Ocean Thermal Energy Conversion (OTEC)
Ocean Thermal Energy Conversion (OTEC) is a renewable energy technology that produces electricity using the natural temperature difference between warm surface seawater and cold deep seawater. This thermal gradient is strongest in tropical ocean regions and can be used to drive a thermodynamic cycle that generates clean, reliable power. Unlike intermittent wind or solar resources, OTEC provides continuous baseload energy and operates independently of weather conditions.
Growing demand for energy security and low-carbon electricity has renewed interest in this technology. OTEC is especially well-suited for island grids and remote coastal regions that rely on imported fossil fuels and face some of the world’s highest electricity costs. As system efficiencies continue to improve and deployment costs decline, OTEC is emerging as a long-term solution for sustainable ocean-based power generation.
How OTEC Works
Most modern OTEC systems use a closed-cycle configuration. In this design, warm seawater from the surface is used to heat a working fluid, typically ammonia, which has a low boiling point. The vapor produced drives a turbine connected to an electric generator. Cold seawater pumped from depths of approximately 1,000 meters condenses the vapor back into liquid form, allowing the process to repeat continuously.
Because the ocean provides a stable and constant temperature difference in tropical regions, OTEC can operate 24 hours a day, delivering steady power output to the electrical grid.
Advancing OTEC for More Than Four Decades
Makai has been advancing OTEC technology since 1979, beginning with its contributions to the world’s first net-power producing OTEC plant. Over the past four decades, Makai has executed engineering programs across every major component of OTEC systems, including heat exchangers, offshore pipelines, control systems, and platform integration.
The company has served as both a prime contractor and a key engineering partner for dozens of OTEC research and development initiatives. Makai has supported major industry programs with organizations such as Lockheed Martin, the U.S. Department of Energy, the Office of Naval Research (ONR), and NAVFAC to assess and design commercial-scale systems, including 100 MW-class configurations for island grids. Makai also designed and operates the largest grid-connected OTEC facility in the United States at the Natural Energy Laboratory of Hawaii Authority (NELHA).
OTEC Engineering Services
Makai provides complete engineering support for the development of reliable, scalable Ocean Thermal Energy Conversion (OTEC) systems. With more than four decades of deep seawater system experience, Makai delivers practical, technically sound solutions that reduce cost and risk from early-stage studies through commercial implementation.
OTEC System Design & Analysis
- OTEC system architecture
- Working fluid analysis and power cycle optimization
- Turbine and heat exchanger integration
- Balance-of-plant (BOP) system design
- Performance modeling and thermodynamic efficiency analysis
Heat Exchanger Innovation
- Thin Foil Heat Exchanger (TFHX) design and testing
- High-performance evaporator and condenser development
- Anti-fouling strategies and long-term reliability assessment
- Corrosion mitigation engineering for marine environments
Cold Water Pipe (CWP) Engineering
- Large-diameter offshore pipeline design (HDPE and composite)
- Seabed routing, stability, and dynamic loading analysis
- Fatigue and stress assessment of deep-water intakes
- Installation planning and offshore deployment engineering
Offshore Platform & Subsea Systems
- Floating OTEC platform design
- Mooring and station-keeping analysis
- Subsea cable routing and installation engineering
- Intake and discharge diffuser design
- Marine construction engineering support
Project Feasibility & Development
- Site selection and resource assessment
- Ocean thermal gradient and intake location studies
- Techno-economic analysis and LCOE modeling
- Commercial deployment strategies for island grids
- Cost reduction strategies and phased implementation planning
Download OTEC Capability Overview
Learn more about Makai’s OTEC engineering experience and technical capabilities. This brochure provides a summary of some of our past performance, design expertise, and project history in Ocean Thermal Energy Conversion.
Benefits and Opportunities
Immense Resource
OTEC is solar power, using the oceans as a thermal storage system for 24-hour production. Unlike other renewable energies, the maximum available energy is not limited by land, shorelines, water, environmental impact, human impact, etc.
Baseload Power
OTEC is dispatchable, meaning that its power can be ramped up and down quickly (in a matter of seconds) to compensate for fluctuating power demand or supply from intermittent renewables. For this reason, this technology is complementary to other renewables like solar and wind, and could enable further penetration on the grid while helping to maintain its stability.
