How will the role of pumped storage evolve?

Pumped storage will become increasingly important in the context of energy transition, even if it is not cost-effective today. Increasingly, these facilities will be required to store excess electricity from intermittent renewables (solar, wind).

Demand for electricity is not constant. It varies constantly: typically 45% between day and night, 20% between weekdays and weekend, and 30% between summer and winter. Some power plants, especially nuclear power plants, must, for technical and economic reasons, operate continuously to keep their output as constant as possible on a seasonal basis. Similarly, run-of-river hydroelectric plants (without storage lakes) have only a small capacity to modulate their output. They produce continuously, mainly in the summer, when demand is lowest.

This makes it difficult for the power generation system in its current configuration to keep up with changes in demand. The result is over-production of electricity during periods of low consumption. For decades, Switzerland has been using its pumped storage facilities to store excess electricity (mainly at night) and then return it to the grid the next day when demand is high, with a profit margin in the process [→ Q66].

In the context of the energy transition, irregular renewable energy sources (solar, wind) will develop strongly. Consequently, pumped storage plants are expected to continue to grow in importance.

As wind and solar energy are so-called intermittent energy sources, the variation of their production according to weather conditions can only be predicted a few hours or days in advance. Since production must always be equal to consumption [→ Q72], surplus electricity must be disposed of by storing it in another form for future use. Thanks to our alpine dams, we have an attractive storage capacity for surplus solar and wind power generation. These storage capacities are naturally of interest to western European countries, especially for surplus solar power from the south and wind power from the north. For this reason, Switzerland is currently increasing its pumped storage potential and plans to upgrade some of its dams [→ Q76].

In Switzerland, there is nothing anecdotal about pumped storage; for every 100 litres of water entering the storage lakes of our dams (rainwater or snowmelt water), 12 litres are pumped from the plain. On a Swiss and even more on a European scale, the demand for pumped storage could increase significantly in scenarios that foresee a strong increase in the flow of electricity from renewable sources. Several major pumped storage facilities are currently under construction or in the planning stage, the largest of which are the Linth-Limmern facility in Glarus and the Nant-de-Drance facility in Valais (commissioning planned for 2021).

Paradoxically, the deployment of new, heavily subsidised renewable energies (solar and wind power), which creates the need for additional storage capacity, is contributing to endangering the economic viability of pumped-storage facilities. Without a massive increase in electricity prices, particularly through a rise in the price of CO₂, these facilities are likely to be unprofitable [→ Q70].