Energy Conversion and Management

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1 Energy Conversion and Management 52 (2011) Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: Design, construction and operation of spherical solar cooker with automatic sun tracking system Riyad Abu-Malouh, Salah Abdallah, Iyad M. Muslih Department of Mechanical and Industrial Engineering, Applied Science University, Amman 11931, Jordan article info abstract Article history: Received 15 March 2009 Received in revised form 2 December 2009 Accepted 21 July 2010 Available online 6 September 2010 Keywords: Solar cooking Sun tracking PLC control Frequency control In this work, the effect of two axes tracking on a solar cooking system was studied. A dish was built to concentrate solar radiation on a pan that is fixed at the focus of the dish. The dish tracks the sun using a two axes sun tracking system. This system was built and tested. Experimental results obtained show that the temperature inside the pan reached more than 93 C in a day where the maximum ambient temperature was 32 C. This temperature is suitable for cooking purposes and this was achieved by using the two axes sun tracking system. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The energy section in Jordan depends heavily on the imported oil and gas products. This energy policy put the country in tough economic situations and slowed down the economical growth in the last years. This situation is worsening by the dramatic increase in the crude oil prices worldwide and in the increased demand on energy consumption. Jordan lies in high solar insolation band, where the average insolation intensity on horizontal surface is approximately 5 7 kw h/m 2 /day, which is one of the highest in the world [1]. Biermann et al. [2] conducted a 1 year comparative field test of different types of cooking appliances including seven brands of solar cookers. The test took place in three study areas in South Africa and involved 66 families, who expressed their preferences for certain cooker types. Solar and wood (stoves and open fires) cookers were the most used cooking appliances. The families used solar cookers for about 38% of overall test days and for 35% of overall cooked meals and used wood cooking appliances for 42% of overall test days. Fuel consumption measurements showed overall fuel savings of 38% resulting in estimated payback periods (through monetary fuel savings) from 8 months onwards, depending on the cooker type and region. Solar cooking in boarding schools and communal centers in isolated areas demands heating of large quantities of food. Franco Corresponding author. Tel.: ** Corresponding author. addresses: mallouh@maktoob.com (R. Abu-Malouh), Salahabdalah_1964@ hotmail.com (S. Abdallah). et al. [3] presented three different kinds of absorbers, optimized to fulfill different functions in a concentrator of an area of 2 m 2. These alternatives allowed the possibility of satisfying the needs of a communal dining center, cooking for up to 30 children, once each concentrator has been installed. The policy formulation for substituting cooking energy by renewable energy is addressed in multi-criteria context. In this regard, a survey was conducted to evaluate the perceptions of different decision making groups on present dissemination of various cooking energy alternatives in India [4,5]. Nine cooking energy alternatives were evaluated based on 30 different criteria, among which were technical, economic, environmental, social, behavioral and commercial issues. It was found that liquefied petroleum gas stove is the most preferred device, followed by kerosene stove, box type solar cooker (BSC) and parabolic solar cooker (PSC). PSC were investigated by many researchers. Ozturk [6] constructed and designed a low cost PSC and experimentally evaluated its energy and exergy efficiencies. The energy output of the PSC varied between 20.9 and 78.1 W, whereas its exergy output was in the range of W. It was found that the energy and exergy efficiencies of the PSC were in the range of and respectively. Petela [7] analyzed a PSC of cylindrical trough shape from exergy point of view. Equations for heat transfer between three surfaces: (i) cooking pot, (ii) reflector, and (iii) imagined surface making up the system were derived. The exergy efficiency of the PSC was found to be relatively very low (equals approximately 1%), and about 10 times smaller than the respective energy efficiency which was in agreement with experimental data. Sonune and Philip [8] designed a Fresnel type domestic concentrating cooker, which has an aperture area of 1.5 m 2 and a focal length of /$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi: /j.enconman