Security
Offers the opportunity of tapping an immense energy resource that is not controlled by other nations.
Renewable
Believed to be sustainable at four or more times current total global electrical energy production.
Low Risk
Conventional Closed Cycle OTEC is a low-risk.
Clean Energy
Has the potential of being a very clean alternative energy – unique for a firm power source capable of providing massive energy needs. The environmental risk is very low.
Offshore
Production occurs offshore. Land resources are not needed other than for on-shore landing. Not competing for other vital resources such as food and fresh water.
Challenges
The primary challenge for this form of ocean energy has always been cost. Commercial deployment has lagged because early system designs required very large facilities to be competitive. For years, it was assumed that a plant needed to be on the order of 100 MW to achieve economic viability, which made first-of-a-kind investment difficult.
Recent engineering advancements are changing that outlook. Makai’s development of high-performance heat exchangers—particularly the Thin Foil Heat Exchanger (TFHX)—has significantly improved system efficiency and reduced capital costs. These improvements suggest that commercially viable plants could now be achievable at capacities as low as 10 MW in select locations.
At today’s energy prices, this technology is already competitive for island grids with high electricity costs, such as Hawaii, Guam, and Puerto Rico. In a study for the Office of Naval Research, Makai also evaluated large offshore facilities that would export energy to the continental United States using ammonia as a transportable energy carrier. While projected costs remain slightly above some renewables, the gap is narrowing and is within reach as engineering and manufacturing scale improve.
Related Technologies
Makai’s engineering team has deep expertise in the enabling systems required for Ocean Thermal Energy Conversion, including large-diameter deep seawater pipelines and high-efficiency heat exchangers. The company is also a recognized leader in Seawater Air Conditioning (SWAC), a related deep-ocean technology that uses the same cold seawater resource to provide renewable district cooling. This complementary experience has made Makai one of the most capable organizations in the world at designing and delivering deep seawater infrastructure.
Ocean Energy Research Center
The Ocean Energy Research Center (OERC) in Kailua-Kona, Hawaii, is a dedicated test facility for advancing technologies that utilize the thermal and physical properties of deep ocean water. While its primary focus is the development and demonstration of Ocean Thermal Energy Conversion (OTEC) systems, the facility also supports related research areas, including:
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- Seawater Air Conditioning (SWAC)
- Marine heat exchanger development
- Marine Corrosion Research.
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The OERC is one of the only facilities in the world with continuous access to both shallow and deep seawater at utility-scale flow rates, making it a critical asset for applied ocean energy research. In 2015, a turbine-generator was installed to complete a land-based OTEC demonstration system at the site, supplying power to the Hawaiian grid, making it the first closed-cycle OTEC electricity ever delivered to a U.S. utility.
OTEC Grid-connection Ceremony
In August 2015, Makai installed a 105 kW turbine-generator at the OERC, creating the world’s largest grid-connected OTEC power plant. This system serves as a critical platform for advancing commercial-scale development. Its objectives include:
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- Testing and refinement of power control and automation systems
- Measuring actual versus predicted power output to validate performance models
- Collecting long-term operating data to improve future plant designs and reduce levelized cost of energy (LCOE)
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Makai’s Projects
With over four decades of focused development, Makai has played a central role in the evolution of OTEC technology, from early research to modern utility-scale development efforts. Key projects include:
105 kW Pilot Plant
In 2015, Makai connected closed-cycle OTEC power to the U.S. grid for the first time. This project provided significant de-risking of the technology and proved its viability as a U.S. energy provider.
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This facility is used for the research and development of heat exchangers, the turbine-generator and system controls, corrosion resistant materials and bonding methods, and marine pipelines. The developments resulting from each of these areas are ultimately fed into more cost-effective and technically advanced OTEC power plant designs.
Hawaii – 1 m Pipe Repair
In 2011, Makai performed final design and construction oversight for the repair of a deepwater 40” (1.0 m) diameter HDPE pipe at the Natural Energy Laboratory of Hawaii (NELHA).
