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- Experimental thermal performance evaluation of different configurations of Copenhagen solar cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo Andres, Antonio; Ruivo, CelestinoIn this work, four different configurations of Copenhagen solar cookers were tested experimentally at the same time under the same weather conditions. First tests were carried out using pots without water load. Secondly, tests were performed with the equal amount of water in each pot. Thirdly, tests were carried out with different amounts of water for one of the configurations. From the results of the first set of tests, it was found that the performance of one of the configurations depends more significantly on the solar altitude angle than the others. A large number of experiments for each set of tests were conducted covering a wide range of solar altitude angles. A thermal performance analysis based on the ASAE S580.1 standard was performed with the measured data of the second and third sets of tests. The obtained plots with the observation points of each configuration evidence that the linear trend of the standardised power is not universal. The observed trends are very dependent on the solar altitude angle. Thus, the procedure for evaluating standardised power recommended by the standard for cooker performance comparison should be improved.
- Optical characterization of a funnel solar cooker with azimuthal sun tracking through ray-tracing simulationPublication . Carrillo-Andrés, Antonio; Apaolaza-Pagoaga, Xabier; Ruivo, Celestino; Rodríguez-García, Eduardo; Fernández-Hernández, FranciscoFunnel type solar cookers are simple and effective. Most of them rely on a multifaceted reflector to concentrate solar radiation on a cooking pot that is placed inside a transparent enclosure to create a greenhouse effect. The analysis of the resulting optical system is a complex task, as multiple reflections occur. The overall performance of funnel solar cookers is strongly affected by their optical efficiency. There is a lack of information in academic literature about this important research topic. This work aims to fill this gap presenting an optical performance analysis of a funnel solar cooker with only azimuthal sun tracking. Open-source numerical ray-tracing software Soltrace is used to investigate relevant characteristics such as the intercept factor, optical efficiency, dependency on incidence angle, performance of each reflecting surface and irradiation density flux distribution on different surfaces of the cooking pot. Some important results for beam radiation at normal incidence are the intercept factor, determined to be 0.664, and the optical efficiency with realistic optical properties, that turned out to be 0.370. When the incidence of solar beam radiation is not normal, optical efficiency remains above 90% of its normal incidence value, if the alignment errors are less than 10 degrees.
- On the use of experimental measured data to derive the linear regression usually adopted for determining the performance parameters of a solar cookerPublication . Ruivo, Celestino; Apaolaza-Pagoaga, Xabier; Di Nicola, Giovanni; Carrillo-Andrés, AntonioIn the present work, the results of testing panel and box solar cookers are used to investigate the suitability of using the linear regression for estimation of the performance parameters of a solar cooker. The panel cooker and the box cooker were experimentally tested with glycerine and peanut oil, respectively. An exponential fitting to the plot of measured load temperature versus time is used to derive the linear regression between the instantaneous efficiency and the specific difference of temperature. The linear regression curve is compared with the corresponding experimental curve. Minor deviations are observed in the case of the panel cooker, but only in the middle part of the test. In the case of the box cooker, the deviations are very significant during the whole test. The present work presents the simplified formu-lation associated with the physical problem. It points out the importance of performing further research to develop a more accurate procedure. The determination of parameters based on the linear regression cannot be seen as a universal procedure applicable to all types of cookers. The opto-thermal ratio and the maximum achievable load temperature are overestimated.
- Experimental characterization of the thermal performance of the Haines 2 solar cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Ruivo, CelestinoThis work presents the most exhaustive experimental characterization of the thermal performance of the Haines 2 solar cooker available to date. Two Haines 2 solar cookers were tested side-by-side in Malaga, Spain, 36.7 N, between May 2021 and December 2021. A novel test procedure using empty pots and a tilted plane with variable inclination gave useful information about the influence of the solar altitude angle on cooker performance, and allowed identification of the best range for each of the two available reflector configurations for this cooker. Some suggestions are given to improve the cooker design for low solar altitude angles. In addition, a large number of water heating tests partly based on the ASAE S580.1 standard protocol were conducted to i) determine the standardised power, ii) examine the influence of the solar altitude angle, and iii) investigate the impact of using partial loads. All these results provide a complete characterization of the performance of this cooker in a wide range of operating conditions of practical interest. It is recommended that future versions of ASAE S580.1 standard consider the influence of both solar altitude angle and partial loads.
