Search Results (47)

Small Island Developing States (SIDS) face energy security challenges due to reliance on imported fossil fuels and limited land for renewable energy. This study evaluates the techno-economic feasibility of integrating Ocean Thermal Energy Conversion (OTEC) and Seawater Air Conditioning (SWAC) systems as a sustainable solution. The research focuses on (1) developing a scalable onshore OTEC-SWAC system and assessing feasibility across 32 SIDS using 20 years of oceanic and atmospheric data, (2) analyzing key system parameters such as pipeline length, pump sizing, and cooling requirements and their effect on capital cost, and (3) developing a scalable cost estimation model for Levelized Cost of Energy (LCOE) predictions. The techno-economic analysis reveals that 30 of the 32 SIDS are technically feasible for OTEC power generation with a temperature gradient of 20 °C. The proposed system is economically feasible in 23 of the SIDS with a calculated average LCOE of 0.16 USD/kWh, which is 67% lower than the diesel LCOE, which is on average 0.46 USD/kWh, making it a cost-competitive alternative. The developed reduced form of the model enables scalable LCOE calculations based on pipeline length and ocean temperature differentials, aiding policymakers in decision-making. By reducing fossil fuel dependency and supporting green tourism, this study provides actionable insights for sustainable energy adoption in SIDS. Full article

Ocean thermal energy is an emerging energy source that holds great promise, especially for tropical countries. Ocean thermal energy conversion (OTEC) efficiency can be improved by raising the temperature difference between the hot water and the cold water. In the work reported here, a laboratory-scale closed-cycle OTEC system was constructed and tested for power output and efficiency. A solar heating system heated the water up to 70 °C. Experiments were conducted at cold water inlet temperatures of 5 °C, 8 °C, and 11 °C. The mass flow rate of the hot water was varied, while that of the cold water was kept constant. Increasing the hot water inlet temperature from 30 °C to 70 °C while keeping the cold water inlet temperature constant at 5 °C at the highest mass flow rate of hot water increased the power output from 32.07 W to 66.68 W (107.9% increase) and the thermal efficiency from 1.96% to 4.37% (123% increase). The pressure drop across the turbine was higher for a larger temperature difference between the hot water and cold water, indicating a higher transfer of energy to the working fluid. Increasing the mass flow rate of the hot water for the increasing temperature difference between the hot water and cold water increased the power output and efficiency due to the increase in the energy transfer from the hot water to the working fluid. Experimental works on solar-boosted OTEC systems are very rare, and this work should pave the way for practical implementation. Full article

In order to achieve the goals of carbon neutrality and reduced carbon emissions, China is increasingly focusing on the development and utilization of renewable energy sources. Among these, ocean thermal energy conversion (OTEC) has the advantages of small periodic fluctuations and large potential reserves, making it an important research field. With the development of the “Maritime Silk Road”, the Xisha Islands in the South China Sea will see a growing demand for electricity, providing the potential for OTEC development in this region. Optimal site selection of OTEC power plants is a prerequisite for developing thermal energy provision, affecting both the construction costs and future benefits of the power plants. This study establishes a scientific evaluation model based on the decision-making frameworks of geographic information systems (GISs) and multi-criteria decision-making (MCDM) methods, specifically the analytic hierarchy process (AHP) for assigning weights, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) to reclassify the factors, and weighted linear combination (WLC) to compute the suitability index. In addition to commonly considered factors such as temperature difference and marine usage status, this study innovatively incorporates geological conditions and maximum offshore distances of cold seawater based on cost control. The final evaluation identifies three suitable areas for OTEC development near the Xuande Atoll and the Yongle Atoll in the Xisha Sea Area, providing valuable insights for energy developers and policymakers. Full article

