Design theory and performance analysis of paraboloidal solar cooker

A paraboloidal collector having aperture diameter 1.3 m, depth 0.30 m, and focal length 0.35 m was designed and fabricated. The paraboloidal solar cooker was tested under no-load conditions at a recorded maximum temperature of 326°C. The analysis was made from the sensible heating and cooling curves. The values of the overall heat loss factor (F′ UL) obtained from the sensible cooling curve were smaller on different days. The minimal heat loss was due to the wind shield provided at the paraboloidal receiver. Analysis of the sensible heating curve gave the values of the optical efficiency factor (F′ η₀). The performance of the paraboloidal collector was determined, and the thermal efficiency was found to be 26%. The performance curve was plotted to predict the approximate time required to boil a known amount of water under given climatic conditions. The solar cooker was found to be useful in cooking a variety of foods.     

Performance enhancement of parabolic trough collectors by solar flux measurement in the focal region

Characterization of the optical performance and detection of optical losses of parabolic trough collectors are very important issues in order to improve the optical efficiency of these systems and to ensure the desired quality in solar power plants. Therefore two methods of measuring the solar flux in the focal region were developed: PARASCAN (PARAbolic Trough Flux SCANner) is a solar flux density measurement instrument which can be moved along the receiver axis. The sensor registers the flux distribution in front and behind the receiver with high resolution. The resulting flux maps allow to calculate the intercept factor and to analyse the optical properties of the collector at the finally interesting location, i.e. around the receiver. The camera-target-method (CTM) uses a diffuse reflecting Lambertian target and a calibrated camera which takes pictures of it. The target is held perpendicular to the focal line surrounding the receiver. With the resulting images of this fast and easy method it is possible to visualize the paths of the reflected rays close to the receiver and to detect local optical errors. Both methods are described in detail. Latest measurement results gained at the Eurotrough-II prototype collector built on the Plataforma Solar de Almería (PSA) in Spain are presented and consequences are discussed.     

Cost of paraboloidal collectors for solar to thermal electric conversion

Much is underway concerning technical and design aspects of solar collectors and associated costs of point designs. But little has been published on the tradeoffs between alternative designs and large-scale manufacturing possibilities. To fill this gap, close interchange is needed among those versed in technical and systems design, manufacturing and costing. The solar to thermal electric power study funded by the National Science Foundation and carried out by Colorado State University and Westinghouse Electric Corporation has led to the assembly of such a team. This team is obtaining new data on large-scale production of concentrating collectors of widely varying parameters.

Investment and other costs of paraboloidal collectors with various aperture widths, reflectivities, rim angles, and accuracies of contour and tracking are reported herein. In studying alternative design-cost-performance relationships, emphasis is placed on breadth of coverage rather than on detailed accuracy. Alternative aperture widths led to preferences for different production processes that are not particularly sensitive to changes in rim angle or reflectivity. Significant cost relationships in the manufacture, installation and maintenance of collectors were found; other relationships are less certain. Besides the above, study results indicate directions for further study.     

碟式聚光器卸风载数值研究

文章以太阳能热电系统中的碟式聚光器为研究对象,使用ANSYS CFX 14.0仿真软件,采用SST k-ω湍流模型,该模型比例为1∶1,对蝶式聚光器开缝卸风载的特性进行数值仿真。首次提出了开缝面积比和卸载率两个参数,并计算了不同风速、俯仰角、开缝面积比以及开缝位置情况下,单环缝、等缝宽多环缝以及等面积多环缝的卸风载效果。研究结果表明:当俯仰角为57.5°时,无缝蝶式聚光器所受到的风载最大,而开缝能够有效地降低风载;当开缝面积比为3%,且开缝位置位于碟盘开口半径1/3处时,等面积多环缝的卸风载效果最优。     

