Ocean Thermal Energy Conversion Plant Research Articles

Global warming, a global energy resource

Global warming is a thermodynamics problem. When excess heat is added to the climate system, the land warms more quickly than the oceans due to the land’s reduced heat capacity. The oceans have a greater heat capacity because of its higher specific heat and the heat mixing in the upper layer of the ocean. Thermodynamic Geoengineering (TG) is a global cooling method which deployed at scale would generate 1.6 times the world’s current supply of primary energy and remove carbon dioxide (CO2) from the atmosphere. The cooling would mirror the ostensible 2008–2013 global warming hiatus. At scale 31,000 1-gigawatt (GW) ocean thermal energy conversion (OTEC) plants are estimated to be able to: a) displace about 0.8 watts per square meter (W/m2) of average global surface heat from the surface of the ocean to deep water that could be recycled in 226-year cycles, b) produce 31 terawatts (TW) (relative to 2019 global use of 19.2 TW and c) absorb about 4.3 Gt CO2 per year from the atmosphere by cooling the surface. The estimated cost of these plants is $2.1 trillion per year or 30 years to ramp up to 31,000 plants which are replaced as needed thereafter. Compared for example to the cost of world oil consumption that in 2019 was $2.3 trillion for 11.6 TW. The cost of the energy generated is estimated at $0.008/KWh.

Thermodynamic, economic, exergoeconomic analysis of an integrated ocean thermal energy conversion system

This paper proposes an integrated ocean thermal energy conversion (OTEC) system that couples power generation, refrigeration, and desalination. Based on the mathematical model, the thermodynamic, economic, and exergoeconomic performances are explored by evaluating several crucial parameters such as the ammonia-water concentration of the power subsystem (Xgen), the turbine inlet pressure (Pturb), etc. The results indicate that integrated OTEC system significantly improve the exergoeconomic performance since the efficient utilization of the exhausted cold seawater. The integrated system can achieve maximum net output power of 16.79 kW, refrigeration capacity of 268.87 kW, freshwater production of 53.22 t/d, as well as exergetic efficiency of 31.69% when the power subsystem's flow rate is 1.0 kg/s. Moreover, there is a maximum net output power when Pturb is under 800 kPa, and increasing Pturb leads to higher optimal Xgen. The maximum net output power, for instance, is 2.18 kW, 4.62 kW, and 9.79 kW when Pturb value is 600 kPa, 700 kPa, and 800 kPa, respectively, with corresponding optimal ammonia concentration values of 0.73, 0.83, 0.93. Furthermore, the maximum exergetic efficiency increases as Pturb enlarges. The maximum exergetic efficiency rises from 20.40% to 31.69% when Pturb increases from 600 kPa to 950 kPa. Besides, compared to the single OTEC plant's levelized cost of energy at 3.56 $/(kWh), the integrated system's can be as low as 0.098 $/(kWh).

Energy and economic analysis of an ocean thermal energy conversion plant for Bangladesh: A case study

Bangladesh's surging power demand, especially in coastal regions and nearby islands, necessitates a shift towards sustainable energy sources to meet Sustainable Development Goal 7 (SDG-7) objectives. This research attempts to visualize the ocean thermal energy reserves of the Bay of Bengal, with an extended focus on the marine borders of Bangladesh using advanced data analytics. Extensive data used is from a hybrid ocean coordinate model, Hybrid Coordinate Ocean Model and Navy Coupled Ocean Data Assimilation (HYCOM + NCODA) at 1/12° resolution, which has proven to be sophisticated and precise in providing oceanic information. Analyzing the data shows that geographically Bangladesh is feasible for Ocean Thermal Energy Conversion (OTEC) plants. A model plant is implemented at the potential location, and a Machine Learning (ML) model is trained to forecast temperature values for the future lifetime of the plant. ML forecasted results show the annual average power generated varies between 103.8 and 105.8 MW throughout the plant's life. However, a slight downward trend in generated power is observed, possibly due to climate change. The Levelized Cost of Electricity (LCOE) is calculated at 0.164 USD/kW, with an 11-year payback period. Notably, the plant registers zero Greenhouse Gas (GHG) emissions, aligning with Bangladesh's SDG-13 targets.

