Seas and oceans are used as a source of fossil fuels, oil and gas, but the exploitation of their potential as a renewable energy sources (RES) is still in the development phase. According to estimates by the European Commission, only 0.1 % of the energy that could be obtained from the ocean is five times greater than the total energy needs worldwide. However, the main reasons of low marine energy exploitation are expensive power technology and large infrastructure limitations.
Oceans cover more than 70% of the Earth’s surface and thus represent a very interesting source of energy that could provide more energy to households and industrial plants in the future. Today, there are an insufficient number of power plants that use the energy of the ocean, and these plants are generally.
In the coastal areas, there are three basic ways of marine energy (ocean energy) exploitation:
- The use of wave energy – mechanical energy of the sea wave movement
- Use of tidal energy, also called tidal power
- Energy production from temperature differences of ocean water – known as “Ocean thermal energy conversion”
Wave energy is a form of kinetic energy that occurs during movement of ocean waves caused by blowing winds. This type of marine energy can be used to initiate turbines in areas where winds are strong enough to produce a constant movement of the sea waves.
Wave energy is “captured” directly underneath the surface waves, because this energy rapidly decreases with the depth of the ocean. At a depth of 20 m it is only 20 % of energy just below the surface, and at a depth of 50 m only about 2 %. The most common way of using wave energy is: wave rises into the chamber; rising water forces displace air from the chamber; mobile air then drives a turbine and turbine drives a generator.
The main problem of wave energy is the fact that this marine energy source cannot be used uniformly in all parts of the world. Many studies have been dedicated to solving this problem.
Tidal energy (tidal power)
Tidal power occurs due to the gravitational forces of the moon and sun on the water in the oceans. For utilization, it is necessary to select a suitable place on the coast, where there is a large tidal range. The simplest way of using marine energy is achieved by creating a storage pool (reservoir) and installation of turbines that operate in one direction only.
During high tide the water enters the storage reservoir until it reaches the maximum level. With the advent of low tide, the water is drained from the pool through the turbines. In this way, the potential energy of water accumulated in the pool transforms into mechanical energy and then into electricity.
Ocean thermal energy conversion (OTEC)
This is a method of electricity production based on the temperature difference between deep and shallow water (the water is colder at greater depths of the ocean). The minimum temperature difference should be 38°F.
There are three basic types of ocean thermal energy conversion:
- Closed-Cycle systems
- Open-Cycle systems
- Hybrid energy systems
OTEC systems require expensive, big pipes of large diameter. The pipes must be set on a great sea depth (at least one kilometer) that could bring colder water from the depths. OTEC power plants require a very large initial investment and plenty of space to build. All this makes it difficult for the exploitation of marine energy. Recommended reading: Learn About Marine Energy.