Testing of solar cookers and evaluation of instrumentation error

Solar cooking technologies have large potential in developing countries. Many of the solar cookers (particularly box type and parabolic concentrating type solar cookers) have been commercialized in different parts of the world. An effective quality control is essential for a large-scale dissemination of solar thermal technologies on the products being offered by the industry to the end users. For this, there is a need to establish test procedures and methodologies for developing performance characteristic parameters, which could provide an equitable basis for comparison of performances of the products. A comprehensive review of various test procedures of solar cookers has been undertaken in this study.This study presents results of using various test procedures for characterizing box type and a family size parabolic concentrator solar cooker, based on detailed experimental investigations. The study is supported by a number of experiments carried at the location of New Delhi (latitude = 28.56°N, longitude = 77°E) under various climatic and operating conditions round the year. The overall error associated in the determination of performance parameters due to instrumentation has been estimated by using the root-sum square method. It has been estimated that instrumentation cause 1–5.5 percent error on the thermal performance parameters of solar cookers. The effect of instrumentation error has been evaluated maximum on second figure of merit, F₂, optical efficiency factor, F′η_o, and standardized cooking power P_s.     

Experimental testing of a box-type solar cooker using the standard procedure of cooking power

A box-type solar cooker with one (Model I) or four (Model II) cooking pots was constructed and tested under Tanta prevailing weather conditions. Experiments were performed during July 2002 using the cooker with or without load. The obtained results were employed to calculate the two figures of merit, F₁ and F₂, as well as the utilization efficiency η_u and the specific t_s and characteristic t_c boiling times. The obtained values of F₁ indicate that the cooker can be used twice a day for consecutive cooking. F₂ was found to increase almost linearly with the mass of the cooking fluid M_f. The cooker is able to boil 1 kg of water in 15 min when its aperture area equals 1 m². Furthermore, experiments also considered the requirements for the international standard test procedure for solar cookers. The cooking power P was correlated with the temperature difference ΔT between the cooking fluid and the ambient air. Linear correlations between P and ΔT had correlation coefficients higher than 0.90 satisfying the standard. The obtained values of the initial cooking power, heat loss coefficient and the cooking power at a temperature difference of 50 °C agree well with those obtained for small solar cookers. The present cooker is able to cook most kinds of food with an overall utilization efficiency of 26.7%.     

Enhancement the solar box cooker performance using steel fibers

The use of fossil fuel and wood for cooking poses health, environmental, and economic challenges, especially with the growing population. This has led to an increase in the trend towards the use of clean and sustainable cooking sources, including solar cookers. This experimental study aims to contribute by enhancing the performance of a solar box cooker (SBC) according to the concept of porous media via adding steel fibers inside the box as a modified SBC and comparing it with a conventional SBC. The stagnation test to determine the first figure of merit and the load test to determine the second figure of merit, standard boiling time, and cooker optothermal ratio were conducted under the outdoor conditions of Baghdad city. Also, an energy and exergy efficiency analysis, and calculating the rate of heat loss by three water loads heating and cooling tests. The results revealed that the modified SBC has a higher thermal performance than the conventional SBC.     

Fabrication of and performance studies on a low cost solar cooker having an inclined aperture plane

A low cost box-type solar cooker made of two paper carton boxes with crumpled newspaper balls as insulation has been fabricated with a tilted aperture plane. Comparative tests of this cooker have been conducted against a normal type costlier solar cooker with 1000 ml load of water in each of the cookers. It has been observed that on a sunny day water temperature initially increases more rapidly in the new cooker compared to the normal type cooker. But at temperatures higher than 90°C both the cookers perform similarly. Two figures of merit F₁ and F₂ have also been found to be satisfactory. An arrangement of low cost auxiliary heating using a 100w electric bulb inside a blackened metal casing allows the carton box cooker to reach cooking temperatures under cloudy conditions with ease when the normal type solar cooker fails. The cost of materials for the new cooker is within US $10 and has been observed to be as effective as the normal type solar cooker which requires between US $40 and $65 to fabricate.     

Users and disusers of box solar cookers in urban India—: Implications for solar cooking projects

The purpose of this study is to understand the reasons behind the continued use or disuse of solar cookers, and to outline the implications from the results of this study for future solar cooker projects. Twenty-eight families in three urban sites in Gujarat, India who have a solar cooker have been interviewed. Their experience with solar cookers and solar cooking is studied. Direct discussions with families who have practical experience with solar cooking, brings forth significant practical issues. The study shows that many disusers of solar cookers do not have a suitable place for their solar cookers. Other disusers could not adjust their daily routines with what solar cooking requires, and some disused their solar cookers because they were not interested in using them. Both objective factors and aspects of practical interest have been shown to be important issues for understanding the conditions of prospective users and the shaping of the projects and the relevant technologies. It is concluded that project developers should consider the potential users as an important partner in project development processes. For example project developers can by close dialogue with them, uncover and define practical parameters which have important bearing on higher usability of solar cookers.     

