4. Conclusion

Energy storage using hydraulic pumping and turbining is set to continue its international expansion, in line with the continued development of solar and wind power. In fact, it represents the least expensive of all electricity-generating energy storage solutions, and is highly energy-efficient. To provide grids with the flexibility needed by power systems, energy storage competes with gas-burning, CO ₂ -emitting peak generation resources. Continued development of energy storage requires economic valuation of the many services rendered to power systems:

• shift from off-peak to peak hours and complement intermittent energies, which are the primary motivations for developing storage ;

• frequency and voltage control ;

• availability of...