The global techno-economic potential of floating, closed-cycle ocean thermal energy conversion

Ocean Thermal Energy Conversion (OTEC) is an emerging renewable energy technology using the ocean’s heat to produce electricity. Given its early development stage, OTEC’s economics are still uncertain and there is no global assessment of its economic potential, yet. Here, we present the model pyOTEC that designs OTEC plants for best economic performance considering the spatiotemporally specific availability and seasonality of ocean thermal energy resources. We apply pyOTEC to more than 100 regions with technically feasible sites to obtain an order-of-magnitude estimation of OTEC’s global technical and economic potential. We find that OTEC’s global technical potential of 107 PWh/year could cover 11 PWh of 2019 electricity demand. At ≥ 120 MWgross, there are OTEC plants with Levelised Cost of Electricity (LCOE) below 15 US¢(2021)/kWh in 15 regions, including China, Brazil, and Indonesia. In the short-to-medium term, however, small island developing states are OTEC’s most relevant niche. Systems below 10 MWgross could fully and cost-effectively substitute Diesel generators on islands where that is more challenging with other renewables. With the global analysis, we also corroborate that most OTEC plants return the best economic performance if designed for worst-case surface and deep-sea water temperatures, which we further back up with a sensitivity analysis. We lay out pyOTEC’s limitations and fields for development to expand and refine our findings. The model as well as key data per region are publically accessible online.

Effect of Sea Current to Composites Cold Water Pipeline of Ocean Thermal Energy Conversion in Indonesia

Ocean thermal energy conversion (OTEC) is a new source of future energy that is clean and environmentally friendly with zero emissions. It is very potential to be developed in Indonesia, which is located at the equator. to meet the electricity needs of the outermost and remote islands that are not currently covered by the main power plants in Indonesia. Indonesia has deep seas around the islands with temperatures of 5°C and surface temperatures above 25-28°C, so a temperature difference of 20°C can be obtained easily for OTEC power plants. Cold water supplied to the OTEC plant with a capacity of 2 MW at sea level requires a pipe with a diameter of 4 m and a length of 500 m. The pipeline must be insulating, not floating, corrosion-resistant, and resistant to current loads. Current is a very serious concern with the potential to cause pipe failure. The pipe material being investigated is a short fiberglass High-density polyethylene composite. In this study, a simulation of the effect of current on the composite pipe was carried out to obtain an overview of the stress that occurs and the proper pipe dimensions used. The highest current speed in Indonesian water is found in the Makassar Strait from July to September at 0.8 m/s at a depth of 100 m. Based on the OTEC Pro Simulation software for a capacity of 2 MW, resulted in the pipe size is 4 m and the pipe length is 500 m which refers to the temperature profile. In the simulation, the calculation of the dynamically moving current becomes the drag force on the pipe, and with the Autodesk inventor, it is known that the deflection in the pipe, and the yield stress cause failure in the pipe. Subsequently, from the deflection and yield stress data, a pipe thickness of 20-30 cm is obtained for the short fiberglass-HDPE composite material which is safe to use as an OTEC cold water pipe with a capacity of 2 MW. Pipes with a thickness smaller than 15 cm are too thin for a diameter of 4 m because the pipe wall has already experienced a deflection in a horizontal position and pipes with a thickness of > 30 cm are known from the simulation that the pipes cannot be connected rigidly and the pipes also experience stress due to current and pipe weight. so that the stress becomes greater in the pipe.

