meet the daily loading cycle-usually, only small reservoirs are required). If these criteria are optimized, it is possible to start up from zero power to full power within several minutes. It is quite usual for grid system operators to hold pumped storage stations in such a standby mode, ready to cover any peaks of electricity demand associated with rush-hour peaks, or breaks in TV programmes. However, it is usually possible to improve on this loading performance by operating the pumped storage units spinning-in-air-either spin-pump or spin-generate. In these reserve modes, pumped storage units use less than 1 % of their rated power, but by opening water valves they can be changed to a pump or generate mode in perhaps less than 10 S (depending on particular plant performance). Furthermore, dependent on the characteristics of the hydraulic design of a pumped storage station, it may be possible to swing the power-output widely within several seconds; such plants may be operated dynamically as part-load-reserve machines. Then pumped storage plant works as a reserve power generator to cope with any unexpected power demand or generation-loss fluctuation on the supply grid. Since operation of pumped-storage plant is usually completely automated, all of these changes in mode and loading can be initiated to automatically respond to rises and falls in supply frequency with no intervention or monitoring by the grid system operator. In such manner, pumped storage contributes to maintain the quality of the electric power such as its frequency and voltage, and to improve the reliability of the system. Figure 3 shows an illustration of a pumped storage plant operating in these modes. But pumped storage plants are net users of electrical energy. The generation and pumping cycles are usually only 90 % efficient, and energy is also lost to hydrological friction. Typically, the total scheme may only be 75 % efficient across the energy storage cycle. A hasty analysis might conclude, therefore, that such plants are harmful to the environment because of this energy waste, and consequent dump of gaseous emissions. A more detailed analysis can reveal this is not the case (dependent on the generation mix of the supply grid, the stability of the grid, and other factors). It may be that a reduction in emissions results as pumped storage displaces older plant from the day-time peaks, absorbs clean nuclear energy at night, and replaces part-loaded, inefficient steam plant from standby and reserve duties. From this brief description it can be seen that pumped storage stations can adopt a number of roles within the operation of a electrical supply grid, and can perform some of these roles concurrently. It is common for the operation of pumped storage plant to vary over time as they are asked to adapt to changing market conditions. Because of the flexibility of the plant, they are usually well placed to exploit a varying commercial environment. The environmental impact of pumped storage stations is usually much less than that of a conventional hydropower station since the required water storage is usually much smaller. The need for a pump-priming head usually positions the pump-turbine below the level of the lower reservoir, often underground. The typical design life of a pumped storage station is 80-100 years. As a result, the environmental impact of pumped storage construction and operation very low. This brief introduction allows us to summarize the principle areas of pumped storage benefits: improved energy regulation and operation of the supply grid. delivers ancillary services to the supply grid, such as standby and reserve duties, black-station start, frequency control, and flexible reactive loading. creates environmental benefits such as reduced gaseous emissions and has little environmental impact during its operation. allows flexible and rewarding commercial operations across a variety of electrical power supply scenarios. The evolution of Pumped Storage Technology << Back