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With considering the increasing of global temperature, and also the concern of global climate change, many policy makers worldwide have been accepted the importance of reducing greenhouse gas emissions, in particular from the power industries so the importance of the renewable energy is obvious. Wave energy is one of the renewable energy sources. And has the potential to play a valuable part in a sustainable energy future. Wave energy is also one of the predictable energy sources that depending on oscillating the surface of water. The wave energy system for generation electricity in the last few years has been growing rapidly. There are several methods that have been proposed to classify wave energy converters with considering working principle, location and size such as the oscillating water column (OWC), oscillating body systems, overtopping converters and etc. In almost every system, optimal wave energy absorption includes some kind of resonance, which implies that the geometry and size of the structure are linked to wavelength. The resonance allows to relatively small device to producing large power. This paper discusses about the various technology of wave energy converters.

Increasing the greenhouse gases concentration, climate change and the global concerns about the fossil fuels pollutants lead scientists and researcher toward the energy production by the renewable energy sources. Replaced the energy generation sources from the fossil fuels to the renewable energy sources is one of the important project that scientists and researchers has been worked and the good potentials of this sources of energy make them to most studies and researchers from this important. Salinity gradient energy or blue energy is an of the high potential energy sources that placed in renewable energy's list. The salinity gradient energy can be one of the important sources of the renewable energy to electricity generation for global electrical demand in future. When saline and fresh water mixes the Gibbs free energy is released. This energy could be used for generation of electrical power by some methods. There are two promising techniques for the generation energy from salinity gradient including RED and PRO methods. According the estimates of power available in the world salinity gradients energy are estimated between 1.4 and 2.6 TW, this amount of power generation in comparison to other marine renewable energy sources is a good potential. This paper is over review for salinity gradient energy, RED and PRO methods.