The electricity we use is generally produced through a heat engine of one type or another. The basic working principle of a heat engine revolves around extracting heat energy from any kind of fuel to carry out the operation.
Ocean Thermal Energy Conversion (OTEC) works in a similar manner in one form or another. The basic idea is that the driving force for the operation of a heat engine is not fuel. Instead, it is the heat energy present between two layers of water of the ocean. Because there exists a natural temperature gradient between ocean water layers, the operation of a fuel engine through the heat present between them is more sustainable and efficient than burning fuel.
Considering the vastness of the oceans, it is of no surprise that they would soak up a huge amount of solar energy over time. According to the National Renewable Energy Laboratory, the tropical oceans soak heat energy that is the equivalent of 250 billion barrels of fuel! Making use of even <0.005% of this energy would be enough for powering a whole country like the United States. Of course, practical barriers come in the way, and the difficulty of attaining thermal energy from the tropical oceans increases.
What is the working principle of ocean thermal energy conversion?
In the process of Ocean Thermal Energy Conversion, the warm surface water of the oceans that have a temperature of about 25°C is used to heat up a working fluid in order to vaporize it.
Typically, the fuel used in this process has a low-boiling point, one of it being ammonia. Ultimately, the vapors expand, and the turbine that has been attached to the generator starts spinning. Then, the cooler water, generally having a temperature of 5°C from the deeper ocean layers, is used to cool the vapors.
Because of the cooler water, the vapors condensed. The state of the matter changes, and we get working fluid back in liquid form. That way, it can be reused. In such a way, a continuous electricity-generating cycle can be made with the help of the thermal gradient present between the layers of the ocean.
The effectiveness of the system is directly reliant on the temperature differential present between the layers. The more the temperature difference, the more energy is produced by the generator. Hence, the OTEC technology is viable primarily in tropical areas where the year-round thermal differential between the layers is at least -20°C.
What are the types Of OTEC systems?
Generally, there are two different kinds of Ocean Thermal Energy Conversion Systems: Open Cycle OTEC and Closed Cycle OTEC.
Open Cycle OTEC
In open cycle OTEC, no additional fluid such as ammonia is used. It is the seawater itself that is used as a form of fuel. The seawater acts as an intermediate fuel. At the hot upper layers of the ocean, the water is converted into vapors by reducing its pressure. The steam produced by the hot water turns the turbine and generates electricity in coordination with the generator.
Then, the cold water piped up from the deep inner layers of the ocean is used to convert the water vapors back into liquid. In this way, the state of the matter changes and hence can be used again. One very interesting by-product of Open Cycle OTEC is salt-free water.
The water that is once passed through an Open Cycle OTEC system comes out free of salt and impurities. In this way, these systems can also act as desalination plants. The water can be cleaned of impurities to make it usable for human consumption and irrigation purposes.
Closed Cycle OTEC
As opposed to Open Cycle OTEC, Closed Cycle OTEC uses an intermediate fuel such as ammonia, propane, and other refrigerant chemicals. These substances generally have a very low boiling point. The intermediate fluid never leaves the plant, and it stays in picking up heat from the warm water, giving it to the generator, and then returning to its original form, i.e., liquid.
First, the hot surface water of the upper layer warms up the ammonia and changes it into vapors. The heated ammonia expands to the turbine and turns it, which eventually generates electricity with the help of a generator. Lastly, the cold water turns ammonia back into liquid.
Advantages of an OTEC system
An Ocean Thermal Energy Conversion system has the following benefits:
- OTEC systems generate clean, green renewable electricity.
- The energy generated through OTEC systems does not require fossil fuels to be burnt.
- When no fossil fuels are burnt, the rate of pollution done by power plants can be decreased dramatically.
- Open Cycle OTEC can also be used as water plants in tropical areas that have a shortage of clean, fresh water.
- The “waste” water produced by OTEC systems can be used for aquaculture.
- By reducing the use of fuels and oils, OTEC supports a system that is non-fuel dependent, ultimately helping us combat water pollution and pollution in general.
Ocean Thermal Energy Conversion is one of the best ways to combat pollution, generate clean electricity, and help the crippling degenerative processes taking place on Earth. With the help of OTEC systems, we will be able to form a more sustainable world that does not run-on fossil fuels and oils. Providing a cleaner environment to forthcoming generations, ocean thermal energy conversion is the future.