Ocean current energy is a form of renewable energy harnessed from the continuous, predictable flow of ocean currents. These currents, driven by wind, tides, and differences in water density, offer a steady and reliable source of energy. Devices known as marine current turbines or underwater turbines are used to capture this energy. These turbines operate similarly to wind turbines but are placed underwater, where they are driven by the moving water. Ocean current energy is particularly advantageous due to its high predictability and consistency, providing a reliable source of power. It can be used for electricity generation and integrated with other renewable energy sources to enhance energy security and reduce reliance on fossil fuels. 

Ocean Salinity Gradient Energy harnesses the energy released from the difference in salt concentration between seawater and freshwater, employing methods like pressure retarded osmosis (PRO) and reverse electrodialysis (RED). PRO utilizes a semi-permeable membrane to induce osmotic pressure, driving a turbine for electricity generation, while RED uses ion exchange membranes to create an electric potential from ionic differences. This renewable energy source is particularly advantageous due to its sustainability, low environmental impact, and potential integration with desalination processes, though it faces challenges such as high initial costs and technological complexities, limiting widespread adoption.