Design, Construction, and Evaluation of the Performance of Dual-Axis Sun Trucker Parabolic Solar Cooker and Comparison of Cooker

Department of Environmental Engineering, College of Biological and Chemical Engineering, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia Sustanable Energy Center of Excellence, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia Bioprocess and Biotechnology Center of Excellence, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia Environmental Protection and Green Development Commission, Addis Ababa, Ethiopia


Introduction
Energy is one of the necessities to live on this planet [1,2]. Plants use energy to prepare their food, humans use energy to cook their food, and industries use energy to manufacture different products [3]. In early times, energy is completely harnessed from fossil fuels (coal, oil, and natural gas). As humans become more civilized, their industries also grow, which in turn increased energy demand. e rapid increment in population also contributed to the increment of energy demand [4][5][6].
is caused an increment in the utilization of fossil fuels. Eventually, this started to degrade the environmental quality [7]. Global warming, which is caused by the increase in the concentration of greenhouse gases in the atmosphere due to the burning of fossil fuels, causes the increment of the earth's mean temperature [8,9].
is in turn causes climate change, which is responsible for different hazards such as floods and drought [10]. e burning of fossil fuels also causes acid rain, which can cause an adverse impact on forests, freshwater, and soil [11]. e fluctuation and increment of fossil fuel prices were also the other problems that affected countries, whose economy depends on nonrenewable energy [12]. Moreover, according to Hafner and Tagliapietra [13], after a few hundred years, all fossil fuels in sub-Saharan African countries will be extracted.
To solve the above problem, in addition to energy conservation, researchers started to study more about alternative energy resources such as solar, wind, hydro, geothermal, tidal, and biomass, which are commonly called renewable energy [14][15][16][17]. ese energy sources are clean and environmentally friendly. Green energy (renewable energy) plays an important role to have affordable, accessible, and reliable energy for all [18]. Renewable energy diversifies the energy source and reduces the utilization of fossil fuels [19,20]. Unlike solar energy, most renewable energy sources require high technological advancement for installation and operation [21]. erefore, solar energy is a preferable energy source for developing countries including Ethiopia [22][23][24]. Solar energy has the potential to become the primary energy source in all Africa countries [25]. is is mainly due to the high solar intensity reaching the earth's surface [26]. Also, these countries get solar energy for a longer period throughout the year [27]. According to Griffiths [28], most of the continent enjoys sunshine for a longer season per year. Due to the spherical shape of the earth, the surface of the earth will not get uniform solar radiation [29]. Countries such as Ethiopia, which are located near the equator, can get a bigger advantage from this energy source because of the high solar intensity. According to Khadem et al. [30], the annual average daily radiation on a horizontal surface in Ethiopia is 3.74 kWh/m 2 with a minimum of 1.5 and a maximum of 4.9 kWh/m 2 . We can use solar energy for different purposes such as generating electricity, boiling water, and cooking food [31].
Nearly 730 million people in sub-Saharan Africa countries rely on biomass as a primary energy resource [32]. Among the different types of biomass, most African countries utilize firewood, which indicates that deforestation is a big problem in this continent [21]. In Ethiopian rural areas, firewood is the main source of energy, but in cities, electricity, kerosene, and charcoal are the main sources [33].
In Ethiopia, over 80% of the population utilizes biomass as a primary source of energy [34]. According to Overend [35], the main reason for the consumption of biomass in sub-Saharan countries is for cooking purposes. In most developing countries, there is a shortage of firewood due to the high consumption of energy and cooking in an inefficient stove in a poorly ventilated space [36]. Cooking food requires firewood gathering and frequent attention to make sure the food cooks evenly. Moreover, when women and children collect firewood for cooking and other purposes, they may face sexual harassment such as rape, unwanted pregnancy, psychological problem, and sexually transmitted diseases [37]. Utilizing charcoal in poorly ventilated spaces can cause a serious respiratory problem due to the emission of carbon monoxide and other gases [38]. Kerosene is expensive; therefore, it is not usually utilized in rural areas [39]. Electricity is cheap, but it has low coverage in rural areas of most developing countries [40].