With the progress of research on ocean thermal energy conversion, the stabI have checked and revised all. le operation of ocean thermal energy conversion experiments has become a problem that cannot be ignored. The control foundation for stable operation is the accurate prediction of operational performance. In order to achieve accurate prediction and optimization of the performance of the ocean thermal energy conversion experimental platform, this article analyzes the experimental parameters of the turbine based on the basic experimental data obtained from the 50 kW OTEC experimental platform. Through the selection and training of experimental data, a GA-BP-OTE (GBO) model that can automatically select the number of hidden layer nodes was established using seven input parameters. Bayesian optimization was used to complete the optimization of hyperparameters, greatly reducing the training time of the surrogate model. Analyzing the prediction results of the GBO model, it is concluded that the GBO model has better prediction accuracy and has a very low prediction error in the prediction of small temperature changes in ocean thermal energy, proving the progressiveness of the model proposed in this article. The dual-objective optimization problem of turbine grid-connected power and isentropic efficiency is solved. The results show that the change in isentropic efficiency of the permeable device is affected by the combined influence of the seven parameters selected in this study, with the mass flow rate of the working fluid having the greatest impact. The MAPE of the GBO model turbine grid-connected power is 0.24547%, the MAPE of the turbine isentropic efficiency is 0.04%, and the MAPE of the turbine speed is 0.33%. The Pareto-optimal solution for the turbine grid-connected power is 40.1792 kW, with an isentropic efficiency of 0.837439. Full article

A large amount of thermal energy is stored in the oceans between the tropics, available for conversion into electrical energy using OTEC technology. The aim of this study was to determine the annual and seasonal variability of the oceanic thermal resource in Mexico. Using the WOA18 database, we mapped surface temperature at a 10 m depth, deep cold water (<5 °C), vertical temperature difference (18 and 20 °C), and temperature anomalies. From the results, four areas were analyzed as being suitable for the installation of OTEC technology: Pacific (A), Los Cabos (B), Caribbean (C), and Gulf of Mexico (G). The optimal thermal resource (≥20 °C) was found between a 400 and 1000 m depth in all seasons in A and C, in spring, summer, and autumn in G, and only in summer and autumn in B. The suboptimal thermal resource (between 18 and 20 °C) was present between 400 and 800 m in all seasons in A, C, and G, and in summer and autumn in B. These results provide new information of utmost importance for future location and design considerations of OTEC plants on Mexican coasts, and the methodology can be used in other areas where there is a lack of field data and the development of OTEC technology is being considered. Full article

A lack of natural resources drives the oil dependency in Pacific Island Countries and Territories (PICTs), hampering energy security and imposing high electricity tariffs in the region. Nevertheless, the Western Equatorial Pacific is known for its large Sea Surface Temperature (SST) and deep-sea water (DSW) temperature difference favorable for harvesting thermal energy. In this study, we selected 18 PICTs in the western Equatorial Pacific to estimate Annual Energy Production (AEP) for a 1 MW class Ocean Thermal Energy Conversion (OTEC) plant. We combined the DSW temperature from the mean in situ Argo profiles and 1 km resolution satellite SST data to estimate the thermal energy resource resolving the fine features of the island coastline. Furthermore, the twenty-year-long SST dataset was used to analyze the SST variability. The analysis showed that Equatorial islands and Southern islands have the highest inter-annual variability due to El Nino Southern Oscillation (ENSO). The power density varied from 0.26 to 0.32 W/m² among the islands, with the lowest values found for the southernmost islands near the South Equatorial Countercurrent. Islands within the South Equatorial Current, Equatorial Undercurrent, and North Equatorial Countercurrent showed the highest values for both power density and gross power. Considering a 1 MW class OTEC plant, Annual Energy Production (AEP) in 2022 varied from 7 GWh to 8 GWh, with relatively low variability among islands near the Equator and in low latitudes. Considering the three variables, AEP, SST variability, and distance from the shore, Nauru is a potential candidate for OTEC, with a net power of 1.14 MW within 1 km from the shore. Full article

In recent years, clean and renewable energy sources have received much attention to balance the contradiction between resource needs and environmental sustainability. Among them, ocean thermal energy conversion (OTEC), which consists of surface warm seawater and deep cold seawater, can rely on thermal cycling to generate electricity and has great potential in alleviating the energy crisis. In this paper, the design and experiment study of a 50 kW OTEC platform is proposed. Thermodynamic modeling, calculation, optimization, and engineering calibration of the system were carried out, and the thermal efficiency reached 2.63% to meet the power generation demand. Experiments were also carried out by using a heat pump unit to simulate hot and cold seawater environments, and data on the stable operation of the system were obtained, with the grid-connected power reaching 47.5 kW and a thermal efficiency of 2.46%. The accuracy of the design scheme is verified, and the theoretical basis and data support are provided for the practical development and application of ocean thermal energy conversion. Full article

