The world’s energy consumption has grown rapidly during the previous century and it is still growing fast. Especially the need for electricity has grown extremely rapidly. To satisfy this need, huge giga-watts thermal power plants are built in urban areas to convert world’s fossil energy resources into electricity. Simultaneously, the world community starts to realize that changes are needed for mainly two reasons:

1. World’s fossil energy resources are limited and we will approach the end of these resources sooner or later.
2. Discharge of gasses associated with the use of fossil fuel may threaten theenvironment and health of people.