If the renewable electricity is delivered with large fluctuations of the generated electricity, the availability of quickly responding power plants becomes increasingly important to avoid supply bottlenecks of the supply. Storage hydropower stations are among the most interesting technologies for this purpose and already exist with high capacities. This does not hold true for every individual country, however. The currently installed capacity in Germany is only 1.4 GW with a storage volume of 0.3 TWh, which in itself cannot provide any major contribution to long term regulation. The combination of such facilities, however, would play a significant role in a highly interconnected European electricity network. The Scandinavian NORDEL power system currently has an installed capacity of about 46 GW and a storage volume of approx. 120 TWh (s. also [Nor 97a] and [Nor 97b]). In the UCTE grid, to which Germany likewise belongs, the corresponding values are 49 GW and 57 TWh [UCTE 98] [UCTE 00]. The total storage capacity of the NORDEL and UCTE grid systems is thus equivalent to more than a month of average consumption in the EU and Norway combined. Dedicating these plants to the prevention of power shortages from other production would alter their routine operation, but could enable a very efficient system to be realized. It would probably also be worthwhile to increase the installed generating capacities of the storage hydropower plants, thereby increasing the ratio of rated generation capacity to storage volume to permit the compensation of additional fluctuating generation from other renewable sources. Only if the momentary output of resource-constrained power stations exceeds demand, and storage capacities are likewise filled also for all pumped storage facilities, will a portion of the potential renewable electricity generation go unused.

The better the renewable energy generation corresponds with the temporal electricity demand, the smaller the power requirements and the necessary storage capacities of the storage power plants engaged for backup purposes (s. [CDHK 99]). Generation variations may be smoothed by increasing the geographic distribution of the plants delivering fluctuating electricity ([CE 01]). In general, the expanse of the area required for smoothing increases with the length of time required to compensate for changes in production level. Seasonal variations require bridging distances of several thousand kilometers. The temporal smoothing effect differs according to the type of renewable energy and the technology employed as well as a more or less appropriate combination of the various production sites.