Optimization of distribution networks for water and energy in isolated regions: A multi-objective approach incorporating ocean thermal energy conversion technologies

The limited resources and increased vulnerability to climate change and environmental degradation in isolated regions such as islands and archipelagos make the development of sustainable technologies for water and energy provision a crucial factor in addressing resource scarcity and mitigating anthropogenic impact. This work presents a multi-objective optimization analysis incorporating an Open Cycle Ocean Thermal Energy Conversion (OC-OTEC) plant in the water and energy distribution networks of an isolated region. The optimization considers three interrelated objectives: economic viability measured by annual profit, environmental sustainability reflected in reduced CO2 emissions and aquifer water usage, and social impact through job creation. The optimization results demonstrate the positive impact of integrating the OC-OTEC plant into the Tahiti distribution network, achieving an optimal configuration that balances economic, environmental, and social considerations. Finally, the proposed model is applied to Tahiti of French Polynesia as a case study.

Performance Analysis of a 10 MW Ocean Thermal Energy Conversion Plant Using Rankine Cycle in Malaysia

Ocean thermal energy conversion (OTEC) is a solution for environmental and climate change issues in the tropics. The OTEC potential in Malaysia using ocean conditions and bathymetry data has been previously studied and demonstrated. Following this, it is vital to perform a basic performance analysis of a 10 MW Rankine Cycle OTEC plant using the Malaysian ocean conditions. In this paper, the results of heat and mass balance will be reported for a 10 MW Rankine cycle OTEC plant which uses heat exchangers of plate-type and anhydrous ammonia as its working fluid. The value of a minimum objective function (γ) is derived by total heat surface area (AT) divided by the net power (PN). γ decreases when the inlet temperature difference (inlet temperature of warm seawater (TWSWI)—inlet temperature of cold seawater (TCSWI)) increases. PN is clarified to be approximately 70–80% of the PG (gross power) using Malaysian ocean conditions.

A performance study of R717 and R22 as the working fluid for OTEC plant

The purpose of this paper is to compare the thermal efficiency of an ocean thermal energy conversion (OTEC) cycle using R717 and R22 working fluids. An OTEC system typically operates at the temperature difference between the average warm surface seawater of 30 °C and the cold deep seawater of 8 °C. The temperature difference will then power a turbine to produce electricity. R22 and R717 are two potential working fluids to be used in the OTEC cycle to absorb heat due to their saturation temperature. However, R22 is associated with higher global warming potential and the global warming potential (GWP) of 1,760, compared to R717 with zero GWP. The study shows that the thermal efficiency of R22 is 0.211% higher than R717. Moreover, the thermal power required by the water circuit to cool/heat the OTEC circuit for R717 is 13% higher than R22. However, the required working fluid flow rate of the R717 system is 81.5% lower than R22, making the former significantly smaller in size.

Net Power Generation Control of OTEC Plant Using Rankine Cycle with Seawater Pumps by Warm Seawater Flow Rate Regulation*

In this research, net power generation control of an ocean thermal energy conversion (OTEC) plant using Rankine cycle is investigated. In the model construction, not only the seawater pumping powers described by static characteristics but also the net power output is taken into account. The dynamics of the heat exchangers are also considered, where they are represented as the first-order systems. For the plant model, proportional integral controller is designed so as to satisfy some specifications, where as the manipulated variable the warm seawater flow rate is adopted. The effectiveness of the proposed control system was confirmed by numerical simulations.

Free vibration and stability of a fully submerged pipe aspirating water: An experiment and new physical insights

Dynamic stability due to internal axial flow is a considerable problem for a pipe conveying fluid such as deep seawater intaking for an Ocean Thermal Energy Conversion (OTEC) plant. However, there has been much ambiguity about its dynamics, and this raises a question about whether such an aspirating pipe submerged in water flutters or not. Therefore, the objective of this paper is to provide an experiment to take a new look at the dynamics of pipe aspirating fluid (water). The experimental apparatus is constructed to eliminate expected disturbances, and we measure free damped vibrations of a submerged 4 m length pipe with internal flow. As a result, we observe the nonlinear and non-planar behavior, however, the pipe converges to the zero point and remains stable at a maximum velocity of 1.66 m/s. Subsequently, we review existing theoretical models, and present a comparison with the results from the tank experiment. In addition, we provide a new model of the inlet flow field, which plays an important role on stability, considering the flow separation and jet formed inside of the pipe entrance. This equation is solved by FEM for time integration and eigenvalue analysis, and the results seem to reproduce the experimental natural period and amplitude of the free vibration with internal flow. The model also suggests that an aspirating pipe submerged in water does not flutter up to the maximum flow velocity attainable in the experiment.