2 616 R. Abu-Malouh et al. / Energy Conversion and Management 52 (2011) m and was found to provide an adequate temperature needed for cooking, frying and preparation of chapattis and capable of cooking food for a family of 4 5 persons. The BSC has also been a subject of investigations conducted by many researchers. El-Sebaii and Aboul-Enein [9] presented a transient mathematical model for a BSC with one step outer reflector hinged at the top of the cooker. The model was validated by comparing the temperature distribution obtained by computer simulation with experimental results. Good agreement between experimental and theoretical results was observed. The performance of a BSC with auxiliary heating was studied and analyzed with the aid of (i) a built-in heating coil inside the cooker and (ii) a retrofit electric bulb in a black painted cylinder [10]. The results showed that with the use of auxiliary energy, when necessary, a solar cooker may be used throughout the year in areas where electricity is available. The study also recommended (i) to place electric heating elements below the absorber tray in solar cookers which are to be built and (ii) to place a retrofit electric bulb for heating on the absorber tray for year-round cooking for cookers which have been already built. El-Sebaii [11] presented a simple mathematical model for a BSC with outer inner reflectors based on analytical solution of the energy-balance equations for different elements of the cooker. The cooker performance was investigated by computer simulation in terms of the cooker efficiency as well as characteristic and specific boiling times. Numerical calculations were carried out for different tilt angles of the outer reflector on a typical winter day in Tanta/Egypt. It was shown that at the optimum tilt angle of the outer reflector, which equals 60 C, the specific and characteristic boiling times are decreased by 50% and 35%, respectively, compared to the case without the outer reflector. The overall utilization efficiency of the cooker was found to be 31%. A hot BSC was designed, manufactured and tested in Istanbul Technical University [12]. In the theoretical analysis, the differential equations have been solved numerically by the fourth-order Runge Kutta method. The obtained theoretical results were compared with the experimental ones and showed a good match. A model to predict 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 (solar insolation, temperature difference and load distribution) was presented [13]. The model was validated for commercially available solar cookers of both the box and concentrating types. The model basis was a fundamental energy-balance equation. Coefficients for each term in the model were determined by regression analysis of experimental data. The valid range of model application included most of the feasible design space for family-sized solar cookers. The model was found to be applicable for estimating the cooking capacity of existing box type and concentrating type solar cookers and for determining the combinations of intercept area and heat loss coefficient required to cook a given quantity of food in a given climate. A simple wooden, hot box, with one reflector solar cooker was designed and several demonstration units were fabricated by El-Ghetany and Abdel Dayem [14]. The units were field tested and showed acceptable performance. Maximum inner temperature of the units reached 160 C under field conditions of Giza, Egypt (30 N). Different foods were cooked successfully such as rice, meat, fish, and beans. The time of cooking ranged from 1 to 2.5 h. A series of tests were carried out during nine days to compare the Sudanese BSC with some similar Indian designs [15]. Sudanese BSC showed better thermal performance. Using internal, external reflectors and sloping of the top cover enhanced significantly the thermal performance. This was revealed by the amount of heat absorbed and hence the achieved plate temperature. Algifri and Al-Towaie [16] outlined a method to determine a reflector s performance and its orientation factors that depend upon the elevation angle of the sun, the solar surface azimuth angle and the reflector tilt angle. The analysis was applied to a cooker placed in the city of Aden in Yemen. The results indicated with proper cooker orientation improvement in the performance of the cooker due to the reflector. It reached during the winter season more than 100% at lower elevation angles and more than 60% at high elevation angles. Factors governing the operation of three BSC models (HS7534, HS7033 and HS5521) were described [17]. The results showed that HS552I is cheaper, and its volume is only 35% compared to HS7033. Comparing the performance of HS7033 and HS5521 was also performed based on the data collected during testing with and without load. The results showed that the HS5521 has the same heat collection rate and is able to cook as fast as HS7033. Ekechukwu and Ugwuoke [18] presented the design philosophy, construction and measured performance of a plane reflector augmented BSC. The experimental solar cooker consisted of aluminum