Experimental comparison of a DC PV cooker and a parabolic dish solar cooker under variable solar radiation conditions

Solar cookers are not all-weather cooking devices and operate poorly during cloudy and low sunshine conditions. Their performance is evaluated usually during high solar radiation conditions. The objective of this study is to compare two solar cookers under variable non-ideal weather conditions. The comparison is carried out under variable solar radiation conditions to compare the all-weather performance of these two cookers. This is a major novelty compared to previous work reported where solar cookers are tested under high and ideal solar radiation conditions. Experiments to compare a PV DC battery-powered solar cooker and a parabolic dish solar cooker are presented in this paper. A total of six water heating tests are carried out to comprehensively compare these two types of solar cookers under different solar radiation conditions. Also, four food cooking tests are carried out with different types of food. The PV solar cooker shows almost constant input electrical power in the range of 160–180 W during the experimental tests whereas the input thermal power for the parabolic dish is highly variable depending on the solar radiation conditions (200–1200 W). The output water heating powers obtained using the PV cooker (66–100 W) are comparable to those obtained with parabolic dish solar cookers (78–142 W), regardless of the significantly lower input heating power. Water is boiled in all the heating tests with the PV cooker, whereas water is boiled for tests with low solar radiation variability for the parabolic dish solar cooker. Higher water heating efficiencies within a small range (0.38–0.57) are obtained for the PV cooker compared to the parabolic dish solar cooker (0.11–0.42). The water heating efficiency of the parabolic dish solar cooker is highly affected by ambient solar radiation and windspeed conditions. Food was well cooked with the PV cooker in all four food cooking tests, whereas food in only two tests with low solar radiation variability was well cooked for the parabolic dish solar cooker. The PV cooker proves to be an all-weather cooker from the experimental results obtained. Future work will extend the use of the PV system for other domestic applications such as lighting and refrigeration together with solar cooking for a multipurpose DC decentralized system for communities without grid connectivity

Performance comparison of two solar cooking storage pots combined with wonderbag slow cookers for off-sunshine cooking

Two similar storage cooking pots are experimentally evaluated and compared during solar cooking and storage off-sunshine cooking periods. One storage pot has sunflower oil as the sensible heat storage material, while the other has erythritol as the phase change material (PCM). To test their thermal performance during off-sunshine periods, the two pots are placed in insulated wonderbag slow cookers. Water and sunflower oil are used as the cooking fluids in the experimental tests. The sunflower oil cooking pot shows better performance during the solar cooking periods since it shows shorter cooking times (1.8–5.6 h) compared to the erythritol PCM pot (3.8–6.6 h). The sunflower oil pot also attains higher maximum storage temperatures (124–145 °C) compared to the erythritol PCM pot (118–140 °C). Storage efficiencies for the sunflower oil pot (3.0–7.1%) are also greater than those of the PCM pot (2.5–3.7%). During the storage cooking periods, the erythritol based phase change material cooking pot shows better performance as evidenced by the lower temperature drops (0.1–9.7 °C) from the maximum cooking temperatures compared to 8.3 to 34 °C for the sunflower oil pot. The heat utilisation efficiencies for the erythritol pot (4.8–14.3%) are also greater compared to the sunflower oil pot (3.7–6%)

Investigation of In–48Sn as a phase change material candidate for thermal storage applications

Latent heat storage systems provide large thermal storage densities for solar energy storage for various domestic and industrial applications. In–48Sn, an alloy of indium and tin a lead-free solder is investigated as a phase change material (PCM) in latent heat storage systems for heating applications. Results obtained from differential scanning calorimetry indicate that the alloy is useful in storing sensible heat beyond its melting temperature as it exhibits very little decomposition up to 400 °C. Though In–48Sn possesses a low latent heat of fusion, its high density allows for a larger thermal storage mass. The behaviour of In–48Sn in a 50 mm aluminium spherical capsule during charging and discharging cycles is investigated using sunflower oil as the heat transfer fluid (HTF) at flow rates of 3, 6, 9 and 12 ml/s. The influence of the charging temperature on the charging characteristics of the encapsulated PCM is also investigated. The average charging and discharging rates of the encapsulated PCM show an increase with an increase in the HTF flow rate. The HTF temperature determines the maximum temperature attained by the PCM and thus the total energy stored by the encapsulated PCM. In–48Sn shows good potential as a PCM in a spherical aluminium capsule for packed bed domestic heat storage systems

