Green electricity is the cleanest, most beneficial forms of renewable energy. For example, municipal solid waste or large scale hydro-power are indeed renewable but still have major polluting capacity. These are the energy sources considered to provide green electricity. Currently, the usable energy is basically harvested from the fossil energy sources, including coal, oil, and gas, which are believed to harm the environment due to the emitted GHGs. The awareness to the climate change and limited reserve of fossil energy sources has led to a strong motivation to develop a new energy system which can facilitate three important pillars: security, clean environment, and economic opportunity. This future energy system is strongly expected to be able to blend both fossil and renewable energy sources, while minimize its environmental impacts. To realize it, the primary energy sources are converted to the efficient secondary energy sources, including electricity and hydrogen. These two kinds of secondary energy source are considered very promising in the future, following a high demand in many sectors. In transportation sector, both electricity and hydrogen are believed to become the future fuels as the deployment of electric and fuel cell vehicles is increasing rapidly.
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