The Ocean Temperature Difference That Was Always There
Ocean thermal energy conversion exploits the temperature difference between warm surface water and cold deep ocean water to drive a thermodynamic cycle that produces electricity or provides cooling, using the ocean as a vast solar energy collector whose stored thermal energy creates the temperature differential that the OTEC system converts to useful energy. The physics of OTEC are straightforward: tropical ocean surface waters typically maintain temperatures between 25 and 28 degrees Celsius throughout the year, while water at depths between 800 and 1000 metres in the same locations maintains temperatures between 4 and 6 degrees Celsius, creating a temperature difference of 20 degrees or more that a Rankine cycle heat engine can operate between. The thermodynamic efficiency of a Rankine cycle operating between these temperatures is low, approximately 3 to 5 percent at best, reflecting the fundamental Carnot efficiency limitation of a small temperature difference heat engine, which is why OTEC has historically struggled to compete economically with other ocean energy sources whose energy density creates better power output per unit of infrastructure investment.
The commercial rediscovery of OTEC in the 2010s and 2020s has been driven not by improvements in the power generation economics that have constrained OTEC since its concept was first proposed by Jacques-Arsene d'Arsonval in 1881, but by the identification of seawater air conditioning as an OTEC-adjacent application whose commercial economics are substantially more favourable than power generation. Seawater air conditioning, which pumps cold deep ocean water through a heat exchanger that cools the chilled water circuit of a conventional air conditioning system without requiring the refrigeration compressor that conventional air conditioning's energy consumption is dominated by, can reduce the energy consumption of air conditioning by up to ninety percent relative to conventional electric compression refrigeration. In tropical island locations whose deep cold water is accessible within a few kilometres of coastal areas that require air conditioning cooling for hotels, resorts, data centres, and commercial buildings, the economics of seawater air conditioning can be commercially compelling even without any power generation from the temperature difference whose cold water extraction is the primary commercial driver.
Makai Ocean Engineering and the Hawaii Commercial Reference
Makai Ocean Engineering, a Hawaii-based ocean engineering company, operates the Natural Energy Laboratory of Hawaii Authority's 100 kilowatt OTEC facility at Keahole Point on the Big Island of Hawaii, which is the world's largest operational OTEC plant and the commercial reference installation for closed-cycle OTEC power generation using ammonia as the working fluid. The NELHA facility's cold seawater pipeline, which delivers 6 degree Celsius water from 600 to 900 metre depth to the onshore facility, provides the deep cold water resource that both the OTEC power generation demonstration and the seawater air conditioning system in the facility's aquaculture research buildings uses for cooling. Makai's research on heat exchanger fouling, pipe material corrosion, and working fluid selection for tropical OTEC conditions has produced the engineering knowledge base that commercial OTEC project development builds on, and its long-term operational experience with the NELHA cold seawater pipeline infrastructure has quantified the maintenance requirements and energy consumption of deep water pumping that determines the net energy output and economic performance of seawater air conditioning projects.
Honolulu's Seawater Air Conditioning project, a commercial seawater air conditioning system whose implementation by Makai and whose cold seawater supply from a dedicated deep water pipeline delivers cooling to commercial buildings in downtown Honolulu, represents the most commercially mature OTEC-derived seawater cooling deployment whose operational performance provides the economic validation that island resort developers, data centre operators, and coastal commercial building owners elsewhere in the tropical Pacific and Caribbean are evaluating for their own facility cooling needs. The replacement of conventional electric compression air conditioning with seawater cooling whose pumping energy is a fraction of the compression energy it replaces creates a cooling system whose operating cost reduction justifies the capital cost of the cold water pipeline and distribution system over the project's lifetime, with the financial case strengthened in island economies whose electricity prices are substantially higher than continental market averages because of the diesel generation dependency that grid connectivity to low-cost baseload generation cannot resolve.
