It is expected that fossil fuels will continue to play an important role in the medium to long term. The efficiencies of a number of regions are shown in the figure below, which highlights that the energy efficiencies are generally lower in most non-OECD countries than in OECD countries. Possible explanations for lower efficiencies include outdated generation technologies. The necessary capital for state-of-the-art technologies such as combined cycle gas turbines is not always available and the equipment requires regular maintenance in order to maintain design efficiencies. Figure 9 highlights the importance of renewable energies in the future generation mix in all regions. The upfront costs of renewable energies are usually higher compared to fossil fuel generation technologies but the operation cost is close to zero for some renewable technologies such as solar photovoltaic (PV) panels and wind turbines.