Investigation of In–48Sn as a phase change material candidate for thermal storage applications

Latent heat storage systems provide large thermal storage densities for solar energy storage for various domestic and industrial applications. In–48Sn, an alloy of indium and tin a lead-free solder is investigated as a phase change material (PCM) in latent heat storage systems for heating applications. Results obtained from differential scanning calorimetry indicate that the alloy is useful in storing sensible heat beyond its melting temperature as it exhibits very little decomposition up to 400 °C. Though In–48Sn possesses a low latent heat of fusion, its high density allows for a larger thermal storage mass. The behaviour of In–48Sn in a 50 mm aluminium spherical capsule during charging and discharging cycles is investigated using sunflower oil as the heat transfer fluid (HTF) at flow rates of 3, 6, 9 and 12 ml/s. The influence of the charging temperature on the charging characteristics of the encapsulated PCM is also investigated. The average charging and discharging rates of the encapsulated PCM show an increase with an increase in the HTF flow rate. The HTF temperature determines the maximum temperature attained by the PCM and thus the total energy stored by the encapsulated PCM. In–48Sn shows good potential as a PCM in a spherical aluminium capsule for packed bed domestic heat storage systems

Experimental Energetic and Exergetic Performance of a Combined Solar Cooking and Thermal Energy Storage System

Most solar cookers usually perform a single task of solely cooking food during sunshine hours. Solar cookers coupled with thermal energy storage (TES) material for off-sunshine cooking are usually expensive and require complex engineering designs, and cannot be used for dual purposes, for example, solar water heating and cooking. In this paper, a solar cooker that can perform dual tasks of cooking as well as storing thermal energy to be used during off-sunshine periods is presented. The experimental setup is composed of a parabolic dish, a solar receiver coupled with a flat plate and an oil-circulating copper coil for charging and discharging a storage tank. The objective of the experiment is to evaluate the energy and exergy thermal performance parameters of the dual-purpose system during charging and discharging cycles. The effect of the flow rate and the mass of the load are investigated while using sunflower oil as both the heat transfer fluid and the storage material. Charging and discharging experiments are conducted using four different flow rates (2, 3, 4, 5 mL/s), and with different masses (0.5, 1, 1.5, 2.0 kg) with water and sunflower oil as the test loads. The charging results show that the average energy and exergy rates as well as their corresponding efficiencies increase with an increase in the charging flow rate. On the other hand, the increase in the mass load tends to decrease marginally the average charging energy and exergy rates for water, and their corresponding efficiencies. For sunflower oil, the average charging energy and exergy rates and efficiencies showed a more pronounced decrease with an increase in the mass. Water generally shows higher charging and discharging energy and exergy efficiencies compared to sunflower oil with an increase in the flow rate. For discharging results, the correlations between the energy and exergy thermal performance parameters with respect to the flow rate and the heating load are not well defined possibly due to different initial storage tank temperatures at the onset of discharging and the inefficient discharging process which needs to be optimized in future

Experimental Energetic and Exergetic Performance of a Combined Solar Cooking and Thermal Energy Storage System

Most solar cookers usually perform a single task of solely cooking food during sunshine hours. Solar cookers coupled with thermal energy storage (TES) material for off-sunshine cooking are usually expensive and require complex engineering designs, and cannot be used for dual purposes, for example, solar water heating and cooking. In this paper, a solar cooker that can perform dual tasks of cooking as well as storing thermal energy to be used during off-sunshine periods is presented. The experimental setup is composed of a parabolic dish, a solar receiver coupled with a flat plate and an oil-circulating copper coil for charging and discharging a storage tank. The objective of the experiment is to evaluate the energy and exergy thermal performance parameters of the dual-purpose system during charging and discharging cycles. The effect of the flow rate and the mass of the load are investigated while using sunflower oil as both the heat transfer fluid and the storage material. Charging and discharging experiments are conducted using four different flow rates (2, 3, 4, 5 mL/s), and with different masses (0.5, 1, 1.5, 2.0 kg) with water and sunflower oil as the test loads. The charging results show that the average energy and exergy rates as well as their corresponding efficiencies increase with an increase in the charging flow rate. On the other hand, the increase in the mass load tends to decrease marginally the average charging energy and exergy rates for water, and their corresponding efficiencies. For sunflower oil, the average charging energy and exergy rates and efficiencies showed a more pronounced decrease with an increase in the mass. Water generally shows higher charging and discharging energy and exergy efficiencies compared to sunflower oil with an increase in the flow rate. For discharging results, the correlations between the energy and exergy thermal performance parameters with respect to the flow rate and the heating load are not well defined possibly due to different initial storage tank temperatures at the onset of discharging and the inefficient discharging process which needs to be optimized in future

