The growth of renewable energies, the development of new uses for energy such as electrical mobility and self-consumption, provision for isolated locations, and so on — a number of factors explain the bullish growth across the storage sector. In fact, energy storage is of particular interest for smoothing demand fluctuations and addressing the peaks in consumption generally seen towards 7.30pm and which, so far, are covered by falling back on fossil-fuelled power stations or even by importing electricity.
Today no less than eight technologies are recognised as offering storage for electrical energy, heat, or cold, and research continues to uncover new options. These technologies divide into two main groups: stationary storage, permitting “usage to be displaced temporally without being displaced spatially” (Ademe) so enabling balance to be achieved between production and consumption, and attached or portable storage dedicated to mobile applications (primarily batteries). However, batteries are also employed for stationary applications, particularly for self-consumption, micro-grids or working alongside intelligent networks.
Electricity storage solutions
In order to be stored, electricity must be transformed. In the case of pumped hydroelectric storage (PHS) facilities, this takes the form of potential energy storage in a mass of water (i.e. two water reservoirs at different heights). As of today, pumped storage represents over 90% of energy storage capacity in the EU. In the case of CAES (Compressed air energy storage), this — as the name suggests — is storage using compressed air, most commonly held in underground caverns: such thermodynamic storage offers both high capacity and extended duration. These two systems (PHS and CAES) generate electricity via a turbine.
A technology that has long been familiar, the flywheel storage system allows kinetic energy to be created (via a rotating mass, frequently cylindrical in form) which is subsequently recovered via an alternator in the same way as a dynamo. This mobilisable solution enables ad-hoc adjustments to be made, and recent innovations offer very high recovery (up to 97% from the Levisys solutions, for example).
Then battery storage uses electro-chemical reactions through the circulation of electrons between two electrodes. The materials used may be varied (lead, lithium-ion, sodium-sulphur, nickel-cadmium etc.) While some are working with 4th generation Li-ion batteries, others are developing lithium-free solutions (see box).
Heat storage solutions
Less often highlighted, but just as crucial on the path to decarbonisation, heat storage technologies are also diverse. Thermal energy may be stored in the form of latent heat (using ice or phase-change materials), as sensible heat (using hot water or molten salt) or in chemical form (via reversible chemical reactions or hydrogen production). Another solution, electromagnetic storage (SMES – Superconducting magnetic energy storage), is based on the creation of an electric field in a spool and allows rapid recovery of the energy produced.
Advances in research
Current research activity aims at several objectives: offering materials at lower cost, reducing the quantities of materials or chemical substances used, identifying the best-performing chemical pairings for batteries, reducing losses and so raising outputs, planning installation and maintenance costs etc. Thus, for example, IFPEN is working to improve the output from CAES up to 70%. Other work is aimed at developing new CAES solutions or optimising thermal storage in aquifers.
Towards a European storage strategy
Beyond the media buzz unleashed in 2017 by the announcement of the European Battery Alliance, aimed at increasing battery production within the EU, the European Parliament has set its sights on a genuine dedicated European strategy. At least, this is what was called for in a Resolution on 10 July 2020 because, as recently as 2018, less than 3% of global Li-ion battery production was located within the EU, cf 85% in the Asia-Pacific region. More widely, the Commission estimates that the EU needs to be in a position to store six times more energy than today if it is to attain its objective of greenhouse gas emission neutrality by 2050.
Ultimately, whether it be chemical, electrochemical, mechanical or thermal, energy storage solutions offer a great variety of applications that reach far beyond merely the storage of solar or wind energy. Following a 30% decline in 2019 cf 2018 (with 2.9 GW added), the global development of large-scale storage capacities appears to be on the rise once more: a recent study by the specialist consultancy Clean Horizon reported in GreenUnivers shows 8.6 GW of projects have already been announced as at the beginning of May (excluding PHS) – that’s equivalent to the total for the whole of 2019. This bodes well for a promising 2021. Among the more dynamic developers, France’s Neoen ranks in 3rd place, behind America’s NextEra and Solar Philippines (see box).