Performance evaluation of three solar concentrating cookers

Three solar concentrating type cookers meant for domestic use were tested for their thermal performance and cooking abilities. Stagnation temperature, water heating and cooking tests were conducted. During the tests, the operational ease and problems in each cooker were evaluated.     

Multiple use communal solar cookers

Solar cooking in boarding schools and communal centres in isolated areas demands the heating of large quantities of food. It is generally done in large pots of 30–40 litres. In a previous paper (Saravia et al., Energías Renovables y Medio Ambiente, ASADES, 1999, 6, 7–16), the solar cooker presented consisted of two separate units: a concentrator on one side and an insulated box containing the pot on the other. In this paper we introduce some changes which improve its working capacity. At present we can count on three different kinds of absorbers, which have been optimised to fulfill different functions in a concentrator of an area of 2 m². These alternatives allow the possibility of satisfying the needs of a communal dining centre, cooking for up to 30 children, once each concentrator has been installed.     

Characterisation and design methods of solar cookers

The use of solar cookers is much needed in many regions with good solar radiation intensity throughout the world. The reasons are economical, as the price of fuel for cooking is no longer affordable by many families; ecological, as in many regions deforestation is also associated with the use of wood as an energy source; and social, as the money used to buy fuel could be used to buy food, medications and other needs to improve the quality of life. Because of the variety of solar cookers that has been presented in the literature, a general procedure to compare these cookers with one another is very complex. This article presents the general types of solar cookers, theirs basic characteristics, and experimental procedures to test the different types of solar cookers. The variables measured in these procedures are necessary to calculate parameters, which are used to compare the thermal performance of the solar cookers. In addition to these experimental procedures, a simplified analytical model is presented to design simple cooking systems. For more complex systems, results are shown and references are indicated in the text.     

太阳灶在印度的推广和应用

20多年来太阳灶在印度得到了成功的发展，已经被人们所接受。印度的太阳灶除了应用于炊事方面外，还在其它许多新的领域得到了应用，例如：处理污水，食品加工业，海水淡化，生产蒸汽，农产品干燥；空调和制冷。[编者按]     

浅析太阳能灶在宁夏地区的发展

一引言 宁夏太阳能资源丰富,大部分属于太阳辐射一类区.据资料统计,宁夏每年太阳能辐射量为5781MJ/m2,其空间分布特征是北部多于南部,南北相差约1000 MJ/m2,灵武、同心最大,达6100 MJ/m2以上.宁夏的太阳能辐射量以直接辐射为主,散射辐射少,对宁夏太阳灶的开发利用十分有利.     

Heat loss coefficients for box-type solar cookers

The top and overall heat loss coefficients for the entire feasible operating range of box-type solar cookers are evaluated experimentally and presented in a graphical form as a function of the difference between mean plate temperature and ambient temperature with wind velocity and number of glass covers as parameters.

The range of plate temperatures considered is from 50°C to 180°C. While the wind velocity is varied from 0 to 3.33 m/s, and the number of glass covers considered are from 1 to 4.

Based on these experimental results, a correlation for the determination of top loss coefficient in terms of optical properties of cooker, the spacing between glass cover and absorber plate, wind velocity and number of glass covers, is derived and presented in the paper.     

聚光式太阳灶的设计与制作(Ⅰ)--抛物面聚光太阳灶是怎样工作的

一关于抛物线与抛物面 1什么是抛物线 抛物线是我们在抛出一个物体时,物体在抛力与重力的作用下所运行的路线.如你掷出一个小石子,它飞行的这一段轨迹,就是一条抛物线.抛力的大小不同,抛出的角度不同就会得到不同的抛物线,可惜你通常看不到这条线,我们可画出一条抛物线来先熟悉一下.图1为一个人抛出一颗石子,石子运行的轨迹,就是一条抛物线.     

聚光式太阳灶的设计与制作(Ⅵ)--太阳灶模具的制作

（二）太阳灶灶壳的材料和制作 太阳灶材料可分为灶壳材料、反光材料和支架材料三大部分。由于灶壳材料是关键，我们将重点加以介绍。水泥太阳灶、玻璃钢太阳灶、铸铁太阳灶、菱镁太阳灶等称谓，大都是指灶壳的制作材料而言的，太阳灶灶壳的制作材料对所制作出的太阳灶的特点和优劣以及工艺可行性起到了决定性作用。     

聚光式太阳灶的设计与制作(Ⅶ)--太阳灶模具的制作

（三）反光材料 聚光太阳灶实用效果的优劣，除了设计和制作工艺对太阳灶的影响之外，在很大程度上取决于反光材料的性能。选用反射率高、寿命长的反光材料，能提高太阳灶的热效率。在功率相等的情况下可以使反光面做得小一些，从而有利于操作，也有利于降低成本。     

聚光式太阳灶的设计与制作(Ⅷ)--太阳灶技术要求和测试方法

作为一种产品,我们需要采用科学的方法对它进行检测,以评价它的各项技术指标的优劣.聚光型太阳灶行业标准(NY219-2003),系统地归纳了我国十余年来在聚光型太阳灶方面的科研成果和生产推广经验,提出了太阳灶的设计、型号、规格和测试方法,规定了太阳灶的技术要求、结构检测和性能试验方法,是世界上首次提出的太阳灶标准.为方便读者掌握和应用,我们把标准的主要内容介绍如下.     

