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[en] In Central Receiver Systems (CRSs), thousands of heliostats track the sunrays and reflect beam radiation on to a receiver surface. The size of the reflected image and the extent of reflection from the heliostats are one of the important criteria that need to be taken into account while designing a receiver, since spillage losses may vary from 2 to 16% of the total losses. The present study aims to determine the size of an external cylindrical receiver, such that the rays reflected from all the heliostats in the field are intercepted. A dimensionless correlation with respect to tower height and receiver size (diameter and height) as a function of heliostat size and its position is discussed in the paper. This correlation could be used as a first-order approximation to estimate the receiver dimensions. When applied to the Ivanpah Solar Electricity Generating Station (ISEGS) plant, the correlation yields satisfactory estimation of receiver dimensions.
[en] The temperature fields of seven layer thin disks of the receiving elements with inner and outer heating system with the temperature of upper surface: 1) of the first layer; 2) of the six layer, which equal to the temperature of the environment are obtained. The analysis of coefficients of receiving element heating non-equivalence is given. (author)
[en] In the following study a complete balance over the REFOS receiver module, mounted on the tower power plant CESA-1 at the Plataforma Solar de Almeria (PSA), is carried out. Additionally an error inspection of the various measurement techniques used in the REFOS project is made. Especially the flux measurement system Pro hermes that is used to determine the total entry power of the receiver module and known as a major error source is analysed in detail. Simulations and experiments on the particular instruments are used to determine and quantify possible error sources. After discovering the origin of the errors they are reduced and included in the error calculation. The ultimate result is presented as an overall efficiency of the receiver module in dependence on the flux density at the receiver modules entry plane and the receiver operating temperature. (Author) 26 refs
[en] Highlights: • Monthly energy and exergy analyses of the solar driven sCO_2 Brayton system were conducted. • The analyses were conducted for three power outputs. • Monthly variations of heat fractions from the system components during day and night time were evaluated. • Monthly assessment of the solar multiple for day and night time is presented. • Detailed exergy analysis was conducted for both the solar system and sCO_2 Brayton system. - Abstract: A performance assessment of sizing an auxiliary boiler for a solar driven supercritical double recompression CO_2 Brayton cycle was conducted. The Brayton cycle is designed to deliver three different power outputs and the required size of the auxiliary boiler was examined in detail. The heat fraction to be delivered from the solar field and from the auxiliary boiler for each month of the year are reported. Furthermore, the daytime solar multiple and the twenty-four hour solar multiple were examined. Another key parameter that was studied is the effect of the turbine inlet temperature on the net power, energy efficiency, and exergy efficiency. Among the other exergy parameters that were examined are exergy destruction, exergy improvement potential, fuel depletion ratio, relative irreversibility, and productivity lack. The power output for Case 1, Case 2, and Case 3 is about 41.5 MW, 60.0 MW, and 90.0 MW, respectively; and for the month of June, the fraction of the heat from the auxiliary boiler during daytime hours is about 0.25, 0.40, and 0.54, respectively. For the three Cases the overall system energy efficiency during the month of June is 20.7%, 25.0%, 29.6%, and the overall system exergy efficiency is 22.2%, 28.3%, and 35.7%, respectively. The cycle efficiency is about 47% for the baseline conditions. In addition, the lowest thermal heat collected in the receiver is during December and, therefore, during this month, the highest auxiliary heat is required from the boiler. The 24-h average solar multiple for Case 1, Case 2, and Case 3 is 0.437, 0.303, and 0.202, respectively; and the average daytime solar multiple for these cases is 0.858, 0.590, and 0.396, respectively. Moreover, similar results are reported for each month of the year. Furthermore, the findings demonstrate that the heliostat has the highest exergy destruction rate and, thus, it has the highest exergy improvement potential.
[en] This report describes a project by Science Applications International Corporation and its subcontractors Boeing/Rocketdyne and Bechtel Corp. to develop manufacturing technology for production of SAIC stretched membrane heliostats. The project consists of three phases, of which two are complete. This first phase had as its goals to identify and complete a detailed evaluation of manufacturing technology, process changes, and design enhancements to be pursued for near-term heliostat markets. In the second phase, the design of the SAIC stretched membrane heliostat was refined, manufacturing tooling for mirror facet and structural component fabrication was implemented, and four proof-of-concept/test heliostats were produced and installed in three locations. The proposed plan for Phase III calls for improvements in production tooling to enhance product quality and prepare increased production capacity. This project is part of the U.S. Department of Energy's Solar Manufacturing Technology Program (SolMaT)
[en] Solar energy has received much interest in recent years, being a clean (free of pollution or other environmental damage) and inexhaustible energy source. It is also considered safer than some other non conventional energy sources (like nuclear energy). The interest in solar energy is motivated mainly by the growing awareness of the environmental problems associated with the use of conventional fuels. However, solar energy may become a serious alternative only if it can be used efficiently in major energy consuming industries (like the chemical industry), or be used for electricity generation. Those facilities are nowadays solely dependent on fossil fuels as the prime source of energy. The solar energy, reaching the earth in the form of radiation, can be utilized either by direct quantum conversion using photo-voltaic solar cells, or by converting the radiation into thermal energy, to be used directly for heating, or to feed a thermal to electric converting cycle. After three decades of huge spending on the development of photo-voltaic systems those devices are commercially competitive only on a very small energy scale, while solar thermal commercial applications are more attractive. Prominent examples are the domestic heating water receivers (direct thermal), and LUZ International electricity generation plants which are currently operated on a commercial basis, supplying 80 MWe per plant. Direct thermal exploitation of solar energy is naturally more efficient than converting to electricity, but is limited to specific applications and locations especially since thermal storage at high temperature is not commercially viable. Efficient electricity production at a competitive price is clearly the biggest opportunity for solar energy . (author)
[en] Arrays of fixed discrete surfaces are encountered in a number of important applications. Evaluating radiant heat transfer in an array of fixed discrete surfaces is challenging because array optical properties are often nonhomogeneous and anisotropic. This article presents the results of a Monte Carlo simulation of radiation heat transfer in several array geometries. The results show that for the array geometries included in the study, the extinction coefficient is strongly anisotropic and that optical properties are dependent on both the geometric arrangement of the elements and the scattering characteristics of individual elements. Applications include volumetric air heating solar central receivers, ceramic fabrics, and fibrous insulation
[en] One of the short-term priorities for renewable energies in Europe is their integration for local power supply into communities and energy islands (blocks of buildings, new neighborhoods in residential areas, shopping centers, hospitals, recreational areas, eco-parks, small rural areas or isolated ones such as islands or mountain communities). Following this strategy, the integration of small tower fields into so-called MIUS (Modular Integrated Utility Systems) is proposed. This application strongly influences field concepts leading to modular multi-tower systems able to more closely track demand, meet reliability requirements with fewer megawatts of installed power and spread construction costs over time after output has begun. In addition, integration into single-cycle high-efficiency gas turbines plus waste-heat applications clearly increments the solar share. The chief questions are whether solar towers can be redesigned for such distributed markets and the keys to their feasibility. This paper includes the design and performance analysis of a 1.36-MW plant and integration in the MIUS system, as well as the expected cost of electricity and a sensitivity analysis of the small tower plant's performance with design parameters like heliostats configuration and tower height. A practical application is analyzed for a shopping center with 85% power demand during day-time by using a hybrid solar tower and a gas turbine producing electricity and waste heat for hot water and heating and cooling of spaces. The operation mode proposed is covering night demand with power from the grid and solar-gas power island mode during 14 hours daytime with a maximum power production of 1.36 MW. (Author) 26 refs