Among the RET, the lights have turned to wind turbines and solar PV technologies. Taking into consideration the fact that countries such as Germany and Spain enjoy a leading position in the renewable energy sector, tangible results can be withdrawn about the situation in Europe in general if those countries used as study cases. In figure 1.1 the aggregated renewable energy capacity in Germany is shown, proving that mainly the focus is on the wind technology and PV. As far as the PV installations concerned, there is a dramatic change since 2004, when the feed-in tariff policy mechanism and relevant subsidies have been in effect. Only in 2008 around 1.5 GWp were installed in Germany [5], while in September of 2010 the total number of installed capacity was 15 GWp, which is the 30% of the total RET installed and the 37.5% of the minimum load of electricity in 2009 as is seen in figure 1.1.