聚光式太阳灶的设计与制作(Ⅳ)--选一选太阳灶的支架

针对太阳灶的使用对象主要为农牧民的特点，在满足太阳灶所应具备的功能的前提下，尽量考虑到便于使用和操作，同时还要尽力降低成本。     

聚光式太阳灶的设计与制作(Ⅲ)一一算一算要多大面积画一画灶面轮廓

人们在设计工作中首先遇到的问题，是要做多大面积的太阳灶，让我们首先研究这个问题。     

聚光式太阳灶的设计与制作(V)--太阳灶模具的制作

我们在前面的章节里主要是围绕着抛物面的设计原理与作图法以及结构设计等方面介绍的，现在进入了具体制作阶段，将应用前面学到的知识。     

聚光式太阳灶的设计与制作(Ⅱ)--记一记几个设计参数

一台太阳灶的优劣，同设计参数的选取有着直接的关系，确定合理的设计参数，选择适当的约束条件，是达到优化设计的关键。事实上，太阳灶的设计工作，往往要经过数次参数的调整才会得到令人满意的结果。这些设计参数，在以后还要提到，现在先明确它的含义、选取思路、计算方法及参数间的关系。     

Financial feasibility analysis of box-type solar cookers in India

A framework for financial evaluation of a box-type solar cooker, using cost functions for its capital cost, has been developed. The annual benefits accrued to the user are quantified in terms of number of meals cooked per year and monetary worth of the fuel saved per meal. Expressions for some financial performance indicators have been derived and results of typical numerical calculations are briefly presented.     

Design and development of efficient multipurpose domestic solar cookers/dryers

A truncated pyramid-type solar cooker is designed, fabricated and tested. The truncated pyramid geometry concentrates the incident light radiations towards the bottom and the glazing glass surface on the top facilitates the trapping of energy inside the cooker. One of the salient features of the proposed design is to completely eradicate the need for tracking the sun during cooking, as tracking of sun does not yield better performance. During testing, the highest plate stagnation temperature, under no-load condition, approached 140 °C and under full-load condition, water temperature inside the cooker reached 98.6 °C in 70 min. Two figures of merit, F₁ and F₂, were calculated and their values were 0.117° C m²/W and 0.467 °C l, respectively, meeting the standards prescribed by the Bureau of Indian Standards for solar box-type cookers. Minor modifications in design are recommended to achieve higher temperatures and reduce cooking times. The design also allows trays to be retained for use as a household dryer.     

Mathematical model of the thermal performance of box-type solar cookers

A mathematical model of the heat transfer processes involved with a box-type solar cooker, containing food, was developed. Solar radiation, including that from a flat reflector, enters the box and heat transfer within and out of the box was considered. Using small increments of time, the computer model finds the temperature of the air, food, interior walls and top cover as the solar flux varies throughout the cooking period. Sample results are presented, giving the food temperature as affected by latitude, month, wind, clouds, mass of food, thermal resistance of the box walls and adjustment of the box while cooking.     

The comparison of three types of Indonesian solar box cookers

This paper describes the influences which govern solar box cookers: HS 7534, HS 7033 and the newest design HS 5521. The best of solar cooker, type HS 7033 gave oven temperature of 202°C between 12:00 and 12:45 p.m. on October 7, 1997. Thirty-four units of this type have been field tested since September 1997. It was found that these solar cookers have a good heat storage capability, therefore they can be used for consecutive cooking. The optimization of the size, the aperture area, the insulator thickness, the oven volume and the reflector area leads to a new design, type HS 5521. Its volume is only 35% of the volume of HS 7033 and cheaper. The performance comparison of the last two solar cookers are described based on the data collected during testing with and without load. The HS 5521 has the same heat collection rate and is able to cook as fast as HS 7033.     

Experimental investigation of tracking paraboloid and box solar cookers under Egyptian environment

Two full tracking solar cookers, namely a paraboloid dish solar cooker (PDSC) and a booster mirror solar box cooker (BMSBC) have been designed, constructed and tested during a winter season in Cairo (30° N and 30° E). The cookers are made simple, durable and of low cost. Tests are carried out to compare the performance of these two cookers under the same operating conditions. The results showed that the rate of cooking of the PDSC is higher than that of the BMSBC. Also, the PDSC can handle various types of cooking even under the intermittent sunny and cloudy conditions of the winter.The effect of wind speed on the heat loss from the receiver is of utmost importance for the evaluation of PDSC performance. Therefore, the effect of wind speed on the heat loss coefficients from new or black painted receivers is experimentally determined, analysed and presented in graphical form. The overall heat loss coefficients are correlated in terms of wind speed and surface conditions (painted or unpainted). During the indoor test, the wind speed was varied from 0 to 8 m/s. Based on these experimental results, a wind shield has been designed to reduce the wind effect. Tests confirmed that the wind shield improves the PDSC performance and allows boiling to take place even for high wind speeds. This is confirmed by the thermal analysis which shows reductions of 24 to 35% in the heat loss from the receiver with the presence of the wind shield.     

Evaluating the international standard procedure for testing solar cookers and reporting performance

The international standard procedure for testing solar cookers and reporting performance was proposed at the Third World Conference on Solar Cooking (Avinashilingam University, Coimbatore, India, 6–10 January, 1997) and revised by the committee over the following months. The standard sets limits for environmental conditions, specifies test procedures and calls for performance to be reported in terms of cooking power (W). While this value, like the fuel economy rating of an automobile, is not a guarantee of performance, it does provide a useful tool for comparison. The entire standard is presented in this paper. It was evaluated both by using it to analyze data previously collected and by using it to test one of the solar cookers in the historical data set. The test standard cooking power curve clearly distinguishes between solar cookers of differing design. Estimates of solar cooker performance for different locations and dates are fairly consistent when the test standard is employed. The criteria of being easy to use and presenting data predictive of thermal performance are also satisfied.