Fast thermal cycling of acetanilide and magnesium chloride hexahydrate for indoor solar cooking

Solar cookers are broadly divided into a direct or focusing type, indirect or box-type and advanced solar cookers. The focusing and box-type solar cookers are for outdoor applications. The advanced solar cookers have the advantage of being usable indoors and thus solve one of the problems, which impede the social acceptance of solar cookers. The advanced type solar cookers are employing additional solar units that increase the cost. Therefore, the solar cooker must contain a heat storage medium to store thermal energy for use during off-sunshine hours. The main aim of this study is to investigate the influence of the melting/solidification fast cycling of the commercial grade acetanilide C₈H₉NO (T_m = 116 °C) and magnesium chloride hexahydrate MgCl₂·6H₂O (T_m = 116.7 °C) on their thermo-physical properties; such as melting point and latent heat of fusion, to be used as storage media inside solar cookers. Five hundred cycles have been performed. The thermo-physical properties are measured using the differential scanning calorimetric technique. The compatibility of the selected phase change materials (PCMs) with the containing material is also studied via the surface investigation, using the SIM technique, of aluminum and stainless steel samples embedded in the PCM during cycling. It is inferred that acetanilide is a promising PCM for cooking indoors and during law intensity solar radiation periods with good compatibility with aluminum as a containing material. However, MgCl₂·6H₂O is not stable during its thermal cycling (even with the extra water principle) due to the phase segregation problem; therefore, it is not recommended as a storage material inside solar cookers for cooking indoors. It is also indicated that MgCl₂·6H₂O is not compatible with either aluminum or stainless steel.     

Solar cookers for outdoors and indoors

The solar cooking process has been investigated to develop safe, simple, portable, and reliable solar cookers. The concept of insulated and vapor-tight pots has been introduced and applied to oven, point-focus and heat-pipe cookers. A new, flat-plate cooker with heat pipes has been developed. It requires no tracking and allows cooking to be done in the shade or indoors. Also, a novel-portable cooker, the Mina Oven, featuring a vapor-tight pot and an integral collector with reflector flaps, has been constructed and tested. A second portable cooker that has been developed is the Arafa Cooker, which comprises a parabolic dish focused at a glazed and insulated receiver. Experiments indicated that all cookers yielded satisfactory performance, with cooking times of 25–45 min per kg of food per m² of solar collection area while operating from 10 a.m. to 4 p.m.     

A review of the thermal performance parameters of box type solar cookers and identification of their correlations

One of the many thermal performance parameters such as efficiency, cooking power, figures of merit etc. are used to evaluate a solar cooker (including box type) based on test procedures which are non-identical. In the absence of an interrelation between the different performance parameters, it is very difficult to compare the cookers’ performance reported by different researchers and establish the criteria required for selection of a cooker which can accomplish cooking successfully and satisfactorily. In this review paper, some of the performance parameters and the related test procedures have been reviewed for box type solar cooker. Further an attempt has been made to identify common links between the different performance parameters in terms of a few objective parameters. This provides an enabling tool to the researchers to compare and correlate the different performance parameters. Three such objective parameters have been identified for box type solar cookers.     

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.     

Parametric model of solar cooker performance

This paper presents a model for prediction of the cooking power of a solar cooker based on three controlled parameters (solar intercept area, overall heat loss coefficient, and absorber plate thermal conductivity) and three uncontrolled variables (insolation, temperature difference, and load distribution). The model basis is a fundamental energy balance equation. Coefficients for each term in the model were determined by regression analysis of experimental data. The model was validated for commercially available solar cookers of both the box and concentrating types. The valid range of model application includes most of the feasible design space for family-sized solar cookers. The model can be used to estimate the cooking capacity of existing box type and concentrating type solar cookers. It can also be used to find the combinations of intercept area and heat loss coefficient required to cook a given quantity of food in a given climate.     