plate absorber painted with black matt and a double glazed lid. Predicted water boiling time using the two figures of merit compared favorably with the measured values. The performance of the cooker with the plane reflector was improved tremendously compared to the cooker performance without the reflector. A hot BSC with used engine oil as a storage material was designed, fabricated and tested to enable cooking even in the late evening [19]. The performance and testing of the cooker was investigated by measuring the stagnation temperatures and conducting cooking trials. The efficiency of the hot box storage solar cooker was found to be 27.5%. Kumar investigated the top heat losses, constituting the major losses in the BSC and affecting its thermal performance [20]. The investigation revealed that the pot water required less time to reach a certain temperature with an increase in solar radiation level while, as expected, it took longer time with higher values of load of water in the pots. Reddy and Rao [21] showed that the performance of conventional BSC can be improved by better designs of cooking vessels with proper understanding of the heat flow to the material to be cooked. An attempt was made to arrive at a mathematical model to understand the heat flow process to the cooking vessel and thereby to the food to be cooked. The mathematical model considered a double glazed hot BSC loaded with two different types of vessels, kept either on the floor of the cooker or on lugs. It was found experimentally and by modeling that the cooking vessel with a central cylindrical cavity lugs results in higher temperature of the thermal fluid than that of a conventional vessel on the floor or on lugs. El-Sebaii and Ibrahim constructed and tested a BSC with one or four cooking pots under the weather conditions of Tanta city in Egypt [22]. Experiments were performed during July 2002 using the cooker with and without load. The cooker was able to cook most food kinds with an overall utilization efficiency of 26.7%. Amer introduced a novel design of solar cooker, in which the absorber is exposed to solar radiation from top and bottom sides [23]. A set of plane diffuse reflectors were used to direct the radiation onto lower side of the absorber plate. The performance of the new cooker and the conventional BSC was investigated under same operating conditions. The obtained results show that the absorbers of the BSC and the double exposure cooker attain 140 C and 165 C respectively. Sharma et al. investigated the thermal performance of a prototype solar cooker based on an evacuated tube solar collector with phase change material (PCM) storage unit with commercial grade erythritol as a latent heat storage material [24]. Solar energy was stored in the PCM storage unit during sunshine hours and was utilized for cooking in late evening/night time. Noon and evening cooking experiments were conducted with different loads and

3 R. Abu-Malouh et al. / Energy Conversion and Management 52 (2011) loading times. Cooking experiments and PCM storage processes were carried out simultaneously. The system was found capable to cook successfully twice (noon and evening) in a single day during Japanese summer months. Noon cooking did not affect evening cooking, and the evening cooking using the PCM heat storage was found to be faster than noon cooking. It was noticed that the PCM did not melt in January (winter) in Japan. In summer, PCM temperatures reached more than 110 C at the time of evening cooking. Hence, erythritol was found to be a promising PCM for solar cooking. Sharaf [25] revealed the concept of conical focus and explained the design of a solar cooker on its basis. The conical cooker was practically tested for grilling both white and red meat in a record time and a method for obtaining real boiling temperature of water (100 C) using a solar heater was reported. The results showed that the conical cooker has advantages regarding ease of manufacture, low price, lightweight and efficiency. It also demonstrated its ability and suitability for cooking different kinds of meat and legumes. Narasimha Rao and Subramanyam investigated the role of the vessel inside the solar cooker [26]. It was found that raising the vessel by providing few lugs made the bottom of the vessel a heat transfer surface. This change improved the system s performance by improving the heat transfer rates in both heating and cooling modes. Despite their ability to provide adequate temperatures needed for cooking, frying and preparation of chapattis, all the aforementioned types of concentrating solar cookers, suffer like all concentrating solar cookers with manual tracking from their low efficiency. This low efficiency is due to the fact that the solar rays are not perpendicular to the cookers surface most of the day. Accordingly, it is expected that the efficiency can be considerably improved by keeping the solar rays perpendicular to the cookers surface by using an automatic sun tracking system [8,27] with the solar cooker. In this context, this paper presents the design, construction and operation of a solar cooker with automatic two axes sun tracking programmable logic controller (PLC) system, characterized by a fairly simple electromechanical setup which reduces cost, maintenance and the possibility of failure. 