A novel application of a Fresnel lens for a solar stove and solar heating

This paper presents a novel design and the prototyped solar cooking stove which uses a large Fresnel lens for the concentration of sunlight. The technology demonstrates high safety and efficiency of solar cooking and heating using Fresnel lenses which are low cost and available from off-the-shelf. The stove has a fixed heat-receiving area located at the focal point of the lens. The sunlight tracking system rotates the Fresnel lens about its focal point in both zenith and azimuth angles. The tracking is accomplished through a revolving motion of two rotation arms that hold the lens and a horizontal rotation of a platform that the lens system stands on. The rotation of the arms tracks the sunlight in zenith plane, while the rotation of the platform tracks in the azimuth plane. Since the solar tracking allows the Fresnel lens to concentrate sunlight to a fixed small heat-receiving area, relatively low heat loss and high energy efficiency is made possible. The heat is used to maintain a stovetop surface at temperatures around as high as 300 °C, which is practical for cooking applications in a very safe, user-friendly, and convenient manner. The system also demonstrates the possibility of transferring heat using a working fluid for indoor heating and cooking. Wider applications using the system for solar thermal collection and utilization are also undergoing development.     

Numerical modelling of wind and dust patterns around a full-scale paraboloidal solar dish

This study reports on numerical predictions of velocity and pressure fields, and dust particles trajectories in steady and unsteady flows around a full-scale paraboloidal solar dish. Calculations are performed for three wind speeds of 4.16, 9.72, and 15.2 m s⁻¹, and dish pitch angles from 0° to 180°. The flow field structure, lift and drag coefficients are calculated for each flow configuration. Using the predicted mean flow velocity field, analytical expressions for the aerodynamic coefficients, as a function of the pitch angle, are developed. The unsteady-state flow is characterised by formation of stable vortices behind the dish for most flow configurations, except at 60° and 150° pitch angles. At these angles vortex-shedding occurred with a strong flow oscillation extending downstream the dish. The calculations of dust particles trajectories provide a qualitative assessment of the deposition rate, dish orientation, and surface locations where dust accumulation is most likely to occur. The study also presents an initial assessment of the effectiveness of various windbreaks installed upstream of the dish in reducing aerodynamics drag.     

Energy distribution on the focal plane of a parabolic cylindrical concentrator with angular defocusings

The concentrating capability of an ideal parabolic cylindrical reflector that is exposed to collimated radiation flux with longitudinal and transverse angular defocusings is examined. The energy distribution on the focal plane of the concentrator is studied.     

平面真空玻璃作箱式太阳灶透明盖板的实验研究

介绍了用窄缝高真空平面玻璃作普通工太阳灶的透明盖板,对箱式太阳灶的集热性能进行了实验研究的结果,并与用普通双层玻璃作盖板的箱式太阳灶进行了对比,发现用平面真空玻璃作盖板能够显著改善箱式太阳灶的性能。     

Thermal analysis in the focal spot of a solar furnace

The paper deals with the analytical determination of time dependent temperature distribution in a sample placed in the focal plane of the paraboloidal mirror of a solar furnace. Several different heat pulses are considered and some graphs are shown.     

Experimental investigation of high temperature congregating energy solar stove with sun light funnel

A solar stove which uses a light funnel to guide light and congregate solar energy has been designed. Its structure and operation principle have been introduced. The performance tests under the real weather have been carried out and the graphic lines of experiment have been given. The experimental result shows that the maximum temperature inside the stove is as high as 250 °C under the condition of 1.5 m² of lighting area, 70% reflectivity of reflecting aluminum foil inside surface of concentrator and no load (without water inside the coil pipe). When reflectivity is 86% the heat collecting efficiency of the device is about 43%. The collecting power that the stove receives can be up to 500 W. It is an ideal medium and high temperature solar energy congregating device suitable for industrial usage or cooking and other domestic usage.     

Geometric Brownian distribution of solar radiation with an economic application

This paper presents the results of a recent model by Hamlen and Hamlen[1] which uses a distributed lag model to predict local levels of incoming solar radiation. The results indicate that the daily levels display a geometric Brownian motion. This distribution was introduced by Professor Samuelson[2] to explain the movement in stock prices over time. It modifies the more familiar arithmetic Brownian motion to eliminate the problem of negative values of the predicted stock prices with a high probability. Solar radiation, kike stock prices, cannot take on negative values and requires the geometric Brownian motion. The distribution is introduced and parameters of the distribution are given for twenty-two cities in the U.S.