- Proposal of a non-linear curve for reporting the performance of solar cookersPublication . Ruivo, Celestino; Apaolaza-Pagoaga, Xabier; Coccia, Gianluca; Carrillo-Andrés, AntonioPerformance parameters of solar cookers have conventionally been determined by assuming a linear trend between the cooker power and the difference between load temperature and ambient air temperature. This approach may not be convenient for some solar cooker designs. In the present work, the suitability of a non-linear regression derived from fitting the measured load temperature to a second order exponential polynomial was investigated and compared with the linear regression. Both regressions were compared with the corresponding experimental curves of a panel cooker and a box cooker. In the case of the panel cooker, the linear trend of the experimental plot was confirmed over a large period of the conducted test. Minor deviations from the experimental data were observed only at the beginning and at the end of the test. On the contrary, in the box solar cooker, significant deviations between the linear regression plot and the experimental points were observed, while smaller deviations were obtained using the non-linear regression. Thus, the proposed method can be seen as a promising approach that should be considered when updating the existing procedures for testing and reporting the performance of solar cookers.
- Concentrating solar cookers in urban areas: establishing usefulness through realistic intermediate temperature rating and gradingPublication . Sagade, Atul A.; Apaolaza-Pagoaga, Xabier; Ruivo, Celestino; Carrillo-Andrés, AntonioConcentrating Solar Cookers (CSCs) are well-known for fast cooking and can significantly contribute to attaining the United Nation's sustainable development goals. CSCs attain intermediate temperatures (120-240 degrees C) and are suitable for several cooking applications. The realistic rating and grading of CSCs is inevitable for establishing their usefulness in urban areas, which is the main objective of the present work. This paper reveals the experimental results of two existing concentrating solar cookers with different geometries and aperture areas. The first cooker is a shallow satellite antenna parabolic dish, and the other is a small deep parabola. Cooker Opto-thermal Ratio (COR) acts as a thermal performance parameter, and glycerin as a test load for their performance evaluation.The mean values of COR for the cookers, CSC1, and CSC3, are 0.180 and 0.092, respectively. The typical theoretical values of maximum achievable fluid temperature are 192.9 and 113.9 degrees C, respectively, and that for reference time are 23.8 and 60.5 min for CSC1 and CSC3, respectively. COR identifies the variation in the performance of CSCs based on a design change. The objective parameters enable realistic intra-cooker performance comparison of the CSCs at intermediate temperatures. The results depict that the existing designs of CSCs can be graded appropriately using COR and provide new insights into their performance at intermediate temperatures realistically. TPP-based realistic rating and grading of existing designs of solar cookers enable their effortless selection as per end-user requirements and help in the faster propagation of solar cooking technology in urban and semi-urban areas.
- Performance of solar funnel cookers using intermediate temperature test load under low sun elevationPublication . Apaolaza-Pagoaga, Xabier; Sagade, Atul A.; Ruivo, Celestino; Carrillo-Andrés, AntonioSolar funnel cookers can be designed as attractive and affordable low-cost devices accessible to people in all continents of the world regardless of their walk-in life. The present work is aimed to investigate the applicability of funnel cookers to attain the temperature in excess of the boiling point of water. It widens their acceptability for cooking and opens new opportunities for technological developments in such designs of solar cookers. Two identical designs of funnel cookers, FC1 and FC2, have been tested with appropriately sized identical cooking pots and glass enclosure to serve the purpose. Cooker FC2 is tested with a glass enclosure only, while a glass enclosure is not used in FC1. Glycerine is used as a test load. Cooker Opto-thermal Ratio (COR) as a thermal performance parameter and overall cooking efficiency are used to compare the performance of the two funnel cookers. It is shown that the temperature of the test load in the cooker FC2 can reach 140 to 150 degrees C. So, this funnel cooker design can be preferred for cooking food at a relatively high temperature over the boiling point of water. The experimental results show that: i) the mean values of the Cooker Opto-thermal Ratio for cookers FC2 and FC1 are estimated to be 0.157 and 0.110 (m2 degrees C)/W, respectively, and ii) the values of the overall cooking efficiency for cookers FC2 and FC1 are estimated to be 11.8% and 10.2%, respectively.
