Abstract
The oceans and seas, covering more than two-thirds of the Earth, represent an enormous energy resource containing vastly more energy than the human race could possibly use. In four days they absorb an amount of thermal and kinetic energy that is equivalent to all the world's known oil reserves. The energy is partly stored as kinetic energy from the motion of waves and currents and partly as thermal energy from the Sun. As the ultimate source of energy is the Sun, marine energy is renewable, providing relatively clean energy when compared to conventional sources such as coal, oil, and natural gas. The main marine energy resources can be summarised, in order of maturity and use, as follows: tidal energy, wave energy, tidal/marine currents, ocean thermal energy conversion (OTEC), salinity gradient/osmotic energy, and marine biomass fuels. Ocean and sea energy is one of the most promising new renewable energy sources and is deserving of further investment. Furthermore, the know-how is now available to combine existing technologies to utilize marine energy for power generation. The paper will present the worldwide potential of marine energy, technologies for its exploitation, as well as examples of existing devices and plants. Special attention in the paper will be devoted to the potential assessment of the marine energy of the Adriatic Sea in the Republic of Croatia, as well as the possibilities of its exploitation.