Novel solar cookers: suitable for small families

This paper presents the fabrication details and on-field experimental studies of two novel solar cookers, suitable for cooking requirements of small families; these are named as small family solar cookers (SFSC-1 and SFSC-2). Small size, good thermal performance, light weight, low-cost and short payback periods are some important features of these cookers. The values of some essential thermal performance parameters, first figure of merit (F₁), second figure of merit (F₂) and standard cooking power suggested by Bureau of Indian Standards and International Standard for box-type solar cookers, have been evaluated by experimental studies and found to be 0.116°C m²/W, 0.466, 30 W and 0.118°C m²/W, 0.488, 50 W for SFSC-1 and SFSC-2, respectively. A comparative analysis of the thermal performances of SFSCs with the solar cookers, developed by many authors, has also been presented here. The payback periods with respect to different cooking fuels for SFSCs have been found to be reasonably short.     

The development impact of solar cookers: A review of solar cooking impact research in South Africa

Solar cooking is often considered “a solution looking for a problem”. Solar cookers have long been presented as an interesting solution to the world's problem of dwindling fuel wood sources and other environmental problems associated with wood fuel demand for cooking. However, recent GTZ field work in South Africa showed different benefits instead: the use of solar cookers resulted in appreciable fuel and time savings as well as increased energy security for households using commercial fuels. These observations are based on field tests in South Africa that started in 1996 to investigate the social acceptability of solar cookers and to facilitate local production and commercialisation of the technology. Impact studies and use rate studies have been carried out by a number of different organisations since the inception of the project and although commercialisation of the technology has not been achieved to its fullest potential, impact studies indicate that solar cookers have a positive development impact on households through fuel-, energy- and time savings. The article aims to summarise the findings of the various studies and present an overview of use rates and impact data. A variety of factors influence solar cooker use rates, which in turn determine impacts. Some factors are related to the user, some to the environment in which the cooker is used and some to the cooker itself. Ultimately, the data shows that on average, only 17% of solar cooker owners do not use their stoves after purchase and that active solar cooker users utilise their stoves on average for 31% of their cooking incidences. Since the majority of solar stove buyers actually use their stoves and obtain real benefits, this suggests that that solar cookers are indeed not a solution looking for a problem but a solution worth promoting.     

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.     

Performance test of a box‐type solar cooker: effect of load on the second figure of merit

In this paper thermal performance test experiments for first figure of merit (without load) and second figure of merit (with load) of a box‐type solar cooker were conducted as per Bureau of Indian Standards. The values of second figure of merit (F₂) were determined for different loads of water and the results show that F₂ depends on the quantity of water loaded in a solar cooker. Therefore, it is recommended that the performance test method should specify the amount of water which is to be taken. Copyright © 1999 John Wiley & Sons, Ltd.     

On-line recording of solar cooker use rate by a novel metering device: Prototype description and experimental verification of output data

A metering device for the determination of solar cooker use rate is presented. The device records food temperature, ambient temperature and irradiance. Automatic data evaluation yields the number of cooking cycles, cooking time, food “thermal mass”, as well as the impact on fuel consumption and GHG emission compared to other cooking techniques. Metering results are compared with actual conditions for box-type and concentrating solar cookers and found to be in agreement.     

A new solar cooker design

This paper deals with a new box-type solar cooker design with a single reflector at the hood. In this design, the base of the oven acts as the lid, unlike the conventional box-type solar cooker. With the introduction of this concept of the lid as the base of the oven, we solve the problem of preheating, as faced in the conventional box-type solar cooker. Thus, the performance of conventional box-type solar cookers can be appreciably improved by having the lid at the bottom of the oven and not at the top. It has been observed that, having cooked once, the preheating time for further cooking is greatly reduced as compared to the conventional box type. Hence, cooking twice a day by this cooker becomes easier, unlike cooking by the conventional one.     

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.     

Top heat-loss factor of double-glazed box-type solar cooker from indoor experiments

The top heat-loss factor (U_t) of a box-type solar cooker varies with plate temperature, wind heat-transfer coefficient and ambient temperature. A method for correlating U_t with these variables is presented for a cooker with double glazing. A set of equations is developed for correlating data obtained in indoor experiments at different plate temperatures and wind speeds.     

Heat losses from a paraboloid concentrator solar cooker: Experimental investigations on effect of reflector orientation

The thermal performance of any focussing-type solar cooker, where an unglazed/uuninsulated cooking pot is often used, depends to a great extent on wind conditions. Moreover, these cookers need frequent adjustments to track the Sun in order to keep the focus always at the bottom of the cooking pot. The present paper reports experimental investigations on heat losses from such cooker for different orientations of the paraboloied reflector. Values of the heat loss factor for the tilted reflector are compared with those obtained with the reflector in a horizontal position. The heat loss factore for a cooker with/without reflector is determined for no-wind conditions. It is suggested that a paraboloid reflector is not required for heat loss determination in this case.