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This pipe is a main source of water at NELHA and supplied all of the water for Makai’s 105 kW closed-cycle OTEC power plant. The pipe, originally built for ten year design life, has been in place for over 25 years. The pipe design involves a 915m long floating catenary section from 150m to 670m depth, and several of the chain bridles restraining the pipe had worn from corrosion and continuous motion over the years. Makai simulated the current pipe conditions using Orcaflex 3-dimensional finite element software, simulated repair solutions, and provided final design drawings and specifications. In July 2013, repairs were conducted and Makai provided on-site representation for our client, the State of Hawaii. The repairs were successful, and post-repair measurements showed excellent agreement with Makai’s model predictions and design specifications.
HOST Park Deep Seawater Pipeline
In 2001, Makai engineered the main seawater supply source for the Hawaii Ocean Science Technology Park (HOST Park). This included a cold-water pipeline 55″ diameter, 3000′ deep, and two miles long.
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Makai has engineered the main seawater supply source for the Hawaii Ocean Science Technology Park (HOST Park) at Keahole Point, Hawaii. This supply system consists of a cold-water pipeline (55″ diameter, 3000′ deep, and two miles long), a 55″ diameter warm water intake pipe, a tunneled shoreline crossing, and a shore-based pumping station. The system is the world’s largest and deepest cold-water pipeline and has the capacity to deliver 27,000 gpm of 4 deg. C. water and over 40,000 gpm of warm water to the technology park. Makai received a national award from the American Society of Civil Engineers for this project as one of the six most outstanding CE projects in 2003.
Indian OTEC Pipeline
In 1998, Makai provided conceptual designs and design guidance for an OTEC intake pipeline and mooring system in India.
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Makai was contracted by the National Institute of Ocean Technology (NIOT) in Madras, India, for the conceptual design of the deep water intake pipeline, the effluent pipeline, and the mooring system for an experimental floating OTEC Plant. The analysis included dynamic modeling of pipe bending, shown at right.
The NIOT barge was planned to be 72 meters long and would supply 1415 kg/s of deep cold seawater through a 1 meter diameter pipeline from a minimum depth of 1000 meters. The mooring was expected to be 1220 meters deep.
NELHA 40″ Cold Ocean Water Intake Pipeline
In 1987, a project funded by the State of Hawaii and the U.S. Department of Energy, Makai designed a 40″ polyethylene cold water pipe to be used jointly by the Natural Energy Laboratory and the Hawaii Ocean Science and Technology (HOST) Park sites on the Big Island. At the time of construction, it was the largest deep-water intake pipeline in the world. This pipe is a main source of water at NELHA and supplied all of the water for Makai’s 105 kW closed-cycle OTEC power plant.
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This pipe is a larger and more rugged version of the previous MOE 12″ pipe design at NELHA and includes a 3000′ long buoyant section. Makai assisted in the deployment of this pipe to a depth of 2200′ in August 1987.
NELHA 18″ Cold Water Pipeline
In 1987, Makai designed and provided construction management for an 18″ down-the-slope cold water intake at the Natural Energy Laboratory of Hawaii.
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The goal was to install a reliable, minimal cost, deep-water intake system to 2000′. This polyethylene design differs from previous NELHA pipelines in that the deep water pipe is buoyed approximately 40′ off the bottom on a series of pendants, the deployment was accomplished without major offshore equipment. This pipeline was successfully deployed in October, 1987, and is still operational.
OTEC Pipeline Research
In 1984 Makai was responsible for the concept development, design and deployment planning for an 8′ diameter down-the-slope OTEC pipe test.
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Working under a subcontract to Hawaiian Dredging and Construction, on a NOAA/DOE program, Makai was responsible for the concept development, design and deployment planning for an 8′ diameter down-the-slope OTEC pipe test. Part of the test was the demonstration of diver-free installation techniques suitable for very deep, large diameter pipelines on the steep, 42 degree slope. The concept included a flexible pipe joint that conformed to the bathymetry. Pipe deployment was successfully accomplished as planned using heavy lift barges and closed-circuit underwater television. The design included instrumentation for the measurement of hydrodynamic loads on the pipe after installation. Makai subsequently analyzed the hydrodynamic data from this test project.
