What
is OTEC?
Other than electricity generation, what else can an OTEC
plant be used for?
What region is an OTEC plant most suitable to?
What are the advantages of OTEC?
What are the disadvantages of OTEC?
The main objective of ocean thermal energy or Ocean Thermal Energy Conversion (OTEC) is to turn the solar energy trapped by the ocean into useable energy. This kind of energy is found in tropical oceans where the water temperature differs from surface to deeper into the sea. On the ocean surface it can be at least 20 C hotter or cooler than the temperature at a deeper sea level. So far, this concept of producing energy is still experimental, although it is at least a century old; created by the French engineer Jacques D'Arsonval in 1881. Three approaches, open cycle OTEC, closed cycle OTEC and hybrid cycle OTEC have been created in the past fifty years. Currently, the Natural Energy Laboratory of Hawaii hosts the world's only operating experimental OTEC plant.1
| Closed Cycle OTEC: | Closed Cycle OTEC employs a low-boiling-point liquid like propane or ammonia as an intermediate fluid. The OTEC plant first pumps in the warm sea water and boils the intermediate fluid. Then, the intermediate fluid vapor pushes the turbine to generate electricity. Finally, the vapor is cooled down by cold sea water. The first closed cycle OTEC was built by French Ministry of Colonies and the Centre National de la Recherche Scientifique in 1942.2 Unfortunately, the operation of that project didn't last long because the cost of OTEC was much higher than that of the conventional sources of energy available at that time. |
| Open Cycle OTEC: | Open cycle OTEC is very similar to the closed cycle one. The only difference is that an open cycle OTEC does not use intermediate fluid: the sea water is the fluid that pushes the turbine. The warm sea water on the ocean surface is turned into low-pressure vapor under a partly vacuumed environment.3 This low-pressure vapor can then push the turbine. Later, the vapor will be cooled down and turned into desalinated water by the colder water deeper into the ocean. |
| Hybrid Cycle OTEC: | Hybrid Cycle OTEC is a theoretical method of maximizing the use of ocean thermal energy. There are two concepts. The first one is to use a closed cycle OTEC to generate electricity to create the necessary low-pressure environment for the open cycle OTEC. The second concept is to integrate two open cycle OTEC (one is used to create the vacuumed environment) so that there will be twice the amount of the original desalinated water. 4 |
Other than electricity generation, what else can an OTEC plant be used for?
Other than generating electricity, open cycle and hybrid cycle OTEC plants can also produce desalinated water, which can be used for irrigation and human consumption. A closed cycle OTEC plant can also act as a chemical treatment plant. An OTEC plant can also be used to pump up the deep sea water. The cold water can then be used for air conditioning and refrigeration if it is brought back to shore. In addition, while the sea water surrounding the plant is being moderated, the enclosing area can be used for aquaculture and mariculture.5
What region is an OTEC plant most suitable to?
OTEC plants are most suitable for islands around the tropical region of the east Pacific Ocean. This is because OTEC plants can provide both energy and pure water at the same time with a relatively low cost. It is also because the ocean in that region has greater temperature differences, which is about 24 oC.6
What are the advantages of OTEC?
The variety of products and services are the major advantage of OTEC plants. Ocean thermal is also relatively clean and will not produce more pollutants that contribute to global warming.
What are the disadvantages of OTEC?
Despite the advantages of temperature moderation, the OTEC plants can alter and maybe damage the surrounding ecosystem. Also, pollution can be caused by closed cycle OTEC if intermediate chemicals leak into the ocean.
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