Closed-cycle Ocean Thermal Energy Conversion Research Articles

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.

Thermodynamic Analysis of a Closed-Cycle Ocean Thermal Energy Conversion Power Plant for Offshore Platforms

Abstract The world is currently facing two major challenges: global climate change and sustainable development. Efforts to generate electricity from renewable energy sources continue steadily. In this study, a closed-cycle ocean thermal energy conversion (OTEC) power plant with various working fluids with zero Ozone Depletion Potential (ODP) and per unit mass flow rate for offshore platforms is designed and thermodynamically analyzed using Engineering Equation Solver (EES). The calculated results shows that ammonia (R-717) has the highest electrical performance of 45.51 kW per unit mass flow rate among the studied working fluids for OTEC. Introduction The world is currently confronted with two major challenges: global climate change and sustainable development. The Paris Agreement entered into force on November 4, 2016, limited global warming to well below 2°C, preferably to 1.5°C, compared to preindustrial levels. According to the Sixth Assessment Report released by Intergovernmental Panel on Climate Change (IPCC) on February 28, 2022, climate change is causing common deterioration in every zone in the world with just 1.1°C of warming. Sustainable solutions for our environment’s future must be produced. Therefore, the power generation efforts from renewable energy sources are going on continuously.

소형 LNG 재기화 시스템의 기화열을 열침으로 하는 해수온도차발전 사이클 성능분석

Demand for LNG, mainly in Asia, continues to increase in order to achieve the reduction of greenhouse gas emission and decarbonization goals. For the convenience of transport, natural gas is stored in a liquefied state and needs to be vaporized for reuse. A huge amount of cold heat is generated through the process of LNG re-gasification. In this study, the performance analysis of the closed cycle ocean thermal energy conversion (CC-OTEC) system using the vaporization cold heat of a small LNG regasification system as heat sink and warm surface seawater as a heat source was performed. After configuring the CC-OTEC with the working fluid as R32 in the LNG regasification system at 10 kg per second, the turbine inlet pressure changed from 15 bar to 17 bar. Gross power, net power, efficiency and parasitic load were analyzed. At the turbine inlet presusure of 16.2 bar, we exhibited the maximum net power of 198.5 kW and the maximum efficiency 2.78%.

Optimal offering strategy of virtual power plant with hybrid renewable ocean energy portfolio

This paper proposes a hybrid ocean energy system to form a virtual power plant (VPP) for participating in electricity markets in order to promote the renewable ocean energy utilization and accommodation. In the proposed system, solar thermal energy is integrated with the closed-cycle ocean thermal energy conversion (OTEC) to boost the temperature difference between surface and deep seawater for efficiency and flexibility improvements, and the thermodynamic effects of seawater mass flow rates on the output of solar-boosted OTEC (SOTEC) are exploited for deploying SOTEC as a renewable dispatchable unit. An optimal tidal-storage operation model is also developed to make use of the subsea pumped storage (SPS) with hydrostatic pressures at ocean depth for mitigating the intermittent tidal range energy in order to make the arbitrage in the electricity market. Furthermore, a two-stage coordinated scheduling strategy is presented to optimally control seawater mass flow rates of SOTEC and hydraulic reversible pump-turbines of SPS for enhancing the daily VPP profit. Comparative studies have been investigated to confirm the superiority of the developed methodology in various renewable ocean energy and electricity market price scenarios.

Simulation Data of Regional Economic Analysis of OTEC for Applicable Area

To mitigate the power shortage problem in the South Pacific island nations and the equatorial area, we studied the development characteristics of ocean thermal energy conversion (OTEC) using abundant clean ocean energy. Through the simulation of open- and closed-cycle OTEC, the generation amount and its economic efficiency were compared, and the application characteristics of the power generation cycle according to the seawater temperature distribution were compared by applying various seawater temperature conditions. According to the characteristics of seawater heat sources in the region, the power generation output was about 883.2 kW in Samoa, and the average power generation by region was about 650.5 kW for the open-cycle OTEC model. Regional revenue up to approximately $8,487,000 was generated in Kiribati, driven by the higher electricity tariff of $0.327/kWh and high water costs of $5.86/ton. With the spread of 50 MW commercial plants, Kiribati had a high net present value of $1,930,402,000, and its internal rate of return was more than 37.0%. This paper is presents a method of securing economic feasibility of OTEC according to various heat source conditions and economic conditions in the region, while it also analyzes the capacity and type of the power plant.