2. The automatic sun tracking system design and control The amount of power produced by solar system depends on the amount of sunlight to which it is exposed. As the sun s position changes throughout the day, the solar system must be adjusted so that it is always aimed precisely at the sun and, as a result, produces the maximum possible power. Single axis tracking systems are considerably cheaper and easier to construct, but their efficiency is lower than that of two axes sun tracking systems. On the other hand, some solar systems require only two axes tracking, such as point focus concentrators. Two axes sun tracking systems can be applied in all types of solar systems to increase their efficiency. A large number of investigations have been performed to design and employ two axes sun tracking systems, however, only a few were cited in the literature that investigated the effect of using two axes sun tracking systems controlled by a modern computerized control system, such as a programmable logic controller (PLC) control system. Barakat et al. [28] designed a two axes sun tracking system with closed loop system and with complicated typical electronic control circuits. They found that the energy available to the two axes tracker is higher by 20%. Neville [29] presented a theoretical comparative study between the energy available to a two axes tracker, an east west tracker and a fixed surface. It was found that the energy available to the ideal tracker is higher by 5 10% and 50% than the east west tracker and the fixed surface, respectively. Khalifa [30] performed an experimental study to investigate the effect of using a two axes sun tracking system on the thermal performance of compound parabolic concentrators (CPC). The tracking CPC collector showed a better performance with an increase in the collected energy of up to 75% compared with an identical fixed collector. Hession and Bonwick [31] introduced a sun tracking system for use with various collectors or platforms. The system used both analog and digital techniques with sun sensing phototransistors that enabled the sun s position to be resolved to a precision of better than 0.1. Baltas et al. [32] made a comparative study between continuous and stepwise tracking. They showed that unlike concentrating systems, flat plate photovoltaic (FPPV) arrays yielded almost the same energy when tracking in a stepwise fashion. Tracking motors could be idle for 1 or 2 h and yet obtain more than 98% of the energy obtained from a continuous tracking array. Brunotte et al. [33] presented a prototype two stage photovoltaic concentrator with concentration ratios up to 300 with one axis tracking. Such concentrators are very promising in reducing the cost of solar electricity conversion. In this work, the design of two axes tracking system was performed using an open loop control that is based on programmable logic controllers (PLC). The block diagram of the hardware components of the solar cooker with two axes sun tracking system is shown in Fig. 1. The PLC has a programmable memory in which the instructions are stored to implement the various functions that are used to control the tracking motors into the calculated positions. The electromechanical system shown in Fig. 1 was designed to drive the spherical solar cooker by means of two motors, one for tracking the sun around the vertical axis which is 220 VAC and another 24 VDC motor for east west tracking. A bridge rectifier supplied the 24 VDC motor with the required voltage. A frequency inverter provided the 220 VAC motor with the desired controlled voltage and frequency. A screw gear is used to reduce the speed of the 24 VDC motor and to transfer the rotational motion of the motor into translational one which is suitable to drive the spherical cooker in the up and down directions. A spur gear is used to reduce the speed of the 220 VAC motor and amplify the torque of the motor to drive the spherical cooker around the vertical axis. Spherical solar cooker tracks the sun by moving in prescribed way to maximize the incident radiation beam. 3. The governing equations The surface position is defined by two angles, b and c as shown in [34]. b is the slope of the surface and c is the surface azimuth angle. The calculated angles b and c (as a function of time) should be b input γ input PLC controller Bridge rectifier Frequency inverter 24VDC motor 220VAC motor Screw gear Spur gear Spherical solr cooker Fig. 1. Block diagram of the spherical solar cooker with two axes sun tracking system.

