Studies on a new combined concentrating oven type solar cooker

This paper describes a combined concentrating/oven type solar cooker. The device can be used for cooking, boiling and roasting of foods on clear days. The cooker makes use of both concentrator and flat-plate collector principles, wherein the sunlight entering the cooker is reflected onto a hood which is provided with a selective solar absorber coating which houses the cooking vessels. Hence, the cooker makes use of both direct and diffuse solar radiation. The important part of this new device is a stationary mode and maximum capture of energy through improved design. The new cooker has been found to be more practical in comparison with either the simple hot box type solar cooker or concentrator type cookers where one needs to direct it to follow the sun. The cooking trial shows that the new device can be used twice a day, even on winter days.     

Performance and testing of large-size solar water heater cum solar cooker

The performance of a novel device has been tested. The device can be used as a collector cum storage type solar water heater during the winter, and, with minor adjustments, it can be used as a hot-box solar cooker. The device can provide hot water at 50–60°C in the evening, which can be maintained at 40–45°C until the following morning. It can also be used for cooking food for about 40 people. The efficiencies of the device as a solar water heater and as a solar cooker have been found to be 67.7% and 29.8%, respectively. The payback period varies between 1.64 to 5.90 years depending on the fuel it replaces. The payback periods are of increasing length with respect to the fuels firewood, coal, electricity, LPG and kerosene.     

Design optimization of solar cooker

Various designs of solar cookers have been theoretically investigated with a view to optimize their performance. Starting from a conventional box type cooker, various combinations of booster mirrors have been studied to arrive at a final design, aimed at providing a cooker, which can be fixed on a south facing window (for countries of northern hemisphere, mainly situated near the tropic of Cancer). This cooker, with a rear window opening, may provide higher cooking temperature for a fairly large duration of the day. Two or three changes in positions of the side booster mirrors, without moving the cooker as a whole has been proposed. The new design has been experimentally implemented and compared with a conventional box type solar cooker. Besides the convenience of a rear window opening, the cooker provides temperatures sufficiently high to enable cooking two meals a day.     

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.     

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.     

An improved solar cooker

An improved hot box type solar cooker (SC-2) has been designed, developed and tested. It is an improvement on the solar cooker SC-1 earlier developed at the institute. The cooking chamber has properly been optimized for cooking the food for a family of five persons. A rubber gasket has been provided at the boundary of the openable door to prevent the leakage of hot air, thus increasing the pressure in the cooking chamber. Different cooking trials like boiling, roasting and baking were successfully conducted and the cooker was found useful from 8.00 a.m. to 5.00 p.m., even during a winter month. The efficiency of the cooker was found to be 41.2 per cent.     

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.     

Design and development of a solar cooker cum drier

A solar cooker cum drier has been designed and developed. In designing this unit, optimum booster-collector geometry has been considered in order to eliminate the requirement of sun tracking. Tilting arrangements have also been provided to capture more solar energy. This dual purpose device has been found useful for cooking food and dehydrating fruit or vegetables.     

Thermal performance of a solar pressure cooker based on evacuated tube solar collector

This paper presents the thermal performance of a community type solar pressure cooker based on evacuated tube solar collector. The developed design of solar pressure cooker has separate parts for energy collection and cooking unit and both are coupled by heat exchanger. The paper has presented the performance results of experimental study conducted on solar pressure cooker and a simulation model has been developed for predicting the cooker performance under a variety of operating and climatic conditions. The theoretical model is validated against the experimental results. The obtained results have suggested a possibility of several batches of solar cooking on a clear sunny day under typical conditions of Delhi.     

Solar cooker with latent heat storage systems: A review

Cooking with the sun has become a potentially viable substitute for fuel-wood in food preparation in much of the developing world. Energy requirements for cooking account for 36% of total primary energy consumption in India. The rural and urban population, depend mainly, on non-commercial fuels to meet their energy needs. Solar cooking is one possible solution but its acceptance has been limited partially due to some barriers. Solar cooker cannot cook the food in late evening. That drawback can be solved by the storage unit associated with in a solar cooker. So that food can be cook at late evening. Therefore, in this paper, an attempt has been taken to summarize the investigation of the solar cooking system incorporating with phase change materials (PCMs).     

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.     

Thermal performance of a solar cooker integrated vacuum-tube collector with heat pipes containing different refrigerants

A solar cooking system using vacuum-tube collectors with heat pipes containing a refrigerant as working fluid has been fabricated, and its performance has been analysed experimentally. The experiments were conducted during clear days in July and August of 2002 in Elazı , Turkey under similar meteorological conditions for three refrigerants and water. Detailed temperature distributions and their time dependences were measured. The maximum temperature obtained in a pot containing 7 l of edible oil was 175 °C. Also, the cooker was successfully used to cook several foods. The cooking processes were performed with the cooker in 27–70 min periods.     

Design, development and testing of a double reflector hot box solar cooker with a transparent insulation material

A double reflector hot box solar cooker with a Transparent Insulation Material (TIM) has been designed, fabricated, tested and the performance compared with a single reflector hot box solar cooker without TIM. A 40 mm thick honeycomb made of polycarbonate capillaries was encapsulated between two glazing sheets of the cooker to minimise convective losses from the window so that even during an extremely cold but sunny day two meals can be prepared, which is not possible in a hot box solar cooker without TIM. The use of one more reflectors resulted in an avoidance of tracking towards sun for 3 h so that cooking operations could be performed unattended, as compared to a hot box solar cooker where tracking ahead of the sun is required every hour. The efficiencies were 30.5% and 24.5% for cookers with and without a TIM respectively, during the winter season at Jodhpur. The energy saving by use of a solar cooker with TIM has been estimated to be 1485.0 MJ of fuel equivalent per year. The payback period varies between 1.66 and 4.23 y depending upon the fuel it replaces, and is in increasing order with respect to the following fuels: electricity, firewood, coal, LPG and kerosene. The estimated life is about 15 y. Therefore, the use of a solar cooker is economical. The double reflector hot box solar cooker with TIM will be a boon in popularising solar cookers in developing countries.     

