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[en] The use of ocean thermal energy conversion (OTEC) to generate electricity is one of the methods proposed to utilize renewable energy and to protect the environment. In this study, simulations were performed to investigate the effect of weather conditions in the Ulsan region, Korea, on the efficiency of a solar heating OTEC (SH OTEC) system. This system utilizes solar thermal energy as the secondary heat source. Various working fluids were also simulated to select one that is suitable for this system. The results showed that R152A, R600, and R600A, in that order, were the most suitable working fluids. The effective area of the solar collector for a 20 .deg. C increase in the collector outlet temperature fluctuated from 50 to 97m'2' owing to the change in the monthly average solar gain. The annual average efficiency of the SH OTEC increases to 6.23%, compared to that of a typical conventional OTEC, which is 2-4%
[en] The earth, covered more than 70.8% by the ocean, receives most of its energy from the sun. Solar energy is transmitted through the atmosphere and efficiently collected and stored in the surface layer of the ocean, largely in the tropical zone. Some of the energy is re-emitted to the atmosphere to drive the hydrologic cycle and wind. The wind field returns some of the energy to the ocean in the form of waves and currents. The majority of the absorbed solar energy is stored in vertical thermal gradients near the surface layer of the ocean, most of which is in the tropical region. This thermal energy replenished each day by the sun in the tropical ocean represents a tremendous pollution-free energy resource for human civilization. Ocean Thermal Energy Conversion (OTEC) technology refers to a mechanical system that utilizes the natural temperature gradient that exists in the tropical ocean between the warm surface water and the deep cold water, to generate electricity and produce other economically valuable by-products. The science and engineering behind OTEC have been studied in the US since the mid-seventies, supported early by the U.S. Government and later by State and private industries. There are two general types of OTEC designs: closed-cycle plants utilize the evaporation of a working fluid, such as ammonia or propylene, to drive the turbine-generator, and open-cycle plants use steam from evaporated sea water to run the turbine. Another commonly known design, hybrid plants, is a combination of the two. OTEC requires relatively low operation and maintenance costs and no fossil fuel consumption. OTEC system possesses a formidable potential capacity for renewable energy and offers a significant elimination of greenhouse gases in producing power. In addition to electricity and drinking water, an OTEC system can produce many valuable by-products and side-utilizations, such as: hydrogen, air-conditioning, ice, aquaculture, and agriculture, etc. The potential of these by-products, especially drinking water, aquaculture and mariculture, can easily translate into billions of dollars in business opportunities. The current status of the OTEC system definitely deserves to be carefully revisited. This paper will examine recent major advancements in technology, evaluate costs and effectiveness, and assess the overall market environment of the OTEC system and describe its great renewable energy potential and overall benefits to the nations of the world
[en] Solar energy is abundant inexhaustible and nonpolluting. Its utilization does not affect the climate, and it does not lend itself to military applications. The solar-thermal, solar-electric and solar-chemical options are available. The production of low-temperature heat for warm water and for space heating, of enormous importance in the energy budget, is economic already now in many situations. Technical progress is still considerable. With the further rise in fuel prices the application will increase dramatically. Use of solar heat for large-scale generation of electricity, i.e. of power on the basis of the solar-thermal option, should be approached cautiously. Possibilities include the tower concept and ocean thermal-electric conversion (OTEC). Investment would be large, and the technology hard. Better long-term chances may be given, for decentralized application in developing countries, to the farm concept. In contrast, the chances for cheap small-scale, and later large-scale, use of solar semiconductor cells (solar-electric option) are most favourable. Technical progress is rapid, and prices drop precipitously. For the production of fuel, the solar-chemical option is in the foreground. Gaseous, liquid and convenient solid fuels can be obtained from biomass, especially by fermentation. At the moment, biogenic wastes are already available in relatively large amounts. Subsequently, energy farming is to be introduced. Biomass converted to hydrogen can be employed for production of electricity by means of fuel cells. In the more distant future, hydrogen is to be made abiotically by photolysis of water, and is to be introduced into a hydrogen economy. Probably the technology will be based on the application of synthetic membranes. It is possible that regenerative solar energy in all its forms can in the end replace all existing energy used by man. This substitution will s however, be a gradual process. (author)