Long Operating OTEC Pipeline
In 1981, Makai conceived, designed and managed the construction of an experimental, polyethylene OTEC pipeline, 12″ in diameter, for the State of Hawaii.
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This one-mile long pipeline has an intake at 2000′ and utilizes a unique 3000′ long free-floating catenary section to avoid contact with the steep, rocky bottom. The pipeline was installed in 1981 off Keahole Point, Hawaii. In spite of its “temporary” design life of 2 years, it has survived many major storms including a hurricane and was operational for over twelve years.
Mini OTEC
In 1979 Makai engineered several portions of the Mini-OTEC project under contract to Dillingham Corp. This was a full system demonstration.
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This project was a full demonstration of Ocean Thermal Energy Conversion and jointly funded by the State of Hawaii, Lockheed, Dillingham and Alfa Laval. Makai designed a 2′ diameter polyethylene pipe that served not only as an intake pipe from a 2000′ depth, but also as the “mooring line” for the 120′ x 35′ barge. The initial design for the barge layout, seawater intakes (cold and warm), effluent lines, and pumps was also done by Makai. Makai developed and planned the deployment scheme and participated in the at¬sea deployment. On August 2, 1979, Mini¬OTEC produced 50 kW of power and consumed 40 kW, for a net positive output of 10 kW. This was the first time that a positive output had been achieved from any OTEC facility. In 1980, the National Society of Professional Engineers awarded Mini-OTEC as being one of the ten outstanding engineering achievements in the United States that year.
Global OTEC Applications
Ocean Thermal Energy Conversion is best suited for regions where deep, cold seawater is close to shore and warm surface water provides a strong temperature gradient. These conditions are found in tropical and subtropical regions around the world, creating significant potential for energy development.
Ideal locations for deployment include:
Island energy grids
Hawaii, Guam, Puerto Rico, U.S. Virgin Islands, Maldives, Mauritius, and Pacific Island nations can benefit from local renewable energy production and reduced fuel imports.
Coastal nations with deep offshore resources
Japan, Indonesia, the Philippines, Papua New Guinea, and parts of the Indian Ocean region have favorable conditions for OTEC development.
Defense and energy security applications
Remote bases and mission-critical operations, particularly those operated by the U.S. Department of Defense, can use OTEC to improve resilience and reduce logistical fuel requirements.
Offshore energy and industrial development
OTEC can co-locate with offshore data centers, hydrogen/ammonia production facilities, and seawater district cooling (SWAC) systems to provide integrated energy solutions.
OTEC Frequently Asked Questions
What is Ocean Thermal Energy Conversion (OTEC)?
It is a renewable power technology that generates electricity using the temperature difference between warm surface seawater and cold deep seawater. Because the ocean temperature gradient is constant in tropical regions, it can generate continuous, stable energy.
How does a closed-cycle system work?
In closed-cycle plants, warm seawater is used to vaporize a working fluid with a low boiling point, such as ammonia. The vapor drives a turbine to produce electricity. Cold seawater from depth is then used to condense the vapor back into liquid form to repeat the cycle.
What are the advantages compared to wind and solar?
Unlike wind and solar energy, this method provides round-the-clock power and does not require energy storage. It also supports additional applications such as seawater district cooling, desalination, and hydrogen or ammonia production.
Where can this technology be used?
It performs best in tropical and subtropical regions where deep cold seawater is close to shore. Ideal locations include Hawaii, Guam, Puerto Rico, the Caribbean, Southeast Asia, and other island and coastal regions.
Is it commercially viable today?
Commercial-scale plants have not yet been built, but recent engineering advancements are reducing cost barriers. Improvements in heat exchanger efficiency, offshore pipeline design, and modular construction are making deployment at smaller scales increasingly practical. Early commercial systems are expected in high-energy-cost regions first, with wider adoption as costs decrease through continued development.
What role does Makai play in OTEC development?
Makai has been actively developing this technology for more than 40 years through system design, thermodynamic modeling, offshore pipeline engineering, and heat exchanger innovation. The company designed and operates the largest grid-connected demonstration plant of its kind in the United States and provides engineering support for feasibility studies and early-stage commercial projects worldwide.
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