The performance of a box-type solar cooker with auxiliary heating

In Bangladesh it is very difficult to use solar cookers during the months when the days are generally cloudy and at times solar cooking becomes impossible. To overcome such problems for a box-type solar cooker, we have used an auxiliary source of energy inside it. This is done with the help of a built-in heating coil inside the cooker or a retrofit electric bulb in a black painted cylinder. It is found that the use of auxiliary sources allows cooking on most cloudy days.     

Design, development and testing of a large-size solar cooker for animal feed

A large-size solar cooker for animal feed has been designed, developed and tested. The cooker employs locally available materials of low cost, e.g. pearl-millet husk and horse excreata. The commercial materials required for its fabrication are plain glass, mild steel angle and sheet, wood and aluminium sheet cooking utensils. The solar cooker is capable of boiling 10 kg of animal feed, sufficient for five cattle per day. The efficiency of the solar cooker is 21·8%. The cost of the cooker is only Rs 1200, which can be recovered in 0·45-1·36 years depending upon the fuel it replaces. The short payback periods suggest that the use of the solar cooker is economic. The use of the cooker will save a lot of firewood, cowdung cake and agricultural waste which are presently used for the boiling of animal feed.     

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.     

Fabrication of portable solar thermal bank for indoor cooking

The aim of this report is to build a portable solar thermal bank based on a Scheffler reflector that is capable of boiling-type cooking using HITEC as a thermal storage material. This report reviews the problems related to solar cooking and evaluates the novel layout of a portable solar thermal bank which includes a daily thermal storage vessel. This stove is in the shape of a cylindrical container filled with phase-changing latent heat storage material. Inside the container, we provide a small gap taking into account the volumetric expansion of the phase change material (PCM) during the melting process. The solar thermal bank is charged in the sun. It is placed directly for a few hours under the focus of a Scheffler reflector, which charges the solar thermal bank with enough thermal energy stored. After a while, the cooking process can be completed by users using that stored heat. The top cavity is used as a cooking pot in a solar thermal bank. Cooking meals do not require direct sunlight, which is typical for most solar cookers. The portable solar thermal bank is an alternative for low-income households and adapts to local traditions of indoor cooking. It is portable and can be used safely to cook indoors or outdoors. In this study, a solar cooker with a thermal storage device was developed using a PCM. The size of the stove has been calculated by calculating the energy consumption for two to three people. HITEC salt has been chosen as a phase change material for thermal storage, which will be used for cooking when there is no sunlight. It enhances the applicability of solar cooking and preserves cooking possibilities using energy stored throughout the day at low production costs.     

The performance of a low cost clay solar cooker

This paper reports the development of a low cost clay solar cooker. The main features of this cooker are that it is made from cheap, locally available materials, and needs no skilled labour. One of the new design features of the solar cooker is the replacement of the absorber plate with locally available black sontes. The effects of using the black stones instead of the abrosber plate resulted in solar cooker capable of storing solar energy, hence making late cooking possible.     

Evaluating the optimum load range for box-type solar cookers

This paper introduces a new concept of Optimum Load Range (OLR) for solar cookers. OLR gives the load values for which cooker preferably shows good thermal as well as good cooking performance; it may be considered a crucial parameter for solar cookers. This OLR concept is based on the dependence of rate of rise of load temperature on different heat transfer processes between load and cooker interior. This concept illustrates solar cooking in two simple steps. The total time required to complete these steps puts an essential constraint for cooking of any load amount. The maximum value of load (upper limit of OLR) till which cooker shows satisfactory cooking may be determined from this constraint. This constraint requires determination of two OLR parameters which are t_{step I} and t_{step II}. The load for which cooker remain almost 30% efficient, may be referred as lower limit (minimum value) of OLR. For the verification of OLR, experimental studies have been conducted with a solar cooker named SFSC. The OLR parameters along with different thermal performance parameters (TPPs) (second figure of merit (F₂), utilization efficiency (η_u) etc.) suggested by different researches for solar cookers in water load condition have been computed from the measured thermal profiles of different loads (0.8–3.0 kg). From the curve analysis of different TPPs with load, the existence of upper limit of OLR is observed. The values of rate of rise of load temperature at water temperatures 80, 85 and 90 °C for different loads also confirm the same. The OLR of SFSC is found to be 1.2–1.6 kg.     

Solar cookers—part-II—cooking vessel with central annular cavity

Cooking vessels used in a solar cooker must be able to transfer the heat trapped in the cooker effectively to the food material. In the preceding paper (Part-I) the advantage of keeping the vessel on lugs was discussed. In the current paper the performance of a cooking vessel with a central annular cavity kept on lugs is discussed. The experiments were conducted for several days using water and thermic fluid as working medium. The studies indicated that the cooking vessel with central annular cavity on lugs performs much better than the conventional vessel kept on the floor of the cooker. The conventional vessel is considered to be the benchmark for the purposes of comparison.