The world’s Hexanoylcarnitine map has changed dramatically during the last 40 years (Fig. 1), not only in the increase in the demand for all of the energy sources but also in the contributions of each source at a global level. Thus, at a European level, oil has changed from being the main energy source to sharing the first position with natural gas and coal . The situation in the European area is equivalent to the situation in the whole world. Currently, the EU is undergoing some challenges, including an economic crisis and the growing atmospheric concentration of CO2, in addition to a specific and very preoccupying concern: the insecurity in the energy supply due to a great dependence on outside energy sources . To be able to face this situation, it is necessary to establish some decision criteria that can improve the energy efficiency of all of the processes and activities in fostering the use of renewable energies ,  and .
Fig. 1. Impact of the economic crisis on energy consumption (Mtoe) and CO2 emissions (million tonnes carbon dioxide) in EU. Own preparation based on: BP Statistical Review of World Energy .Figure optionsDownload full-size imageDownload as PowerPoint slide