What is ocean thermal energy?

Ocean Thermal Energy or Ocean Thermal Energy Conversion (OTEC) is a procedure that generates electricity by the usage of the temperature difference between the deep-freezing ocean or sea cold water and the shore-based tropical warm surface water. The OTEC plant pumps extensive quantities of deep-freezing ocean cold water, and warm surface seawater that is obligatory to run a power cycle and create electricity. OTEC is a (24/7) power initiating firm, a sustainable energy source and capable of supplying enormous levels of energy.

In tropical island communities, where most of the electricity production is oil-based. factors such as high electricity costs, increase in global warming, extensive renewable energy usage, and political devotion to energy security have made OTEC commercialization economically appealing. This island market is huge in the US and massive globally.

The U.S. Department as center for Ocean Thermal Energy Conversion

The Ocean Energy Research Center (OERC) in Hawaii, USA is a distinctive and important research facility committed to displaying and improving technology to harness the ocean thermal renewable energy conversion. The main focus is on OTEC systems, but research is in process at the Center to support other deep seawater technologies, inclusive of:

• Seawater Air Conditioning (SWAC)
• Marine heat exchanger for different applications
• Marine Corrosion Research

The OERC is the sole research facility with constant access to shallow and deep seawater. A turbine generator has been attached to complete the OERC’s land-based OTEC plant for supplying closed-cycle OTEC power for the very first time in the history of the United States.

Types and working of OTEC power cycles

Deep-Ocean water is an essential part of these three types of OTEC systems that are closed-cycle system, open-cycle system, and hybrid system. To function, the cold sea or water must be driven to the surface. The foremost techniques are active pumping and desalination. Desalination of this water near the floor of the sea lowers the density, which results in the rise of seawater to the surface.

Closed cycle system

Closed-cycle Ocean Thermal Energy Conversion (OTEC) system use low-boiling point fluids, like ammonia to give energy to the turbine for the production of electricity. The sun-warmed surface seawater is pumped through a heat exchanger for fluid vaporization. The expanding of vapor turns the turbo generator by giving power, the cold water which is being pumped through another heat exchanger that condenses the vapor into a liquid matter and is then recycled through the system.

In 1979, the Natural Energy Laboratory and various corporate-sector partners made the ‘Mini-OTEC’ experiment, the primary successful development at the sea production of net electric power from closed-cycle OTEC system. The Mini-OTEC vessel was fastened 2.4 km off the Hawaiian coast that generated adequate electricity to illuminate the whole ship.

Open cycle system

The Open-cycle Ocean Thermal Energy Conversion (OTEC) system uses the warm surface water directly to create electricity. The warm seawater is first pumped into a low-pressure vessel where it boils. The salt left behind by the vapors and other contaminants in the vessel is pure. It is then condensed into a liquid by exposing it to the cold temperature difference from deep-ocean cold water.

In 1984, the National Energy Laboratory made a vertical-spout evaporator to change warm seawater into low-pressure steam for open-cycle plants making the proper use of ocean-based renewable energy. In 1993, an open-cycle OTEC plant in Hawaii broke the record of 40 kW electricity production by the Japanese system and generated nearly 80 kW of electricity.

Hybrid cycle system

A hybrid cycle Ocean Thermal Energy Conversion (OTEC) system is the amalgamation of the features of the closed and open-cycle systems. . Here, the warm seawater breaks into a vacuum space and is flash-evaporated, similar to the open-cycle evaporation process. The steam produced vaporizes the ammonia and then directs the liquid of a closed-cycle loop to the further side of the ammonia vaporizer. The vaporized fluid then powers the turbine to give electricity. The steam condenses inside the heat exchanger and supplies desalinated distilled water.

Future of the OERC

Makai’s Ocean Energy Research Center which is under the jurisdiction of Makai Ocean Engineering will continue to serve as the elite testbed for the Ocean Thermal Energy Conversion (OTEC) technology. The land-based OTEC plant operation by Makai Ocean Engineering will deliver crucial knowledge and expertise for the next goal in OTEC. The OTEC plant has the caliber to offer an abundance of energy according to global requirements that are 10 to 100 times greater than various ocean energy options, unlike previous Ocean Thermal Energy Conversion (OTEC) systems that were 1% to 3% efficient thermally. The Ocean Thermal Energy Conversion OTEC plant can operate without stopping to provide a base-load supply for electric power generation. The main technical challenge of the OTEC plant is to produce that required quantity of power seamlessly from a small temperature difference.

For climate control, the ocean thermal gradient is useful to increase rainfall, maintain the temperature difference and balance the high temperatures in the tropical areas which is advantageous for us and the surroundings along with extensive use of renewable sources.

Recent Developments

The Thalasso-Spa on the Bora Bora Island has installed a SWAC air conditioning system for the buildings in the vicinity. It passes seawater through a heat exchanger where the freshwater cools down in a closed-loop system and then This cold water is then pumped to the buildings that directly cools the air.

In late 2016, Makai completed the installation of the innovative equipment for the rapid prototyping and manufacture of heat exchangers at our OERC on the Natural Energy Lab of Hawaii Authority (NELHA) campus. This new, state-of-the-art facility features advanced technology manufacturing equipment for the production in the fabrication of advanced heat exchanger designs.

Since 2008, habitat considerations, renewable energy application, and the new Department of the navy energy policy led to the support to improve the OTEC technologies.

Context and Applications

The topic is taught in courses related to:

• Bachelors of Technology (Civil Engineering)
• Masters in Science (Ocean and Marine Engineering)
• Masters of Technology (Hydraulics Engineering)
• Masters in Science (Environmental Engineering)

Practice Problems

Q1. The full form of OTEC is?

1. Ocean Tropical Energy Conversion
2. Ocean Thermal Energy Conversion
3. Ocean Thermal Electric Conservation
4. Ocean Tropical Electric Conversion

Correct Option: b

Explanation: The full-form of OTEC is Ocean Thermal Energy Conversion.

Q2. The Mini OTCE vessel was installed at what distance off the Hawaiian coast for giving electricity to the ship using ocean renewable energy?

1. 2.1 km
2. 2.2 km
3. 2.3 km
4. 2.4 km

Correct Option: d

Explanation: The Mini OTCE vessel was installed at 2.4 km off the Hawaiian coast for giving electricity to the ship.

Q3. In 1993, the National Energy Laboratory broke the record of the Japanese open-cycle OTEC plant system to produce how much (kW) of power in total?

1. 40 kW
2. 60 kW
3. 80 kW
4. 100 kW

Correct Option: c

Explanation: In 1993, the National Energy Laboratory broke the record of the Japanese open-cycle OTEC plant system to produce 80 kW of power in total.

Q4. Makai completed the installation of innovative equipment for the rapid prototyping and manufacture of heat exchangers at our OERC on which campus?

1. Natural Energy Lab of Hawaii Authority
2. National Energy Lab of Hawaii Authority
3. Natural Electric Lab of Hawaii Authority
4. National Electric Lab of Hawaii Authority

Correct Option: a

Explanation: Makai completed the installation of innovative equipment for the rapid prototyping and manufacture of heat exchangers at our OERC on the Natural Energy Lab of Hawaii Authority (NELHA) campus.

Q5. What is the full form of OERC?

1. Ocean Energy Research Center
2. Organic Electric Research Center
3. Ocean Energy Redevelopment Center
4. Organic Electric Redevelopment Center

Correct Option: a

Explanation: The full-form of OERC is Ocean Energy Research Center.

Related Concepts

• Fluid mechanics
• Hydraulics
• Water resource engineering
• Naval architecture and marine Studies