Energy Storage Materials:

There is a lot of problem in storing electricity in large quantities. Energy Storage Materials which can be converted into electricity can be stored in a number of ways. Storage of any nature is however very costly and its economics must be worked out properly. Various options available are: pumped storage, com-pressed air, heat, hydrogen gas, secondary batteries, flywheels and superconducting coils.

As already mentioned, gas turbines are normally used for meeting peak loads but are very expensive. A significant amount of storage capable of instantaneous use would be better way of meeting such peak loads, and so far the most important way is to have a pumped storage plant as discussed earlier. Other methods are discussed below very briefly.

Secondary Batteries:

Large scale battery use is almost ruled out and they will be used for battery powered vehicles and local fluctuating energy sources such as wind mills or solar. The most widely used storage battery is the lead acid battery, invented by Plante in 1860. Sodium-sulphur battery (200 Wh/kg) and other combinations of materials are also being developed to get more output and storage per unit weight.

Fuel Cells:

A fuel cell converts chemical energy of a fuel into electricity directly, with no intermediate combustion cycle. In the fuel cell, hydrogen is supplied to the negative electrode and oxygen (or air) to the positive. Hydrogen and oxygen are combined to give water and electricity. The porous electrodes allow hydrogen ions to pass. The main reason why fuel cells are not in wide use is their cost (> $ 2000/kW). Global electricity generating capacity from full cells will grow from just 75 MW in 2001 to 15000 MW by 2010. US, Germany and Japan may take lead for this.

Hydrogen Energy Systems:

Hydrogen can be used as a medium for energy transmission and storage. Electrolysis is a well-established commercial process yielding pure hydrogen. H2 can be converted very efficiently back to electricity by means of fuel cells. Also the use of hydrogen as fuel for aircraft and automobiles could encourage its large scale production, storage and distribution.