ABSTRACT
Accelerated development of humanity has the effect of increasing energy demand worldwide. The annual reports of International Energy Agency (IEA) show that the total energy consumption increased from 196 EJ in 1973 to more than 350 EJ in 2009 (1 EJ = 1018 J) (Schlagermann et al. 2012), and the tendency is upward. More important is that about 80% of energy demand is obtained from oil and other fossil fuels, whose use has two serious consequences:
1. The fossil fuel supplies are constantly diminishing-It is estimated that in Europe, oil resources will be exhausted in 40 years, natural gas in 60 years, and coal in 200 years, and this means that in about 20 years, Europe will have to import 70% of energy needs (Balat 2010).