Thermal Stratification Performance of a Packed Bed Latent Heat Storage System during Charging

Experimental thermal stratification evaluation of a packed bed latent heat storage is done during charging cycles. The packed bed latent heat storage system consists of adipic acid encapsulated in aluminum spheres. Sunflower oil is used as the heat transfer fluid during charging cycles. Stratification number profiles are used to evaluate thermal stratification in the storage system. Charging experiments are carried out with three different flow-rates (4 ml/s, 8 ml/s and 12 ml/s). Charging experiments are also done using the same flow-rate (8 ml/s) with three different set heater temperatures (220 °C, 240 °C and 260 °C). The lowest charging flow-rate (4 ml/s) shows the best variation of the stratification number profile since it shows the least drop from the peak value and the shortest charging interval. Different set heater temperatures show almost identical stratification number profiles. The effect of the charging flow-rate is more significant than the effect of the charging set heater temperature when evaluating thermal stratification for this particular system

Thermal Stratification Performance of a Packed Bed Latent Heat Storage System during Charging

Experimental thermal stratification evaluation of a packed bed latent heat storage is done during charging cycles. The packed bed latent heat storage system consists of adipic acid encapsulated in aluminum spheres. Sunflower oil is used as the heat transfer fluid during charging cycles. Stratification number profiles are used to evaluate thermal stratification in the storage system. Charging experiments are carried out with three different flow-rates (4 ml/s, 8 ml/s and 12 ml/s). Charging experiments are also done using the same flow-rate (8 ml/s) with three different set heater temperatures (220 °C, 240 °C and 260 °C). The lowest charging flow-rate (4 ml/s) shows the best variation of the stratification number profile since it shows the least drop from the peak value and the shortest charging interval. Different set heater temperatures show almost identical stratification number profiles. The effect of the charging flow-rate is more significant than the effect of the charging set heater temperature when evaluating thermal stratification for this particular system

Investigation of Heat Transfer Fluids Using a Solar Concentrator for Medium Temperature Storage Receiver Systems and Applications

Solar concentrator collectors have the potential of meeting the medium- and high-temperature thermal energy demands of the world. A heat transfer fluid (HTF) is a vital component of a concentrating system to transfer and store thermal energy. This paper presents the design development of a solar paraboloidal dish concentrator (SPDC) and a study of selected HTFs using the storage receiver system of the concentrator. The locally designed SPDC (diameter 1.21 m and height 0.20 m) has features like light weight, effortless tracking, convenient transportation along with high optical and thermal performance. Three HTFs, silicone oil (SO), engine oil (EO) and ethylene glycol (EG), are selected based on their favorable properties for medium temperature (150–300 °C) applications. The characteristic parameters of HTFs, heating rate (Rh), instant thermal efficiency (ηith) and the overall heat loss coefficient (UL), are illustrated and determined experimentally. A new characteristic parameter, the normalized maximum fluid temperature (Tnf), is also introduced in the paper. In the heating test, the maximum attained temperatures by fluids, SO, EO and EG are found to be 240 °C, 180 °C and 160 °C, respectively. The thermal efficiencies of SO, EO and EG are determined to be 45, 36 and 31%, respectively. The heating rate of 6.56 °C/s is found to be the maximum for SO. Through the cooling test, the overall heat loss coefficient (UL) is computed to be 14 W/mK, which is the least among the three fluids compared. The high thermal performance, environmental safety and chemical stability of silicone oil make it suitable for use in concentrators for medium-temperature heat transfer and storage applications