The Island Economy Commercial Context
The commercial deployment of OTEC-derived seawater air conditioning is concentrated in tropical island economies whose combination of high electricity prices, abundant deep cold water access within feasible pipeline distances from coastal population centres, and high cooling demand from tourism, data centre, and commercial building air conditioning creates the commercial context where seawater cooling can compete economically with conventional air conditioning without the subsidy support that renewable power generation typically requires to compete with incumbent fossil generation. Pacific island nations, Caribbean islands, and coastal areas of tropical developing nations whose cooling energy burden is growing with economic development and whose electricity infrastructure is poorly positioned to absorb the load growth that increased air conditioning penetration creates present the commercial markets where seawater air conditioning projects are being evaluated and in some cases being developed.
Top 10 Companies in Ocean Thermal Energy Conversion and Seawater Cooling Globally
- Makai Ocean Engineering: US OTEC engineering company with the world's largest operational OTEC plant at NELHA Hawaii and the Honolulu Seawater Air Conditioning project; its OTEC heat exchanger technology, deep water pipeline engineering, and commercial seawater cooling system design create the reference OTEC engineering company whose commercial and research experience defines the practical OTEC knowledge base.
- Natural Energy Laboratory of Hawaii Authority: Hawaii state agency operating the deep seawater pipeline infrastructure at Keahole Point and providing cold seawater access to OTEC research and commercial tenants; its existing deep water infrastructure whose pipeline capital cost is amortised across multiple users creates the cost-sharing model that makes Hawaii the most commercially accessible OTEC development location globally.
- Ocean Thermal Energy Corporation: US OTEC project development company with commercial OTEC power and seawater cooling project development in Pacific islands and Caribbean markets; its OTEC project financing and development expertise and its island economy partnerships create the commercial OTEC project developer whose pipeline of projects demonstrates the market development beyond the Hawaii reference installation.
- Naval Group (DCNS): French naval and marine energy company with OTEC technology development including a 10.7 megawatt pilot plant project in Martinique; its French government support and its partnership with Akuo Energy for the Martinique OTEC project create the European OTEC commercial development programme whose French overseas territory context provides the island economy commercial setting and public financing support.
- Global OTEC Resources: UK OTEC project developer with projects in West Africa and Pacific island markets; its OTEC vessel concept that places the OTEC plant on a floating offshore structure rather than requiring the onshore pipeline infrastructure creates the alternative deployment model for locations where coastal geography makes onshore pipeline installation impractical.
- Xenesys: Japanese OTEC component manufacturer with heat exchangers and system components for OTEC applications; its titanium plate heat exchanger technology optimised for the small temperature difference and large flow rate conditions of OTEC operation and its collaboration with Japanese government OTEC research programmes create the OTEC component supply infrastructure.
- IHI Corporation: Japanese heavy engineering company with OTEC power plant development for Pacific island applications; its engineering capability for large marine energy infrastructure and its Japanese government ocean energy development programme participation create the Japanese industrial company's OTEC commercial development position.
- Honolulu Seawater Air Conditioning (Vicinity Energy): US seawater cooling company operating the Honolulu downtown district cooling system using deep Pacific Ocean cold water; its commercial operation serving Honolulu's central business district commercial buildings creates the US commercial seawater air conditioning reference whose energy savings and operational performance data inform seawater cooling feasibility assessments globally.
- Blue21: Dutch floating city and ocean energy company with OTEC integration into floating urban development concepts; its engineering of OTEC into the thermal management of floating community structures creates the architectural integration of ocean thermal energy that differs from the conventional coastal pipeline approach and addresses the urban development context for tropical ocean regions.
- Akuo Energy: French renewable energy developer with OTEC project co-development in Martinique with Naval Group; its renewable energy project development expertise and its French overseas territory regulatory relationships create the energy developer partner whose project financing and permitting capability enables OTEC technology commercialisation beyond the engineering stage that pure technology companies cannot sustain.