Site selection of Ocean Thermal Energy Conversion (OTEC) plants for Barbados

Tropical climates provide ideal year-round marine thermal gradients that meet the requirements for the operation of commercial Ocean Thermal Energy Conversion (OTEC) plants. This study assesses Barbados' OTEC resources and viability at several locations around the island. The island's coastline was divided into four quadrants and four proposed plant locations were selected within each quadrant based on the shortest distance to the coast. These locations were ranked via a multi-criteria decision analysis using the AHP-TOPSIS methodology. The results of the analysis ranked east coast plant locations highest, with the north, south and west coasts following in that order. The results of this study can guide OTEC development as well as marine planning and investment on the island.

Thermodynamic analysis and turbine design of a 100 kW OTEC-ORC with binary non-azeotropic working fluid

The present paper deals with the performance analysis of an ocean thermal energy conversion (OTEC) plant based on the organic Rankine cycle (ORC) with a theoretical outpower of 100 kW where a non-azeotropic mixture has been used as the working fluid. Hydrofluoroolefins (HFOs) are selected as the components of the binary non-azeotropic working fluid due to their desired thermodynamic properties, higher safety and stability, lower cost and environmental friendliness i.e., zero ODP (Ozone Depletion Potential) and low GWP (Global Warming Potential). In this study, R1224yd(Z) is adopted as the first component due to its lower flammability and toxicity comparing with other HFOs. Through comparisons between several refrigerants, R1243zf was selected as the second component of the binary non-azeotropic working fluid by considering temperature glide and the system efficiency. The performance of OTEC-ORC is also evaluated for two different working fluids i.e., R1224yd(Z)/R1243zf mixture, and pure NH3 (common working fluid in the OTEC-ORC). The optimal composition of the mixed working fluid R1224yd(Z)/R1243zf is obtained of 16:84 with the maximum system efficiency. Next, a gas turbine is designed one-dimensionally and simulated three-dimensionally. The one-dimensional calculation results fit well with the three-dimensional results. At the design point, the turbine output power is 88.63 kW and the efficiency is 87.10%. The thermodynamic findings prove that organic Rankine cycle with binary mixture of R1224yd(Z)/R1243zf is a promising alternative for pure NH3.

Suitable Site Selection for Ocean Thermal Energy Conversion (OTEC) systems – A case study for Pakistan

In developing countries such as Pakistan, the issue of generating power is crucial. As conventional power sources (fossil fuels) are depleting at an alarming rate. An abundant amount of energy is generated by thermal power plants using fossil fuels as their primary energy resource for combustion. Hence extreme uses of fossil fuels are noticed, which is greatly responsible for damaging our environment. Oceans exists around 71% of the surface area of earth and it has enormous potential for electricity generation. This study focuses on site selection for harnessing ocean energy by utilizing Ocean Thermal Energy Conversion (OTEC) systems for coastal areas of Pakistan. In this study, four sites across the coastal region of Pakistan have been studied namely Karachi, Gwadar, Ormara and Pasni. Their theoretical maximum Carnot efficiencies have also been determined and Gwadar has been identified as the most suitable location for OTEC plant with the maximum theoretical efficiency of around 6.53%, 6.93% and 7.75% at the cold-water depths of 1000m, 1200m and 1500m, respectively.