- Standardised power of solar cookers with a linear performance curve following the Hottel-Whillier-Bliss formulationPublication . Ruivo, Celestino; Coccia, Gianluca; Di Nicola, Giovanni; Carrillo-Andrés, Antonio; Apaolaza-Pagoaga, XabierIn the present work, an improvement of protocol widely used for reporting the thermal behaviour of solar cookers is communicated to the scientific community. The linear regression used to represent the standardised cooking power is based on the well-known Hottel-Whillier-Bliss equation written in dimensionless format. The authors’ new formulation procedure for estimating the standardised power includes a correction for the difference between the load temperature and the ambient air temperature of the procedure of ASAE S580.1 Standard. It is derived from a simple theoretical deduction, similar to the ones usually applied to solar thermal flat collectors. The correction factor relates itself with the ratio between the measured solar irradiance and the solar irradiance chosen as a standard value. As one example, test results of a funnel cooker loaded with water are used to show the impact of the improvement of the procedure for reporting performance of a solar cooker. The procedure is valid only for solar cookers evidencing a clear linear performance curve.
- The effect of partial loads on the performance of a funnel solar cookerPublication . Apaolaza-Pagoaga, Xabier; Carrillo-Andrés, Antonio; Ruivo, Celestino; Fernández-Hernández, FranciscoSeveral solar cooker designs have been proposed over the last decades. The funnel cooker is a well-known model, representative of the category of panel-type solar cookers. From the empirical experience of real practice, it is known that the use of partial loads has an impact on the performance of the cooker. However, this effect has not yet been investigated rigorously. This work aims to fill this lack. Extensive experimental work was performed to determine the effect of partial loads on a funnel cooker thermal performance. Tests were conducted on two identical funnel cookers, in Malaga, Spain, with low sun elevation. Cookers were tracked only azimuthally. Experimental protocol was based on ASAE 580.1 Standard for better replicability. Results showed that the standardised power drops by about 15% of the original value when the water volumetric load fraction drops by 25%, for both cooker operations, with and without glass enclosure. This important reduction is explained on how the fill level of the cooking vessel affects its function as a thermal radiation receiver. Results from experimental tests were correlated into a simple formula of practical interest. Finally, a new cooking vessel design, that improves performance at partial loads, i.e., a 25.4% increase in cooker power, was proposed and tested.
- Experimental determination of the standardised power of a solar funnel cooker for low sun elevationsPublication . Ruivo, Celestino; Carrillo-Andres, Antonio; Apaolaza-Pagoaga, XabierOver the past few decades, many efficient solar cooker designs have evolved. It is important to measure their performance and communicate this information to researchers, manufacturers and users around the world. Funnel type solar cookers are simple, effective and have multiple advantages in practical use, but there is limited experimental data about them in the academic literature. This work provides performance data for a well-known design of funnel cooker. When possible, the experimental protocol was based on the ASAE S580.1 Standard. The following procedures were added to improve the quality and reliability of the measured data: i) two identical funnel cookers were tested simultaneously, side by side, to control for weather variables, ii) a large number of observations were made iii) confidence and prediction intervals were calculated for the main figures of merit iv) cooled water was used to extend the range of valid observations. Tests were conducted in Malaga, Spain, at latitude 36.9 degrees N, between November 2019, and February 2020, a period with low sun elevation. Azimuthal solar tracking was applied. Two different pot lids were compared to investigate their influence on the standardised cooker power obtained. (C) 2021 Elsevier Ltd. All rights reserved.