This research focuses on enhancing the efficiency of Bi₂Te₃-based thermoelectric generators (TEGs) in ocean thermal energy conversion (OTEC) systems through innovative heat exchanger designs. Our comparative study uses computer simulations to evaluate three types of heat exchangers: cavity, plate-fins, and longitudinal vortex generators (LVGs). We analyze their impact on thermoelectric conversion performance, considering the thermal energy transfer from warm surface seawater to TEGs. The results demonstrate that heat exchangers with plate-fins and LVGs significantly outperform the cavity heat exchanger regarding thermal energy transfer efficiency. Specifically, plate-fins increase TEG output power by approximately 22.92% and enhance thermoelectric conversion efficiency by 38.20%. Similarly, LVGs lead to a 13.02% increase in output power and a 16.83% improvement in conversion efficiency. These advancements are contingent upon specific conditions such as seawater flow rates, fin heights, LVG tilt angles, and locations. The study underscores the importance of optimizing heat exchanger designs in OTEC systems, balancing enhanced heat transfer against the required pump power. Our findings contribute to a broader understanding of materials science in sustainable energy technologies. Full article

The effective utilization of renewable energy has become critical to technological advancement for the energetic transition from fossil fuels to clean and sustainable sources. Ocean Thermal Energy Conversion (OTEC) technology, which generates electricity by leveraging the temperature differential between surface and deep ocean waters, enables stable power generation around the clock. In this domain, the combination of thermoelectric generators (TEGs) and heat exchangers has exhibited immense potential for ameliorating the deficiencies of conventional OTEC. This study uses finite element numerical simulation of the COMSOL5.5 software to investigate the fluid dynamics characteristics of heat exchangers with flat fins and different types of longitudinal vortex generators (LVGs) under the same number of fins. This research encompasses heat exchangers with rectangular, triangular, and trapezoidal LVGs. Concurrently, the analysis examines how the vortices generated by the LVGs influence the thermoelectric performance of the TEGs. The results demonstrate that heat exchangers integrating flat fins and LVGs can enhance the power generation efficiency of TEGs. However, the pumping power required by the LVGs constrains the thermoelectric conversion efficiency. Compared to rectangular and triangular LVGs, trapezoidal LVGs achieve a superior balance between output and pumping power. Heat exchangers utilizing trapezoidal LVGs can attain the highest TEG thermoelectric conversion efficiency with a specific seawater flow velocity. Overall, these findings provide valuable reference information for applying TEGs and heat exchangers in OTEC design. Full article

In this paper, a 100 kW radial inflow turbine is designed for an ocean thermal energy conversion (OTEC) power plant based on the organic Rankine cycle (ORC) with ammonia as the working fluid. Based on one-dimensional (1D) and three-dimensional computational fluid dynamics (3D-CFD) modeling, the mechanical structure design, static and modal analyses of the turbine and its components are carried out to investigate its mechanical performance. The results show the stress and strain distribution in the volute, stator and rotor, and their maximum values appear, respectively, at the inlet cutout, the tip of the stator outlet and the connection position between the rotor and the shaft. After optimization, all the stresses in the above components are below the allowable values. The frequencies from the first order to the sixth order of the rotor and whole turbine were obtained through modal analysis without prestress and under prestress. The maximum frequency of the rotor and whole turbine is 707.75 Hz and 40.22 Hz, both of which are far away from the resonance frequency range that can avoid resonance. Therefore, the structure of the designed turbine is safe, feasible and reliable so as to better guide actual production. Full article

The transportation of seawater on a grand scale via an ultra-large cold-water pipe situated within the context of ocean thermal energy conversion (OTEC) floating installations inherently presents challenges associated with instability and potential malfunction in the face of demanding operational circumstances. This study endeavors to augment the stability and security of cold-water pipe (CWP) operations by scrutinizing their vibrational attributes across diverse boundary configurations. Initially, we invoke Euler–Bernoulli beam theory to forge the analytical framework and proffer a semi-analytical resolution by utilizing the generalized integral transform technique (GITT). Subsequently, we authenticate the convergence and precision of our proposed approach through comparative analysis with extant theories. Our findings underscore the conspicuous influence of boundary conditions on the convergence of transverse displacement. The influence of internal flow on the transverse displacement and the natural frequency manifests substantial variability under different boundary conditions. Significantly, an escalation in the internal flow velocity triggers a concomitant reduction in the natural frequency, ultimately culminating in instability once the critical velocity threshold is reached. Additionally, the reliance of the transverse displacement and the natural frequency on the clump weight at the bottom is markedly pronounced. Our discoveries propose that pipe stability can be ameliorated by adjusting the clump weight at the bottom. Furthermore, the novel insights obtained through our proposed approach can significantly aid in the early-stage design and analysis of CWP. Full article

Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by utilizing the temperature difference between deep cold water and surface warm water. The cold-water pipe (CWP) is a key component of OTEC systems, which transports deep cold water to the floating platform. The CWP is subjected to various environmental and operational loads, such as waves, currents, internal flow, and platform motion, which can affect its dynamic response and stability. In this paper, we establish a computational model of the mechanical performance of the CWP based on the Euler–Bernoulli beam theory and the Morrison equation, considering the effects of internal flow, sea current, and wave excitation. We use the differential quadrature method (DQM) to obtain a semi-analytical solution of the lateral displacement and bending moment of the CWP. We verify the correctness and validity of our model by comparing it with the finite element simulation results using OrcaFlex software. We also analyze the effects of operating conditions—such as wave intensity, clump weight at the bottom, and internal flow velocity—on the dynamic response of the CWP using numerical simulation and the orthogonal experimental method. The results show that changing the wave strength and internal flow velocity has little effect on the lateral displacement of the CWP but increasing the current velocity can significantly increase the lateral displacement of the CWP, which can lead to instability. The effects of waves, clump weight, internal flow, and sea current on the maximum bending moment of the CWP are similar; all of them increase sharply at first and then decrease gradually until they level off. The differences in the effects are mainly reflected in the different locations of the pipe sections. This paper suggests some design guidance for CWP in terms of dynamic responses depending on the operating conditions. This paper contributes to the journal’s scope by providing a novel and efficient method for analyzing the mechanical performance of CWP for OTEC systems, which is an important ocean energy resource. Full article

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 (A_T) divided by the net power (P_N). γ decreases when the inlet temperature difference (inlet temperature of warm seawater (T_WSWI)—inlet temperature of cold seawater (T_CSWI)) increases. P_N is clarified to be approximately 70–80% of the P_G (gross power) using Malaysian ocean conditions. Full article

South Korea is currently in the preparatory stage of commercializing an ocean thermal energy conversion (OTEC) system, as the demonstration of a 1 MW scale OTEC system has been accomplished. However, the commercialization of OTEC requires the establishment of a control system for various environmental changes. Therefore, pre-emptive identification of the system’s risk factors and the process of analyzing the impact of the system, building control items, and optimizing control are necessary. This study aims to establish and analyze an optimized control system for MW-scale OTEC risk factors, such as the shutdown of seawater or refrigerant pumps. The selected OTEC system was designed for 1070 kW class facilities, with a 36.6% portion of total electricity usage by the seawater pump and refrigerant pump. As a result, an on/off control system was adopted in order to eliminate the risk factors. By adjusting this option, dry operation of the refrigerant pump, water hammering, and liquid inflow into the turbine were successfully prevented. To be more specific, the initial system was to be shut down due to a sharp decrease in power at the point where the deep seawater flow rate was 538 kg/s (35.7% of max flow rate) and the surface seawater flow rate was 715 kg/s (38.4% of max flow rate). This situation was improved by adopting parallel operation of seawater pumps and on/off control, thereby leading to a more stabilized operation by maintaining a flow rate of over 1864 kg/s for surface seawater and 1507 kg/s for deep seawater. Moreover, it was confirmed that the flow rate of the pump was reduced by 1.89 kg/s per second in the process of pump shutdown during a single operation mode of the refrigerant pump. Parallel operation made it possible to maintain 60.2% of the output by increasing the power of the second pump’s flow rate in the event of the first pump shutting down. The final seawater temperature differential power generation model derived from this study consists of two refrigerant pumps and two surface seawater and deep seawater pumps in order to prevent system shutdown caused by a single pump failure. The final design was reflected in the final delivery to Kiribati, which is located near the equator. Full article