6. Turbine pumps

In today's large-scale electricity grids, thermal generation (of conventional or nuclear origin) is taking on an increasingly important role compared to hydro generation; however, it cannot easily provide the modulation required to keep pace with large-scale, sudden variations in consumption (figure 30 ). Hence the idea of using surplus off-peak electricity to store potential energy by pumping water into reservoirs at altitude, and then releasing it at peak times. This is the function of pump turbines, which can easily cope with rapid load variations.