Site Determination for OTEC Turbine Installation of 100 MW Capacity in North Bali Waters

This research was conducted to investigate a suitable location for the OTEC (Ocean Thermal Energy Conversion) pilot plant in North Bali. The investigation was done by calculating the theoretical potential of electric power output using the method of Uehara and Ikegami (1990) for closed cycle OTEC. OTEC power plants require a temperature difference between surface and bottom water layers at least 20°C. Temperature data were obtained from the HYCOM temperature model for a period of 9 years (2008 - 2017) at 4 points which were verified with field data taken in 2017 using KR Geomarin III. The results of field measurements show that the sea surface temperature (SST) in the study area ranges from 28 to 31°C while at depth of 800 m 5.75°C. ∆T values range from 22 to 25°C. Verification of modelling temperature and measurement temperature shows that the modeling results resemble the temperature of North Bali Waters. Analyses results for the four points showed that B-11, located in the Tedjakula area, has the largest electrical power output (71,109 MW). Thus, point B-11 is the best location for development of OTEC pilot plant in North Bali Waters.

Analysis of Ocean Thermal Energy Conversion Power Plant using Isobutane as the Working Fluid

The use of organic isobutane will be investigated for a closed-cycle Ocean Thermal Energy Conversion (OTEC) onshore plant that delivers 110 MW electric powers. This paper will cover concept, process, energy calculations, cost factoids and environmental aspects. In isobutane cycle, hot ocean surface water is used to vaporize and to superheat isobutane in a heat exchanger. Isobutane vapor then expands through a turbine to generate useful power. The exhaust vapor is condensed afterwards, using the cold deeper ocean water, and pumped to a heat exchanger to complete a cycle. Results show the major design characteristics and equipment's of the OTEC plant along with cycle efficiency and cycle improvement techniques.

Thermo-economic analysis of an ocean thermal power plant for a Nigerian coastal region

ABSTRACTThis paper presents a thermo-economic analysis of an ocean thermal energy conversion (OTEC) power plant for a Nigerian coastal region at latitude 4°00′–4°16′N, and longitude 7°16′–7°19′E, whose energy potential is at 22 and 24 K across 1 km from the sea water surface during rainy and dry seasons, respectively. An ammonia closed cycle OTEC plant was designed to constantly supply 100 MW of electricity all year round to the region. The results of the analysis compared favourably with those for similar plants. The plant’s unit cost of energy was found to be 0.11US$/kWh when compared to 0.1US$/kWh for the municipal energy supply. The break-even point was also found to be 12 years. However, as a result of the high initial installed capital cost of 7954.37US$/kW and life cycle cost of 1.30bUS$, only very large organisations would be able to venture into this project.

Design and performance analysis of radial-inflow turboexpander for OTEC application

Ocean thermal energy conversion (OTEC) is a potential source of renewable energy. In order to design a turbine for maximizing the output power for very low working temperature application like OTEC, careful one-dimensional design followed by detailed three dimensional simulation is required. In this work a radial-inflow turbine with R-22 as working fluid is designed for a closed-cycle ocean thermal energy conversion plant of 2 kWe capacity. Design speed of the turbine is 34000 rpm. Inlet and outlet temperatures of designed turbine are 24.5 °C and 14 °C respectively. Three-dimensional fluid flow analysis inside the turbine at design and off-design conditions were carried out. Important dimensions of the turbine are: rotor tip and shroud radii of 24 mm and 19 mm respectively; blade widths at rotor inlet and outlet of 6 mm and 11 mm respectively; axial length of 17.5 mm; diffuser of 62 mm long. Volute casing designed has a circular cross section. The importance of the number of blades, blade filleting and stagger angle from the point of view of turbine performance are reported.

