The global total primary energy supply and demand has doubled between 1971 and 2012, mainly relying on fossil fuels. This affects the world’s environment in aspects such as climate change and other long term effects mainly caused by the increase in quantity of greenhouse gases (GHGs) emissions. Moreover, the present constant use of combustion fuels such as oil and natural gas will result in an expected depletion in 2050 onwards. Therefore, the need of renewable
energy sources has increased during the last years in order to meet the world energy demand and progressively divert fossil energy sources. One of these new renewable energy sources is the so-called ‘Blue Energy’ or ‘Salinity Gradient Power’ (SGP). In broad terms it is energy obtained by the controlled mixing of a stream of saltwater (e.g. seas) and a stream of less saline water, treated wastewater or fresh river water.
The most well-known and most investigated techniques to generate energy from SGP are Pressure Retarded Osmosis (PRO) and Reversed Electrodialysis (RED), herein respectively transport of water or ions through semi-permeable membranes takes place (for a technical summary see Appendix II).4,5 Both PRO and RED have a large potential for producing energy for the coming years and they could be used for different applications as well.
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