Ocean energy is a form of renewable power that captures the continuous forces found within the world’s oceans. This energy is derived from the movement of water, such as tides and waves, and from the thermal properties of the seawater itself. Harnessing these natural phenomena allows for the generation of clean electricity and offers a stable alternative to traditional power sources.
The Diverse Forms of Ocean Energy
Energy can be captured from the ocean through several distinct technologies that target different marine forces. Tidal power, one of the most developed forms, captures energy from the predictable, cyclical rise and fall of sea levels caused by the gravitational pull of the moon and sun. This is achieved either through tidal barrages, which trap a large volume of water and release it through turbines, or by tidal stream generators, which are underwater turbines that capture the kinetic energy of fast-moving currents.
Wave power is another method that focuses on the kinetic energy of surface motion, where devices known as wave energy converters (WECs) absorb the movement of wind-driven waves. These converters use the wave’s motion to drive hydraulic systems or linear generators to produce electricity.
Ocean Thermal Energy Conversion (OTEC) operates on a different principle by exploiting the temperature difference between warm surface water and the much colder deep water, typically found a kilometer below the surface. This temperature gradient is used to run a heat engine, often using a working fluid like ammonia, to generate power.
Ocean current energy, distinct from tidal streams, focuses on the persistent, non-tidal flow of major ocean currents, such as the Gulf Stream. These currents are driven by factors like wind, temperature, and salinity differences, offering a reliable, continuous flow that can be captured by sub-surface turbines.
Primary Application: Integration into Electrical Grids
The main purpose of large-scale ocean energy facilities is to generate electricity for widespread distribution through established electrical grids. Unlike solar and wind power, which are intermittent, tidal energy offers a highly predictable source of power that is known years in advance. This predictability allows tidal systems to serve as a reliable source of base-load power, which is the minimum amount of electric power needed to be supplied to the electrical grid at all times.
The conversion process begins when the force of the moving water or the thermal gradient drives a turbine to spin, transforming the ocean’s kinetic or thermal energy into rotational mechanical energy. This mechanical energy then turns a generator, which produces variable alternating current (AC) electricity.
Since the speed of the water flow or the temperature difference can fluctuate, the generated AC power often needs to be conditioned before it can be transmitted. Power conditioning is accomplished using a series of power converters and inverters, which first rectify the variable AC output into direct current (DC). The electricity is then converted back into stable AC power at the correct frequency and voltage required by the onshore grid infrastructure. High-voltage subsea cables transport this conditioned electricity from the offshore plant to a substation on land, where it is stepped up for long-distance transmission. Integrating ocean energy helps coastal population centers by supplementing existing renewable portfolios, enhancing overall grid stability and resilience.
Direct and Specialized Uses
Beyond large-scale grid integration, ocean energy is also utilized in specialized, localized applications, often leveraging the technology’s byproducts.
Seawater Air Conditioning (SWAC)
Ocean Thermal Energy Conversion (OTEC) plants draw large volumes of cold, deep seawater to the surface, which is then used for various purposes after power generation. This cold water is instrumental in Seawater Air Conditioning (SWAC) systems, where it is circulated to cool buildings directly, significantly reducing energy consumption compared to conventional air conditioning.
Desalination
The OTEC process can also be paired with desalination to produce fresh, potable water. Open-cycle OTEC systems flash-evaporate warm surface water to drive a turbine, and the resulting steam is condensed by the cold deep water, yielding desalinated water as a clean byproduct. Alternatively, wave and tidal energy can be used to directly power reverse osmosis desalination units by using the ocean’s mechanical force to pressurize the seawater, bypassing the need for an electrical conversion step.
Off-Grid Power and Aquaculture
These specialized uses are particularly beneficial for remote island nations and coastal communities where energy and fresh water resources are scarce or expensive. Small-scale ocean energy systems can provide power to off-grid applications such as deep-sea monitoring equipment, navigational buoys, and remote scientific stations. The cold, nutrient-rich deep seawater brought up by OTEC is also used to support cold-water aquaculture, creating a multi-use facility that generates power, water, and food.