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Energy Storage


Storing electricity or heat is a strategic issue to respond to daily fluctuations and peak demands. Intermittent energies (solar, wind) being subject to great fluctuations, the storage of electricity makes it possible to smooth the variations of production and to reduce the use of fossil fuel plants. Portable electronic devices, plug-in or electric hybrid vehicles require high-performance rechargeable batteries. The storage of thermal energy is a major problem in terms of energy supply. Heat can be stored in the short term (for example, an electric water heater), but is more difficult in the long term (seasonal storage).

 ABSTRACT

Energy storage: the weak point of the energy sector

The storage of electricity or heat is a strategic issue. Storing large quantities of electricity during off-peak hours helps to absorb daily fluctuations and peak demands. Solar energy and wind energy are available intermittently, and are subject to wide fluctuations. Electricity storage smooths out these variations in output and reduces the use of fossil fuel plants. Portable devices for communication and entertainment, and plug-in hybrid and electric vehicles require high-performance rechargeable batteries. Storing thermal energy (in the form of heat or cold) is a major issue in energy supply considerations. Heat can be stored in the short term (e.g. an electric water heater) but is more difficult in the long term (inter-seasonal storage).

INTRODUCTION

Storing energy when you have too much to use when you need it is a necessity. Storage makes it possible to defer a use of energy in relation to its production, thus avoiding at every moment the demand and supply being equal. We can store electricity or heat. There are many storage technologies and we will describe some of them in this article, but for them to be applicable they must be economically viable. They must be reliable, safe, flexible, and so on. This is a lot of constraints that are, for the most part, partially resolved and require constant improvements. Although there is a proliferation of technologies, storage remains the weak point of the energy sector. A break in this area would completely change the energy landscape and have profound geopolitical consequences.

The storage of electricity helps to smooth the production of electricity: the excess of off-peak hours is stored for use during peak hours. This makes it possible to store electricity when it is not expensive to sell it when it is expensive. For intermittent energies, such as wind or solar photovoltaic whose production is often not in line with demand, storage is essential or it is necessary to use complementary sources of energy polluting to produce electricity when they do not generate it. In addition to the fact that some periods are without wind or without sun, there are significant fluctuations in production when there is sun or wind. Storage helps to smooth these fluctuations. A wide development of intermittent renewable energies (solar and wind) will therefore require in the future a major deployment of storage facilities.

Mobile devices (smartphones, laptops, audio or video players, etc.) have invaded modern society. Hybrid, plug-in hybrid and electric vehicles are in full development. The weak point of these vehicles and nomadic devices is most of the time their power supply. Rechargeable batteries are for the moment the only practical way to power them while waiting, more or less quickly, the development of fuel cells. But even with this hypothesis, there will be the problem of fuel storage.

Thermal energy (heat or cold), which represents the most degraded form of energy, also occupies an important place in modern society. The heat or the cold can be quite easily stored in the short term (example: cumulus or ice) but more difficult in the long term (inter-seasonal storage).

This article is an introduction to the field of storage of which it presents some aspects. It may be supplemented by reference articles if the reader wishes to have more details on a particular topic. The storage domain is evolving slowly but continuously. The data quoted here should be taken as indicative since they may differ more or less from one industrial implementation to another as well as on laboratory prototypes which are constantly improved.

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