Off-design performance analysis of a closed-cycle ocean thermal energy conversion system with solar thermal preheating and superheating

This article reports the off-design performance analysis of a closed-cycle ocean thermal energy conversion (OTEC) system when a solar thermal collector is integrated as an add-on preheater or superheater. Design-point analysis of a simple OTEC system was numerically conducted to generate a gross power of 100 kW, representing a base OTEC system. In order to improve the power output of the OTEC system, two ways of utilizing solar energy are considered in this study: (1) preheating of surface seawater to increase its input temperature to the cycle and (2) direct superheating of the working fluid before it enters a turbine. Obtained results reveal that both preheating and superheating cases increase the net power generation by 20–25% from the design-point. However, the preheating case demands immense heat load on the solar collector due to the huge thermal mass of the seawater, being less efficient thermodynamically. The superheating case increases the thermal efficiency of the system from 1.9% to around 3%, about a 60% improvement, suggesting that this should be a better approach in improving the OTEC system. This research provides thermodynamic insight on the potential advantages and challenges of adding a solar thermal collection component to OTEC power plants.

Performance Analysis of 15 kW Closed Cycle Ocean Thermal Energy Conversion System With Different Working Fluids

Closed cycle ocean thermal energy conversion (CC-OTEC) is a way to generate electricity by the sea water temperature difference from the upper surface to the different depth. This paper presents the performance of a 15 kW micropower CC-OTEC system under different working fluids. The results show that both butane and isobutane are not proper working fluids for the CC-OTEC system because the inlet stable operating turbine pressure is in a very narrow range. R125, R143a, and R32, especially R125, are suggested to be the transitional working fluids for CC-OTEC system for their better comprehensive system performance. Moreover, it is recommended that propane should be a candidate for the working fluid because of its excellent comprehensive properties and environmental friendliness. However, propane has inflammable and explosive characteristics. As for the natural working fluid ammonia, almost all performance properties are not satisfactory except the higher net output per unit sea water mass flow rate. But ammonia has relative broader range of the stable operating turbine inlet pressure, which has benefits for the practical plant operation.

Study and Enhancement of Flash Evaporation Desalination Utilizing the Ocean Thermocline and Discharged heat

� Abstract—This paper reports on the results of experimental investigations of flash evaporation from superheated jet issues vertically upward from a round straight nozzle of 81.3 mm diameter. For the investigated range of jet superheat degree and velocity, it was shown that flash evaporation enhances with initial temperature increase. Due to the increase of jet inertia and subsequently the of jet shattering, increase of jet velocity was found to result in increase of evaporation delay period. An empirical equation predicts the jet evaporation completion height was developed, this equation is thought to be useful in designing the flash evaporation chamber. In attempts for enhancement of flash evaporation, use of steel wire mesh located at short distance downstream was found effective with no consequent pressure drop. Keywords—Enhancement; Flash Evaporation; OTEC; superheated jet I. INTRODUCTION S a result of the shortage of energy resources and the environmental pollution accompanying the combustion of fossil fuels to generate electricity and it's major contribution to the global warming problem, along with the scarcity of fresh water resource; energy and water issues are obtaining a considerable interest of researchers and concerning authorities likewise. Conversion of renewable energy resources is promoting and can solve the energy and environmental problems, while desalination of saline water bodies which form the majority of water resources on the earth can definitely substitute the shortage of fresh water. Ocean Thermal Energy conversion (OTEC) is one of the promising technologies to utilize the temperature difference between the hot shallow water and cold deep water of ocean to drive a certain power cycle and generate electricity, this process requires a huge quantity of both hot and cold water to be pumped from the ocean to supply the OTEC power plant; for the ultimate usage of this pumped water, desalination plant should be combined with the closed-cycle OTEC plant, where the discharged water from the electricity generation plant supply the flash evaporation based desalination plant. As the

