The human population increase along with the raise of living standards is about to cause doubling of the global primary energy consumption in less than 50 years [1]. Such continuous increase of energy demand will soon become unsustainable when considering that most of the currently exploited energy comes from fossil fuels whose resources are, obviously, limited. Moreover, burning of fossil fuels by the humankind in the past 250 years released such a quantity of carbon (in the form of CO2—an important greenhouse gas) that it took our planet about 250 million of years to sequester [2]. An increasing awareness comes up on the energy demand issue and new pressing challenges arise to provide people with enough energy within a sustainable development scenario.