The results are then applied to the problem of determining economically efficient combinations of heating technologies given a solar heating system and a conventional backup system. A production function for heat is developed that results in a stochastic function with two random variables: available solar radiation and outside temperature. This, in turn, results in a chance constrained cost minimization problem.     

Statistical study of solar radiation information in an equatorial region (Singapore)

Results of regression analysis relating total solar radiation with common meteorological factors, based on data from Singapore, are summarized. The regression coefficients are found to be unstable over different periods of time, producing poor radiation estimates. A set of useful statistical properties of measured radiation data is next presented, showing the expected number of days in a year and in a given month of the year in which daily total radiation falls within a given range of values, and also the frequencies of occurrence of periods of successive days in which radiation is below specified values. Probabilistic limits of figures are also given to enable designers and users of solar energy utilization systems to perform calculations based on ranges of possible values, rather than point estimates, of amounts of expected radiation.     

The flux through the focal spot of a solar furnace

An analysis is made of the flux through the focal spot of a solar furnace, taking into account the limb darkening of the sun.     

Prospects of solar hydrogen production in the Adrar region

The region of Adrar, is one of the most remote and the most deprived regions in Algeria. The development of this region requires the exploitation of its natural resources more particularly of its solar and wind energy resources. However, the exploitation in an effective and viable way of these huge natural resources requires the conversion of these sources of energy into an energy vector that is versatile in its use, storable, transportable and ecologically acceptable. Solar hydrogen seems to be the best candidate today.In the present work, the meteorological and radiometric data of the region are examined. A system of PV–electrolyzer system of solar hydrogen production is proposed. An estimate of the solar hydrogen potential and its production cost are carried out. Finally, the results are discussed.     

Determination of photo-active region in organic thin film solar cells with an organic heterojunction

The photo-active region in the solar cells consisting of Cu-phthalocyanine (CuPc) and perylene-derivative (PV) layers was determined by using exciton blocking layers (EBLs) inserted in these layers. The photocurrent density was low when the EBL was placed near the CuPc/PV interface. With the increase of the distance between the EBL and the CuPc/PV interface, the photocurrent increased. However, when the distance reached a certain value, it leveled off owing to the limited diffusion length of excitons. From the analysis of the relationship between the position of EBL and the photocurrent density, the photo-active regions in the CuPc and PV layers were estimated to be 8 and 12 nm thick from the interface, respectively.     

Laminar flow distribution in solar systems

This work investigates the isothermal and non-isothermal laminar flow distribution through water solar systems. Reverse, as well as direct return circuits are studied. First and second order algebraic equations were developed for isothermal and non-isothermal, fully developed laminar flow distribution, taking into consideration experimental results on junction pressure losses. The effect of the various parameters appearing in the derived equations is also investigated. The flow uniformity was found to be greater in reverse return circuits rather than in centrally-fed direct return circuits.     

Short-circuit current distribution in solar cells

This paper describes a method to determine the contribution of each region of a solar cell to the short-circuit current, using spectral response measurements and dynamic inner collection efficiency (DICE) analysis. The photon flux is calculated along the perpendicular axis of the cell surface at a given illumination condition, normally AM0 or AM1. This enables to calculate the current at each surface-parallel plane for which the DICE parameter is known. The method is applied to silicon solar cells to exemplify its capability.     

Estimation of global solar radiation in the Indonesian climatic region

In this paper the monthly average daily global solar radiation correlation applicable to the Indonesian climatic region is presented. The correlation developed is based on the meteorological data collected from seven meteorological stations, namely: Banjarbaru, Denpasar, Jakarta, Kupang, Manado, Palembang and Semarang. The correlation developed evolves from the Sayigh's “Universal Formula” with a slight modification in the form of a correction factor (I_CF) to suit the Indonesian climatic conditions.     

Energy balances in double-effect wick-type solar distillers

The theory of single-effect wick-type solar distillers has been extended to that of double-effect devices by using appropriate energy balances. The performance of double-effect solar distillers may be evaluated under various conditions by solving the theoretical energy-balance equations.