Large-scale energy storage on the grid

A SWOT analysis by the KULeuven (Belgium) On the grid, an instantaneous balance between electricity production and highly variable demand needs to be maintained. In the past, it was not economically feasible to make widespread use of storage systems to relieve this stringent requirement, but times have changed. Since the liberalisation of the energy market and the increasing use of (variable) renewable energy sources, the role of the grid and its power quality has gained importance, creating new market opportunities for storage systems. This has in its turn  stimulated their further technical development.

A range of applications Large-scale storage systems can facilitate the integration of variable renewable energy generation. Off-peak, energy can be stored, which can be injected into the grid at peak demand. Storage systems can also flatten the load curve, requiring less peak production capacity. Once energy storage is available, it can also react to stochastic changes in demand, reducing the need for, and the use of, quickly startable reserve capacities, which have in general poor efficiency and environmental performance. Grid operators can use storage systems to improve power quality (voltage sags, flicker, surges), to provide line stability, and for Power Oscillating Damping. Energy storage can also be used for restoring power after a black out, or as a long term energy reserve.

Existing and emerging technologies The choice of the storage system depends heavily on the  application:

• For bulk storage by generation companies, pumped hydro and compressed air energy storage in underground caverns are the most suitable. Both are mature technologies with good cost-efficiency, but the development of new projects is limited by geological constraints.
• Battery energy storage systems have good technical characteristics (fast response, high energy density) but are less economic for bulk storage. They become cost-efficient if combined with other application domains.
• A relatively new technology is Superconducting Magnetic Energy Storage. Today, its use is limited to situations requiring very fast response, for example where the shortest voltage dip can be very costly. New technology breakthroughs could make it play a role in other applications domains.
• Super-capacitors have become an option for the future since new materials enhanced their performance. Further technical development could make them useful buffer devices for protecting the grid.
• Hydrogen is a much talked about emerging energy carrier. Further development of the production, storage, and conversion systems is required to make it a competitive technology. Being clean and flexible, it could play an important role in the energy supply system of the future.