Overview

Energy-storage technologies can provide a vital link between the primary source of energy and its actual use. In particular, the inclusion of an energy-storage system allows flexibility in matching the availability of an energy source to the demand profile in terms of where and when power is required and at what level.

This chapter discusses the need for energy storage on the medium to very-large scale (kWh GWh) in centralized electricity supply networks and also, at a more local level, for uninterruptible power supplies and for use in conjunction with renewable energy sources. The storage of electricity for portable devices is discussed in Chapter 9, and for electric propulsion in Chapter 10.

6.1 Candidate Energy-storage Systems

As noted in Chapter 3 (Figure 3.14), several types of energy-storage system are under investigation. These may be classified according to the form in which the energy is stored, namely:

• thermal energy: storage heaters, molten salts

• potential energy: pumped hydroelectric, compressed air

• kinetic energy: flywheels

• electromagnetic energy: superconducting coils

• electrostatic energy: capacitors, supercapacitors

• chemical energy: batteries, methanol, hydrogen.

The scale of these systems ranges from miniscule elements on integrated circuits ( e.g. batteries, supercapacitors) to pumped hydroelectric reservoirs that store the equivalent of GWh of electrical energy.

The characteristics of those systems that are suitable for the medium-to-large-scale storage of electricity are summarized in Table 6.1. (Note, supercapacitors are an option only for power-quality applications in which the energy requirement is not large; further details of these devices are given in Section 7.5,...