Energy storage: the weak point of the energy sector

T toring surplus energy for later needs is now a necessity.

Storage makes it possible to defer energy consumption relative to its production, so that supply need not respond instantaneously to demand.

Electricity or heat energy can be stored. There are many storage technologies; some of which will be described in this article, but for them to be economically viable they must be reliable, safe, and flexible, etc. Most of these multiple constraints have been partly met, but constant improvement is still needed. Despite a wealth of technologies, storage remains a weak point in the energy sector. A breakthrough in this area would completely transform the energy landscape and have profound geopolitical consequences.

Electricity storage allows power production to be smoothed: the surplus of off-peak periods is stored for use when demand is high. In this way, electricity can be stored when its price is low and sold when its price is high. In intermittent electricity generation, such as from wind turbines or photovoltaic solar panels, production is often out of phase with demand. Storage is then indispensable so that other, high-pollution energy sources are not needed to take up slack.

Even outside windless or sunless periods, wide fluctuations occur in wind-powered or solar electricity production. Storage enables us to smooth these fluctuations. The widespread development of these intermittent renewable energy sources will thus require extensive deployment of storage capabilities.

Mobile devices (smartphones, portable computers, audio and video players, etc.) are omnipresent in modern society. Hybrid, plug-in hybrid and electric vehicles are rapidly developing. The weak point of these vehicles and of mobile devices is most often their energy supply. Rechargeable batteries are at present the only practical way to power them until fuel cells have been developed, which will take time. But even with these, the problem of fuel storage will arise.

Thermal energy (heat or cold), which is the lowest grade energy, also holds an important place in modern society. Heat or cold are fairly easy to store for short times (e.g. cumulus or ice), but less so for long periods, such as from one season to the next.

This article is an introduction to the field of energy storage. Several aspects of this field are presented. Interested readers can find further information in the reference articles cited. The storage field is slowly but continuously evolving. The data given here are to be taken as indicative as they can differ to some extent from one industrial plant to another, and among laboratory...