Introduction:
Providing safe, environmentally friendly, and reliable energy supplies is essential for having a sustainable and high quality life, but they are subjected to social, political, environmental and economical challenges. It is generally agreed that no single energy source will dominatethe energy market and hence energy-mix model is the way to go, depending on the availability of usable resources in each region/country or the options of importing these resources. The future energy network would include a combination of different technologies (Whitesides & Crabtree, 2007). To generate sufficient energy or power for surging energy demand, not only the technologies but also their potential social, political, environmental and economical impacts must be taken into account carefully. Improving energy efficiency and increasing the contribution of carbon-free fuels in energy supply will be effective in developing an efficient and a more sustainable future. To achieve this objective, fundamental understanding on different aspects of these technologies should not be neglected (Gao et al., 2013), (Whitesides & Crabtree, 2007), (Zhang et al., 2013), (Tozzini & Pellegrini, 2013)
Renewable energy resources are playing and will play a vital role in meeting current and future energy needs. They are also a key component in the sustainable development. The origin of renewable energies is associated with the energy from the sun. They are more environmentally friendly compared to the conven- tional fossil energy sources and will not be depleted within the foreseeable future. Above all, they make the decentralization of electricity networks a possibility. Therefore, they improve the flexibility of the energy system and provide economical advantages for off-the-grid applications due to the nature of distributed generation. However, existing issues including high cost, intermittency of energy supply, grid connection and storage challenges
(Aghaei & Alizadeh, 2013), (Devabhaktuni et al., 2013), (Gahleitner, 2013), (Jebaselvi & Paramasivam, 2013), (Tan et al., 2013) should be addressed before the penetration of renewable energy in the energy market would be significant. Small output renewable energy sources could easily be balanced within the energy network, but the large incrementing percentage of global renewable power highlights a substantial need for energy storage. The prediction of market penetration of renewable energy resources is controversial as different organizations might predict the growth according to their interests. For instance, an oil company would downplay the growth; a renewable energy instrumentation company would project the biggest renewable energy penetration, while a conservative organization would predict some moderate penetration. Fig. 1 presents the range of projections made by the three groups representing three different types of companies mentioned.