4 618 R. Abu-Malouh et al. / Energy Conversion and Management 52 (2011) inserted into the PLC system as a program [35]. The PLC system will control the work of the actuator so that it will track the positions of the sun. This programming method of the control function of real time is used in this work. It works efficiently in all weather conditions regardless of the presence of heavy dusty or cloudy conditions. To implement this method for two axes tracking, the surface positions are determined as follows: b ¼ h z ð1þ c ¼ c s where h z is the zenith angle of the sun and c s is the solar azimuth angle. The model that is used to calculate h z and c s values for Amman (latitude angle of / =32 ) is given as: d ¼ 23:45 sin þ n ð3þ 365 where d is the declination angle and n is the number of the day in the year. And cos h z ¼ cos / cos d cos x þ sin / sin d where x is the hour angle. And cos x ew ¼ tan d tan / where x ew is the east west hour angle. c s ¼ C 1 C 2 c 0 s þ C 1 C 1 C where tan c 0 s ¼ sin x sin d cos x cos / tan d C 1 ¼ 1 if jxj 6 x ew 1 if jxj > x ew 1 if ð/ dþ P 0 C 2 ¼ 1 if ð/ dþ < 0 C 3 ¼ 1 ifx P 0 1 ifx < 0 ð2þ ð4þ ð5þ ð6þ ð7þ ð8þ ð9þ ð10þ 4. Mechanical design of the solar cooker The spherical solar cocker is a device that is used to collect the sun light by using a set of concentrating mirrors. The system was designed using simple electromechanical setup to reduce cost, maintenance and possibility of failure. This system can also be easily installed and assembled. It is composed of a cocking pan fixed at the focus of a spherical dish. This dish collects the solar energy incident on it and concentrates it using 256 concentrating mirrors. These mirrors are fixed in place using silicon glue. The dimension of each mirror is of 6 by 6 cm. This dish is designed to track the sun by moving in a prescribed manner to minimize the angle of incidence of the radiation beam on its surface. This was achieved using a two axes tracking system. This system is composed of the two motors shown in Fig. 2. One of them rotates the dish around the horizontal axes. This motion results in a rotation in the y z plane (up and down motion). The other motor rotates the dish around the vertical axes. This motion results in a rotation in the x z plane (left and right). The combination of these two motions results in a precise tracking of the incident radiation beam. The rotation of the two motors is controlled by the two axes sun tracking system with PLC control designed before. This system actuates the two motors to rotate the dish in the desired direction that guarantees achievement of our goal desired from this design, which is to track the incident solar beams. All hardware components are located in the same control box, except the motors and their gears. Furthermore, in order to conserve the solar energy, plastic bags are used to cover the reflecting mirrors and the receptacle creating a green house effect and keeping the heat trapped. 5. Experimentation and results The spherical solar cooker with two axes sun tracking system was manufactured according to the desired design in the workshops at Applied Science University, in Amman Jordan. Photographs of this system are shown in Fig. 3. Experiments were done on the spherical solar cooker in the renewable energy laboratory on three days; 13/5/2008, 4/6/2008 and 12/8/2008. The measuring electronic parts were tested and calibrated before being used on the various tests. The global solar radiation on a horizontal surface was measured using Kipp and Zonen pyranometer with a sensitivity of lv/w/m 2. Two different calibrated thermocouples (type-k) coupled to digital thermometer Fig. 2. Parts of the mechanical design of the solar cooker.

