This is partly explained by the availability of renewable energy sources which is high for instance in Nordic countries, benefiting from large hydroelectric capacities. In Germany, wind and biomass account for two thirds of the RES electricity production, while hydropower and solar remain limited (20% and 7%). Uncertainty regarding environmental policies hampered the development of RES in other OECD countries (OECD, 2011a). Some studies also show that feed-in tariffs were more efficient than other policies in increasing RES penetration.