One of the ways to capture energy from the ocean is through temperature. Ocean thermal energy conversion (OTEC) is a renewable energy technology that uses the ocean’s temperature variations to create electricity. For those of us who have been in ocean waters, the temperature difference between the sun-warmed surface and a few meters below the surface is noticeable. Temperature differences increase with depth. OTEC is particularly viable for tropical regions where there is a 20 degrees Celsius difference or more between surface and deepwater temperatures.
An OTEC facility has three main phases. First, warm water is introduced into a closed loop system containing a low boiling point carrier liquid such as ammonia. The warm water vaporizes the ammonia, which then passes through an electricity-generating turbine. The vapor’s pressure is then dropped by a condenser connected to the inflow of cold seawater. The now liquid ammonia begins the energy cycle again by being reintroduced to warm water.
The upfront costs of an OTEC facility are substantial, especially compared to long-term maintenance costs of the facility. Cost effective strategies factor location and materials. Ideal sites involve deep ocean waters with nearby shorelines. The piping system to bring cold water up is often one of the most expensive aspects of the facility, but evolution of cheaper, lighter weight and more durable materials will bring these costs down. Additionally, implementers are trying to increase efficiency by using waste heat from industrial processes to increase ocean water temperature differences.
The U.S. government has varied in its funding of OTEC technologies. In the 1970s, funding was provided for research and development but this funding has decreased and today, there is no official subsidy program to finance start up costs. Without the government subsidies that other renewable energy technologies experience, it is difficult for OTEC facilities to gain traction as viable, widely implemented energy sources. In spite of the history, stakeholders are optimistic that rising energy costs, increased concern for global warming and political commitment for energy security will make OTEC commercialization an attractive energy option in the future.