OTEC: Generating Electricity From Seawater By Exploiting Temperature Differences

The process of converting ocean thermal energy into electrical energy is called ‘Ocean Thermal Energy Conversion’ (Ocean Thermal Energy Conversion), which is abbreviated as ‘OTEC’ or ‘Otec’.

In this groundbreaking technology, it is possible to use the difference in temperature of sea water to produce infinite energy.

Also, this method does not require the use of any fossil fuel. As a result, the damage to the environment is also less. Compared to other methods of power generation, OTEC is cost-effective, environmentally friendly and reliable at the same time. Also electricity can be produced easily in this technology.

History Of Otech

In 1881, French physicist Jacques Arsene Darsonval first proposed the idea of ​​harnessing the thermal energy of the ocean.

He came up with the idea of ​​generating electricity through a closed-cycle system. Most of today’s Otech plants are built according to the method he invented. This process basically uses a substance like dissolved ammonia as a refrigerant.

During the 1970s and 1980s, several countries, including the United States and Japan, began experimenting with the potential of OTEC technology. Their aim was to invent a source of renewable and sustainable energy.

Researchers in the United States were able to build the first Otech plant capable of generating substantial amounts of electricity. About 15 kilowatts of electricity was produced from that plant named ‘Mini Otech’ which was launched in 1979. The plant was installed on several US ships a few kilometers off the island of Hawaii. The plant was built on a closed-cycle system.

In 1981-82, a number of Japanese businesses jointly built another Otech plant on an experimental basis. This plant was also based on Badha-Chakra or ‘Closed-Cycle System’.

The plant was located on the island of Nauru in the Pacific Ocean. A total of 35 KW of electricity could be generated from this plant.

By 1999, a 250 kW Otech plant on the island of Hawaii was successfully generating electricity.

Since then, researchers have been working on how to improve this technology. For this reason, various researches are being conducted to improve the device called ‘heat exchanger’. Also research is being done on different ways to protect Otech plant equipment from sea salt water.

How This Technology Works

Otech technology requires variations in seawater temperature to work. Basically, this technology generates electricity by exploiting the temperature difference between the warm sea surface water and the cold water of the deep sea.

In tropical or subtropical climates, the temperature difference between sea surface and deep ocean water can be as much as 20 degrees Celsius or 68 degrees Fahrenheit. But usually this difference is between 6-12 degrees Celsius or 11-22 degrees Fahrenheit.

The basic idea behind this technology is to use hot sea surface water to vaporize a second liquid. The steam is then driven through a turbine to generate electricity. The steam is then cooled and condensed with cold water, and the cycle begins again.

There are basically 3 methods or ‘power cycles’ used to generate power through OTEC. These 3 cycles are Badha Chakra or Closed Cycle, Mukta Chakra or Open Cycle and Hybrid Cycle.

Closed Cycle

A liquid like ammonia is used as a refrigerant in this method. This liquid is evaporated using hot water.

The steam is then driven into a turbine to produce electricity through a generator. This vapor condenses in cooling water and turns into a liquid. Then the whole process starts again.

The biggest advantage of this method is that this plant can be installed in any environment. In this way, just as plants can be set up on land, floating plants can also be built in the sea.

Mukta Chakra Or Open Cycle

In this cycle, hot sea water is used to generate steam directly. The steam is then driven through a turbine to produce electricity with the help of a generator. The vapor is then cooled by contact with cold water and liquefied again.

A major advantage of this method is that it is very easy to make otech plant in this method and it does not require any secondary liquid.

However, this method will only work in tropical or subtropical climates where there is a large temperature difference between warm and cold water in the ocean.

Hybrid Bicycle

Hybrid cycles utilize the advantageous aspects of both closed and free cycles or systems.

In hybrid systems, refrigerants such as ammonia are vaporized using hot water. The generated steam drives the turbine to produce electricity with the help of a generator.

Now that steam is condensed with cold water. Some of the condensed steam formed here is used to re-evaporate the refrigerant. And the rest of the steam is driven into a second turbine, through which electricity is again generated.

Compared to the other two cycles, this method can produce electricity more efficiently.

Places Where Otech Plants Can Be Built

Otech plants can be constructed in 3 types of locations based on location. On land, floating in the sea or in the mesopan region.

Land-based otech plants are usually located near deep water sources in coastal areas. And the Otech plant located on the continental shelf or Mahisopan is called a ‘shelf-based plant’. Basically, the underwater land that gradually slopes down towards the sea is called Mahisopan in the language of geography.

And floating otech plants are usually built in tropical or subtropical climates.

Environmental Risk

However, this method of power generation has some environmental risks. For example:

• Impact on marine life: Hot water taken from the ocean can have negative effects on marine life. In particular, shallow-sea animals may have problems sustaining their lives.

• Risk of spillage of fuel oil into the ocean: Mineral oil is used as raw material in many plants. Accidental spillage of this oil into sea water can cause serious environmental damage.

• Ocean temperature balance may be disturbed: Extraction of large amounts of cold water from the deep ocean may disturb the temperature balance of ocean water. As a result, there is a risk of damaging the global climate.

• Building otech plants on a large scale becomes quite expensive. And building such a plant requires a lot of land and sea area.

Advantages Of Otec

Generating electricity using this technology does not produce any greenhouse gas or any other pollution. And from a huge source like the ocean, endless electricity can be produced in this way.

Otech plants can be built to meet the needs of any size community, from a small island to a large city. Without electricity, it is possible to produce fresh water from sea salt water in this method.

Also, since the temperature difference of sea water does not fluctuate much, otech is a reliable source of electricity generation.

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