[en] The energy is the basis for almost all industrial activities and domestic needs. But recently there are increasing concerns internationally over environmental problems and consequent climate changes caused by the excessive use of fossil fuels. Furthermore the price of crude oil is increasing steadily with unstable supplies. In order to solve these national energy problems, the utilization of ocean energy is introduced as one of the best alternative technologies for the future. OTEC power plant has been installed at the west Inchon power plant site. Temperature differences of 20∼25 deg. C have been utilized for plant operations, where R22 is used as a working fluid. The system is composed of low pressure turbine, plate type heat exchanger, and pumps. In the present investigation the experimental results, such as gross power, net power and objective function, are analysed when temperature differences change from the reference design point
[en] The U.S. Department of Energy (US DOE) has mobilized its National Laboratories to address the broad range of environmental effects of ocean and river energy development. The National Laboratories are using a risk-based approach to set priorities among environmental effects, and to direct research activities. Case studies will be constructed to determine the most significant environmental effects of ocean energy harvest for tidal systems in temperate estuaries, for wave energy installations in temperate coastal areas, wave installations in sub-tropical waters, and riverine energy installations in large rivers. In addition, the National Laboratories are investigating the effects of energy removal from waves, tides and river currents using numerical modeling studies. Laboratory and field research is also underway to understand the effects of electromagnetic fields (EMF), acoustic noise, toxicity from anti-biofouling coatings, effects on benthic habitats, and physical interactions with tidal and wave devices on marine and freshwater organisms and ecosystems. Outreach and interactions with stakeholders allow the National Laboratories to understand and mitigate for use conflicts and to provide useful information for marine spatial planning at the national and regional level.
[en] The marine potential in Costa Rica was evaluated in a general way, specifically in the coastal maritime areas located between the mouth of the Rio Barranca and the northern border with Nicaragua. Within the sources of marine energies were located the wave energy, tidal energy, ocean thermal energy conversion and osmotic energy. The theoretical potential of each source was estimated, through the collection of free and freely accessible information in national and international institutions. The mathematical models were used to estimate fundamental parameters in the determination of the energy potential. The actual conditions of possible sites for a utilization were observed through field visits. The field measurements were made and a photographic record was created of the sites studied. Data management was carried out in geographic information systems (GIS), through the elaboration of maps, graphs, charts, schemes and other support elements. Remote sensing models were used as support tools used. A proposed power project was a particular source, also a more detailed estimate of the potential was realized and distribution in time. Some components of the proposed project were dimensioned basic way. The proposed methodology has incorporated the concepts obtained during the investigation, and has provided a basic analysis tool to anyone who tries to take advantage of any of the sources. The favorable aspects for a possible project with marine energies were identified mainly in small scale projects without restriction. (author)
[es]El potencial marino en Costa Rica fue evaluado de manera general, especificamente en la zona maritimo costera ubicada entre la desembocadura del Rio Barranca y la frontera norte con Nicaragua. Dentro de las fuentes de energias marinas fueron ubicadas la energia undimotriz, energia mareomotriz, energia maremotermica y energia osmotica. El potencial teorico de cada fuente fue estimado, mediante la recopilacion de informacion de libre acceso y gratuita en instituciones nacionales e internacionales. Los modelos matematicos fueron utilizados para estimar parametros fundamentales en la determinacion del potencial energetico. Las condiciones reales de posibles sitios para un aprovechamiento fueron observadas mediante visitas de campo. Las mediciones de campo fueron realizadas y un registro fotografico fue creado de los sitios estudiados. El manejo de datos fue realizado en sistemas de informacion geografica (SIG), a traves de elaboracion de mapas, graficos, cuadros, esquemas y otros elementos de apoyo. Los modelos de teledeteccion fueron utilizados como apoyo a las herramientas utilizadas. Un proyecto energetico fue propuesto de una determinada fuente, tambien una estimacion mas detallada del potencial fue realizada y la distribucion en el tiempo. Algunos componentes del proyecto propuesto fueron dimensionados de manera basica. La metodologia propuesta ha incorporado los conceptos obtenidos durante la investigacion, y ha brindado una herramienta basica de analisis a quien intenta aprovechar alguna de las fuentes. Los aspectos favorables para un posible proyecto con energias marinas fueron identificados principalmente en proyectos a pequena escala sin restriccion. (autor)