Seawater desalination through reverse osmosis driven by ocean thermal energy conversion plant: Thermodynamic and economic feasibility

Seawater desalination is an effective way to reduce water scarcity affecting many world areas. However, desalination processes require considerable power that might not be available in remote areas, especially in insular zones. Ocean Thermal Energy Conversion (OTEC) is a promising technology to be coupled with reverse osmosis (RO) in remote tropical areas thanks to the constant electricity production, the high number of equivalent hours, and the zero carbon emissions. In this study, the thermodynamic and economic feasibility of a system made of OTEC and RO for freshwater production is assessed to determine the optimal design parameters of the plant. A numerical model was created in Aspen Hysys to simulate all the main OTEC parts, including heat exchangers, pumps, turbine, and seawater pipes. For the RO unit, average performance parameters from the literature were considered. A sensitivity analysis was carried out as a function of evaporation and condensation temperatures of the cycle and riser pipe length. Furthermore, two different fluids, ammonia and R1234yf, and two different materials for the heat exchangers, stainless and polyvinylidene difluoride (PVDF), were compared. The maximum second law efficiency of 26.1% was reached with ammonia at condensation and evaporation temperatures of 13.5 °C and 23 °C, respectively, and a cold seawater depth of 800 m. Despite its higher specific cost, the adoption of stainless steel led to lower water production costs compared to PVDF because of the lower heat transfer areas required. The minimum cost of water of 2.56 $/m3 was obtained with ammonia at a cold seawater depth of 650 m for condensation and evaporation temperatures of 11 °C and 25 °C respectively.

Site Selection for Ocean Thermal Energy Conversion Plants (OTEC): A Case Study in Panama

This research addressed a need for technical evaluation of the oceanic scenario of Panama for the use of Ocean Thermal Energy Conversion (OTEC). Its bathymetry and location can potentially lead to the exploitation of OTEC, diversifying the energy matrix and helping achieve sustainability. Nevertheless, site selection for OTEC can be a complex task since it involves various alternatives, with different quantitative and qualitative criteria, which may conflict in some cases. Optimization and multiple criteria (MCD) methods have been used lately to address these issues; however, their use is still limited. Here, Analytic Hierarchical Analysis (AHP) is proposed as a MCD method for site selection. Six sites of interest were considered as the alternatives for a plant installment. These sites were chosen, excluding the environmentally and aboriginal protected areas. The quantitative criteria considered were surface and deep-water temperatures, coastline distance, gross and net efficiency. Those variables related to the efficiency, such as the water temperatures, can be considered the most influential, leading to Punta Burica, located on Panama’s Pacific coast, as the best option (96.17%).

Coupled response characteristics of cold water pipe and moored ship for floating OTEC plant

A floating Ocean Thermal Energy Conversion (OTEC) plant requires a large-diameter Cold Water Pipe (CWP) to be attached to a floating structure. For the design of the mooring system and the CWP, a coupled analysis of a floating body, mooring system and CWP should be employed due to the huge mass of the internal fluid in the CWP. The aim of this paper is to construct a simplified coupled response model to facilitate the preliminary stage of the design. The equations of equilibrium and motion are derived based on modeling as a two-dimensional floating body and an elastic pendulum. In order to verify the applicability for a practical design and limitation of the present model, a 100 MW ship-shaped platform, a spread mooring system and a CWP with an inner diameter of 12 m and a length of 800 m are configured. The results of the extreme analysis in the frequency domain with equivalent linearization of drag force by using the present model agree well with the time domain coupled analysis using OrcaFlex. Subsequently, the influence of the design parameters for CWP to the coupled responses is also clarified by a parametric study combining the bending stiffness, the linear density and the boundary conditions. The proposed model will facilitate the preliminary study with a large number of design trials, and a comprehension of the results of numerical simulations and model experiments.