5 R. Abu-Malouh et al. / Energy Conversion and Management 52 (2011) (a) (b) (c) Fig. 3. Photographs showing: (a) the whole system, (b) the pan and the dish, and (c) the control components. with a range of C were used to measure the temperature inside pan and outside pan. The thermocouples were of Testo 110 type with an accuracy of 0.2 C for a temperature range of ( 25 to +75 C). The experiments started from 8:30 morning to 4:30 afternoon. Figs. 4 and 5 show the variation in ambient temperature and the variation in the solar intensity through three summer days. Figs. 6 and 7 show the variation in temperature inside pan as a function of time and the variation of the outside pan temperature as a function of time. The figures show an increase in the temperature inside the pan during early hours of the day until it reaches Temperature Inside Pan ( o C) Ambient Temperature ( o C) Fig. 4. Ambient temperature variation as a function of time. Temperature Outside Pan ( o C) Fig. 6. Inside pan temperature variation as a function of time Solar Intensity (W/m 2 ) Fig. 5. The solar intensity variation as a function of time. Fig. 7. Outside pan temperature variation as a function of time. the maximum values around noon correspondingly to the highest solar radiation and then decreases due sunset. From the curve of temperature inside pan variation as a function of time it is seen that the temperature inside the pan reached 93 C in a normal summer day, where the maximum ambient temperature registered 32 C. This shows that the temperature inside the pan could still reach further higher rates on hotter days. It is noticed after studying all the curves, that the temperature inside the pan increases when the ambient temperature is hotter or where the solar intensity is prevalent. When using this system

6 620 R. Abu-Malouh et al. / Energy Conversion and Management 52 (2011) for cooking or simply heating water, the latitude of location, season, and wind speed and weather conditions as cloudy days or dusty days should be considered. It should be remembered that food containing moisture cannot get much hotter than 100 C in any case, so it is not necessary to cook at the high temperatures as indicated in standard cookbooks. Because the food does not reach too high temperature, it can be safely left in the cooker all day without burning. This type of cookers can be used to warm food, drinks and can also be used to pasteurize water or milk. On the other hand, from Fig. 4, it can be seen that the ambient temperature increases from the morning till noon, after that, it decreases gradually till sunset. This same phenomena can also be seen for solar intensity in Fig. 5, temperature inside pan in Fig. 6 and temperature outside pan in Fig. 7. It can also be seen from Fig. 4 that the ambient temperature at any given time in 13/5 is less than that for the same time in 4/6 and they both are less than that in 12/6. This is expected because 13/5 is at the end of spring season while 4/6 is at the beginning of summer and 12/6 is expected to be hotter than 13/5 and 4/6. This same phenomena can also be seen for solar intensity in Fig. 5, temperature inside pan in Fig. 6 and temperature outside pan in Fig. 7. Finally comparing the maximum ambient temperature (32 C) with the maximum achieved temperature inside the pan (93 C), it can be seen that the temperature inside the pan is considerably greater than the ambient temperature. This was achieved due to the solar beam concentrating system combined with the two axes automatic sun tracking system. The results of using parabolic solar cooker with automatic tracking [36] showed that the water temperature inside the cooker s tube reached 90 C in a typical summer day, when the maximum registered ambient temperature was 36 C. 6. Conclusion A spherical solar cooker was designed and constructed. A two axes sun tracking system was designed and constructed to control the spherical solar cooker rotation. This sun tracking system depends on PLC and frequency control. It assures that the sun light beam is normal to the dish at any time of the day. This results in the highest possible efficiency that can be achieved for the solar cooker. The new system was constructed and tested for three different days. By comparing the results of the spherical solar cooker in this study compared with the results of the parabolic solar cooker with automatic sun tracking system in [36], the simple comparison shows that; the spherical solar cooker provided higher power than the parabolic solar cooker. Where, the water temperature inside the cooker s tube reached 90 C in typical summer days when the maximum registered ambient temperature was 36 C. While for the system in this study, results show that a temperature as high as 93 C or higher can be achieved. This temperature is sufficient and safe for cooking purposes especially for sites that are far from any city. References [1] Badran O. Study in industrial applications of solar energy and the range of its utilization in Jordan. Renew Energy 2001;24: [2] Biermann E, Grupp M, Palmer R. Solar cooker acceptance in South Africa: results of a comparative field test. Energy 1999;66: [3] Franco J, Cadena C, Saravia L. Multiple use communal solar cookers. Sol Energy 2004;77: [4] Pohekar S, Ramachandran M. Multi-criteria evaluation of cooking energy alternatives for promoting parabolic solar cooker in India. Renew Energy 2004;22: [5] Pohekar S, Ramacharidran M. 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