The ocean is considered to be one of the most abundant places on earth because of the underwater life it has. Not only does it house a wide variety of fish but it is also a source of energy, how so? Water naturally takes time to warm up as well as cool down. With such characteristic, man has come up with the ocean thermal energy conversion as a source of a renewable green energy. Many experts believe that when this is perfected, it is an equally competitive source of a great amount of electrical power. In relation to this, it is wise to look closer into what are the things that are involved in ocean thermal energy conversion along with the other facts connected to it.
The ocean thermal energy conversion, also known as OTEC was founded on the principle of heat stored in ocean waters. Since the earth’s oceans vary in depth, the temperature of the water also differs. The top layer of the ocean is normally warmer than that of the water found in the middle and near the bottom. OTEC works best when there is at least 20 degrees Celsius or 36 degrees Fahrenheit difference in the warm top layer and cold deep ocean water. This temperature difference is often found in tropical areas. It is said that these requirements are met by the areas in between the tropics of Capricorn and Cancer.
It was Jacques Arsene d’Arsonval, a French physicist suggested that the thermal energy of the ocean can be tapped. However, in the year 1930, it is his student Georges Claude who actually built an OTEC plant in Cuba. The plant produced 22 kilowatts of electricity through the use of a low-pressure turbine. In the year 1935, George Claude again made a plant on board a 10,000-ton cargo vessel anchored to the coast of Brazil. However, this attempt was unsuccessful for the plant was destroyed by the waves and weather before it could even function. 21 years after, French physicists designed 3 Megawatt plant for use in the Abidjan, Ivory Coast in West Africa. This endeavour, too, was unsuccessful because of economic reasons and expensive costs.
The United States became involved in 1974 through the Natural Energy Laboratory of Hawaii Authority at Keahole Point on the Kona coast of Hawaii. It was said that Hawaii is the perfect place to build an OTEC plant for it has warm surface and cold deep waters. As a result, it became the OTEC leading test facility.
The first attempts to build a bigger OTEC facility were unsuccessful and there were additional studies that were made. In the year 1970, Japan was able to build a 100kW closed-cycle OTEC plant on Nauru Island. This was brought about by the Tokyo Electric Power Company and was fully operational by the year 1981. It was producing about 120 kW of electricity. 90 kW was used to sustain the OTEC plant and the electricity left was used by other places like schools. This breakthrough did set the standards and a world record which was sent to a real power grid.
Ocean thermal energy conversion involves three kinds of cycles that encompass the use of warm and cold water. The first type of cycle is the closed kind. This cycle uses low-boiling point fluids like ammonia, this then turns the turbines and in order to generate electricity. In this cycle, the warm ocean water is pumped through a heat exchanger to vaporize the fluid. The cold water is then pumped through a second heat exchanger which condenses the vapor to be recycled through the system.
The second cycle which is the open type uses the warm surface water to produce electricity. The warm ocean water is placed in a low-pressure container that causes it to boil. As the water boils, the turbines which are connected to the generator are turned. The cold water on the other hand, is used in condensation of the steam that has rid of its salts and other contaminants. This procedure is called desalination and it produces fresh potable water that is suitable for drinking and other uses.
Hybrid is the third type of cycle and from the name alone it is the combination of the open and the closed cycles. In the hybrid cycle the warm surface ocean water enters a vacuum chamber which is flash-evaporated. After which the vapor is used to vaporize the ammonia just like in the closed cycle and this turns the turbines to generate electricity. The steam then condenses in the heat exchanger and results to desalinated water just like in the open cycle.
Ocean thermal energy conversion together with the process of electrolysis can also produce enough hydrogen. Electrolysis is using direct electric current to facilitate a non-spontaneous chemical reaction. The generation of steam along with supplementary electrolyte compounds for efficiency improvement is a qualified medium for hydrogen production. Hydrogen produced can be used as fuel just like the other energy sources.
The ocean thermal energy conversion is not only used to produce electricity but it is also used for the purpose of air conditioning. The OTEC system which makes cold water available makes it possible for large area cooling in properties or projects near the plant. The cold water which has a temperature of 5 degrees Celsius or 41 degrees Fahrenheit is available to cool coils for building air conditioning. This is beneficial for businesses that need air conditioning for it only costs 5 to 10 cents per kilowatt-hour. This can help business owners to save in $200,000-$400,000 in energy bills. In fact, international hotels and businesses in Bora Bora like InterContinental and Thalasso Spa uses the OTEC system for air conditioning.
Another use for the ocean thermal energy conversion is agricultural chilled-soil. This is important for plants that grew in temperate weathers to survive in the subtropics. This happens when the cold-ocean water flows through underground pipes and chill the soil around the pipe. Dr. John P. Craven, Dr. Jack Davidson and Richard Bailey of the Natural Energy Laboratory of Hawaii Authority (NELHA) have patented this process. They have demonstrated that plants that could not normally survive in Keahole Point or in Hawaii did grow in the research facility.
Aside from this, the aquaculture is also benefited. High concentrations of needed nutrients are depleted in the surface waters because of biological consumption. With the OTEC system, the natural upsurge is simulated which is essential for the fertilization and sustaining of the marine ecosystems. Just like the idea of the chilled-agricultural soil, non-native water species can be cultivated in OTEC pools. Some of these species are salmon, lobsters, clams, trout, oysters and abalone. Not only does the ocean thermal energy conversion allow the great fresh seafood to be available in the market but it also helps in refrigeration.
However, the ocean thermal energy conversion also has its drawbacks. One of these is dissolved gasses. This happens in the intake pipe when the cold water rises and the pressures reduce at the point where the gas arises. Another disadvantage is called microbial fouling; a layer of this can be as thick as 25 to 50 centimeters. The thickness of it affects the performance of the heat exchangers adversely by almost 50 percent. This needs continuous removal in order to keep the performance of the heat exchangers at their peak. It was also found out that the sealing is hard and may cause a downside. The evaporator, turbine and the condenser needs to have a fractional vacuum of 3- 1 percent atmospheric pressure. The OTEC system must be prudently sealed in order to keep the operation from ceasing.
These are the components, advantages and the drawbacks that is present in the ocean thermal energy conversion. It is one of the green energy sources that are not yet used widely. From the year of 1880, there had been developments in this energy source. With the continuous study and dynamic technology, great possibilities of improvements on the OTEC process can be achieved in the future. Not only does it present many advantages but it also uses the natural power present in the ocean. Ocean thermal energy is indeed a green energy.