[en] This paper presents the results of a case study of applying a systematic and proven process of technology portfolio planning with the use of scenario analysis to renewable energy developments in Taiwan. The planning process starts with decision values of technology development based on a survey of society leaders. It then generates, based on expert opinions and literature search, a set of major technology alternatives, which in this study include: wind energy, photovoltaic, bio-energy, solar thermal power, ocean energy, and geothermal energy. Through a committee of technical experts with diversified professional backgrounds, the process in this study next constructs three scenarios ('Season in the Sun', 'More Desire than Energy', and 'Castle in the Air') to encompass future uncertainties in the relationships between the technology alternatives and the decision values. Finally, through a second committee of professionals, the process assesses the importance and risks of these alternative technologies and develops a general strategic plan for the renewable energy technology portfolio that is responsive and robust for the future scenarios. The most important contributions of this paper are the clear description of the systematic process of technology portfolio planning and scenario analysis, the detailed demonstration of their application through a case study on the renewable energy development in Taiwan, and the valuable results and insights gained from the application.
[en] Ocean thermal energy conversion (OTEC) is a form of power generation, which exploits the temperature difference between warm surface seawater and cold deep seawater. Suitable conditions for OTEC occur in deep warm seas, especially the Caribbean, the Red Sea and parts of the Indo-Pacific Ocean. The continuous power provided by this renewable power source makes a useful contribution to a renewable energy mix because of the intermittence of the other major renewable power sources, i.e. solar or wind power. Industrial-scale OTEC power plants have simply not been built. However, recent innovations and greater political awareness of power transition to renewable energy sources have strengthened the support for such power plants and, after preliminary studies in the Reunion Island (Indian Ocean), the Martinique Island (West Indies) has been selected for the development of the first full-size OTEC power plant in the world, to be a showcase for testing and demonstration. An OTEC plant, even if the energy produced is cheap, calls for high initial capital investment. However, this technology is of interest mainly in tropical areas where funding is limited. The cost of innovations to create an operational OTEC plant has to be amortized, and this technology remains expensive. This paper will discuss the heuristic, technical and socio-economic limits and consequences of deploying an OTEC plant in Martinique to highlight respectively the impact of the OTEC plant on the environment the impact of the environment on the OTEC plant. After defining OTEC, we will describe the different constraints relating to the setting up of the first operational-scale plant worldwide. This includes the investigations performed (reporting declassified data), the political context and the local acceptance of the project. We will then provide an overview of the processes involved in the OTEC plant and discuss the feasibility of future OTEC installations. We will also list the extensive marine investigations required prior to installation and the dangers of setting up OTEC plants in inappropriate locations.
[en] In this paper a technical analysis of an ocean thermal energy conversion (OTEC) system is performed. Specifically, we present a general mathematical framework for the synthesis of OTEC power generating systems. The overall synthesis task is to minimize heat exchange area requirements, while generating some fraction of the maximum net power recoverable from hot and cold ocean water. The resulting problem formulation yields a nonlinear, nonconvex mathematical program; however, we show that globally optimal solutions for this program are easily obtained explicitly through a direct optimization approach with minimal computational effort over a wide range of thermodynamic conditions. The proposed analysis is demonstrated on a case study involving the generation of hydrogen by an OTEC system with a pure ammonia working fluid