An Assessment of the Financial Feasibility of an OTEC Ecopark: A Case Study at Cozumel Island

The aim of this article is to show how an OTEC Ecopark could provide comprehensive, sustainable, and quality products that satisfy the diverse needs of coastal communities in Mexico. An offshore 60 MW hybrid Ocean Thermal Energy Conversion (OTEC) plant is proposed, which will provide products that will not only fulfill the water, energy, and food needs of the coastal communities, but also energize the local blue economy. An assessment of the financial feasibility of the plant as well as a comparative analysis against other forms of energy generation was carried out. The methodology section includes a market description, literature review for the technical design, methods for mitigating socio-environmental risks, and an analysis of operational risks. To determine financial feasibility, the CAPEX, OPEX and annual revenue, including the sale of CELs and carbon credits, were evaluated. The Internal Rate of Return suggests that the system would pay for itself in year 5 of the system’s 30-year life. The methodology used for this case study, with site-specific adaptations, can be applied to other coastal communities across the globe.

Proposal of a Solar Thermal Power Plant at Low Temperature Using Solar Thermal Collectors

To this day, only two types of solar power plants have been proposed and built: high temperature thermal solar one and photovoltaic one. It is here proposed a new type of solar thermal plant using glass-top flat surface solar collectors, so working at low temperature (i.e., below 100°C). This power plant is aimed at warm countries, i.e., the ones mainly located between -40° and 40° latitude, having available space along their coast. This land based plant, to install on the seashore, is technologically similar to the one used for OTEC (Ocean Thermal Energy Conversion). This plant, apart from supplying electricity with a much better thermodynamic efficiency than OTEC plants, has the main advantage of providing desalinated water for drinking and irrigation. This plant is designed to generate electricity (and desalinated water) night and day and all year round, by means of hot water storage, with just a variation of the power delivered depending on the season.

Progress in theoretical study on constructal optimization of marine steam power plants

<p indent="0mm">Theoretical research of the constructal optimization of marine steam power plants is introduced in this study from two aspects: ship steam power plants and ocean thermal energy conversion plants. First, reviews are conducted on the main heat exchange component models of ship steam power plants, including the evaporator, superheater, economizer, whole boiler and condenser, main heat exchange, and energy conversion components, and system models of ocean thermal energy conversion plants, including the evaporator, condenser, dual-pressure turbine, and whole system. Then, constructal optimization of the main components of the two power plants and constructal thermodynamic optimization of the ocean thermal energy conversion plant based on modern thermal theories such as entropy generation minimization theory, finite time thermodynamics theory, entransy theory, and constructal theory are introduced. The similarities and differences in the results obtained before and after optimization, as well as the different optimization objectives and system structures, are extensively compared. Finally, the application prospects of constructal thermodynamic optimization to the optimal designs of energy transfer and conversion processes are made considering theoretical research on reduced energy consumption of power plants.

The Suitability of the Pacific Islands for Harnessing Ocean Thermal Energy and the Feasibility of OTEC Plants for Onshore or Offshore Processing

Ocean Thermal Energy Conversion (OTEC) relies on the thermal differences between ocean surface waters and cooler waters at c. 1000 m depth. The highest and most reliable thermal differentials are in the low latitudes, 20° either side of the equator, including the Pacific Islands region. Whilst in theory OTEC can utilize an inexhaustible amount of stored energy within the oceans, in practice the industry remains in its technical infancy, but with an increasing relevance to a post-fossil-fuel, environmentally conscious world. OTEC does not only produce electricity. OTEC-seawater utilization technologies produce high demand ocean minerals, desalination, a range of waters for aquaculture and hydroponics, and have the potential to produce large quantities of green hydrogen. OTEC is a green energy and could revolutionize the energy and economic landscape of Pacific island countries, providing reliable low-C electricity and a basis for a range of industry. This paper analyses the economics of using OTEC in combination with existing and potential future industries of importance to the Pacific (and other oceanic) regions, including tuna fisheries, seabed minerals and green hydrogen. The conclusions of these analyses suggest that OTEC has the potential to minimize carbon emissions, increase efficiencies, and create new high-quality green-technology industries and livelihoods.