Optimization of a Closed-Cycle OTEC System

Optimization of an Ocean Thermal Energy Conversion (OTEC) system is carried out by the Powell Method (the method of steepest descent). The parameters in the objective function consist of the velocities of cold sea water and warm sea water passing through the heat exchangers, the phase change temperature, and turbine configuration (specific speed, specific diameter, ratio of blade to diameter). Numerical results are shown for a 100-MW OTEC plant with plate-type heat exchangers using ammonia as working fluid, and are compared with calculation results for the case when the turbine efficiency is fixed.

Potential environmental impacts of closed-cycle ocean thermal energy conversion

Closed-cyle OTEC can be design to be a relatively benign technology when compared with conventional energy production methods. However, a number of potentially significant environmental concerns have been identified above. These include impacts of: • • atmospheric or marine working fluid, biocide or trace constitutent releases; • • air and water quality degradation during construction, deployment, and site preparation; • • artificial upwelling; • • destruction of terrestrial habitats; • • discharges on land or into wells; • • biota attraction; • • impingement and entrainment (primary or secondary); • • redistribution of oceanic constituents; • • alteration of coastal wave conditions, sediment transport, or currents; • • social, economic, or aesthetic changes; • • ciguatera outbreaks; and • • credible accidents. It is essential that all potentially significant concerns be examined and assessed for each site and design to assure that OTEC is an environmentally benign and safe alternative to conventional power generation.

Ocean thermal energy conversion: technology development

The United States is developing four ocean-energy technologies which offer significant promise. These are: ocean thermal energy conversion (OTEC), wave power, ocean currents, and salinity gradients. The major funding emphasis has been in OTEC because of its potential, state of development, and availability of the resource to U.S. shores. The closed-cycle OTEC concept, with ammonia as the working fluid, has been emphasized in the U.S. Department of Energy Program, based on analyses which concluded that the closed cycle has the highest probability of achieving early economic viability. Closed-cycle systems have been used in two OTEC conceptual design configurations for 10 to 40 megawatt (MW) pilot plants; viz., a moored plant to produce electrical power for transmission ashore via cable; and a grazing plant to produce energy intensive products on-board such as ammonia. The OTEC technology development program has experimentally verified much of the analytical work and many of the component preliminary designs for the OTEC 10 40 MW pilot plant. This paper summarizes the technological accomplishments, major findings, remaining problems and action planned. The areas of major concern pertain to the cost-effective designs for the heat exchangers, including biofouling countermeasures, cold water pipe, and electrical umbilical cable and the successful system integration of these components into a working plant that can be readily deployed and operated at sea over a design life of 30 years. The 1 MW system, OTEC-1, will be constructed and ready for deployment for at-sea test in mid 1980. The preliminary designs for the 10 40 MW pilot plant is expected to be initiated in fiscal year 1981, with subsequent construction and deployment planned for the end of fiscal year 1985. Many technological advances have been made toward achieving the program objectives for proving the technical and economic feasibility and minimizing engineering risks for eventual commercial applications.

Generalized Parameters for Selection of Turbines and Working Fluids for OTEC Power Systems

The choice of working fluid has a significant impact on the size and design characteristics of turbines for closed cycle OTEC (Ocean Thermal Energy Conversion) power systems. This paper examines turbine sizes and speeds for various candidate working fluids. The turbine performance and design limits are strongly influenced by blade stress criteria which have been ignored by previous investigators. Illustrative design parameters are given for a turbine using ammonia and scaling parameters are listed to compare the power outputs of turbines using other fluids. The design of a turbine for open-cycle OTEC power systems is largely dictated by the very high specific volume of the exhaust steam at a pressure of about 0.14 psia. In order to minimize the cost of turbines and generators through economy of scale, it is desirable to maximize the power output of a single turbine, and this leads to very large diameters and blade lengths. This paper explores the considerations which influence the choice of turbine size, blade length, speed, power output and efficiency.