Osmotic energy, also known as osmotic power or salinity gradient power, is a form of renewable energy that harnesses the energy available from the difference in salt concentration between seawater and freshwater. When freshwater moves from a solution of lower concentration to a solution of higher concentration across a semi-permeable membrane, it creates a pressure known as osmotic pressure, which can be converted into energy. The key element of this technology is a semi-permeable, double-sided membrane that lets water through but captures mineral salts. The diluted, brackish water from the membrane module is split into two flows: freshwater and brackish water. The freshwater is then used to generate electricity by driving a turbine.

Osmotic energy is a rapidly growing renewable energy source that is reliable and produces no pollutants. The first prototype osmotic power plant was opened in Norway in 2009, and the full-scale plant was intended to be ready by 2015. Osmotic power is thought to have a global potential of up to 1700 TeraWatt hours.