Literature Review
A solar cooker is a device that uses the sun's energy to cook food [15,41]. Solar cookers can eliminate the problems that come with utilizing firewood, charcoal, kerosene, and electricity. Unlike firewood, charcoal, and kerosene, solar cookers do not emit harmful gases that can cause air pollution and global warming [31]. Fire accidents will not be a problem in cooking with solar cookers. No trees have to be cut for firewood, which in turn helps to prevent soil erosion [42]. Unlike kerosene, since they use only the sun's energy, they are not expensive. Unlike electricity, they can cover all parts of rural areas without spending a big budget. Box, parabolic, and panel cookers are the three main types of solar cookers [43]. Solar cookers use solar radiation either by reflecting the radiation to concentrate on a cooking pot or by retaining the radiation to trap the heat [44].
A parabolic solar cooker is one of the main solar cookers, which can cook food and boil water at a high temperature within a short period [2,45,46]. According to Mbodji and Hajji [47], parabolic solar cookers can be designed and manufactured for thermal applications. In a parabolic solar cooker, the reflecting material, which is shaped in a parabola, receives the sun radiation and reflects it to the bottom of the cooking pot. is causes the heating effect, which will be used to cook different foods [44,48,49]. A parabolic solar cooker requires a frequent adjustment of the cooker towards the sun [2].
Arenas experimented on a parabolic solar cooker and discovered that this cooker can achieve an average power scale of 175 W and an efficiency of 26.6% [50]. Al-Soud et al. designed and constructed a two-axis automatic sun trucker parabolic solar cooker and experimented in 2008 for three days. During the experiment, the water temperature had reached 90°C at an ambient temperature of 36°C [46]. Suple and ombre experimented on a parabolic solar disc that can be operated from the kitchen through biaxial manual tracking [51]. Lee and Rao constructed the three main types of solar cooker and discovered that the parabolic solar cooker achieved the highest temperature at 86.5°C. Moreover, different technologies regarding parabolic solar cookers are being developed throughout the world [52][53][54][55].
As far as the knowledge of the authors is concerned, only a few researches have been conducted regarding the performance of parabolic solar cookers in Ethiopia [55,56]. Moreover, in Ethiopia, a comparison of the parabolic solar cooker with other fuels in terms of cooking time and energy cost has not yet been investigated. erefore, this study aimed to design, construct, and evaluate the performance of parabolic solar cookers and compare the cooker with firewood, charcoal, kerosene, and electricity in terms of cooking time and energy cost of cooking.

Description of the Study Area.
e experiment was conducted in a site, which is located in Addis Ketema subcity, Addis Ababa, Ethiopia. e site is located at 90°0 2′59″ and 38°43′54″ and has an altitude of 2459 m. According to the data that is collected from the Ethiopian metrological agency, Addis Ketema has an average temperature, rainfall, and relative humidity of 15.9°C, 1089 mm, and 60.7%, respectively. Figure 1 shows a map of the study area.

Experimental Design and Operation of Parabolic Solar
Cooker. To construct a parabolic solar cooker, one old satellite dish with its base, four small tyers, steel (Ø � 25 mm), adhesive, aluminum foil, and a small pot were used. e old dish was first washed with tap water to remove the dirt and dried using a clean towel. en the surface of the dish was covered with aluminum foil with the help of adhesive. Four small tyers were welded on the stand base so that the cooker can track the sun from east to west. e stand base can also track the sun from north to south because of its capacity to stretch from 72 cm to 108 cm. is particular future makes the cooker have a dual-axis tracking capacity that can track the sun east to west daily and north to south seasonally. Figure 2 shows the different components of the cooker. e schematic diagram of the parabolic solar cooker is shown in Figure 3. e aperture area, receiver area, focal length, rim angle, arc length of the paraboloid, surface area of a paraboloid, length of the circumference, and concentration ratio of the parabolic solar cooker were designed based on the formulas that are listed in Table 1.
By using the calculated focal length, steel support was constructed and welded on the stand base. By considering the diameter of the pot, a receiver, which is used to suspend the pot and keep it on the focal point, was constructed and welded on the support steel. As shown in Figure 4, the bottom part (Ø � 16.00 cm) of the pot can pass through the ring-shaped receiver (Ø � 16.22 cm), but the upper part of the pot (Ø � 16.44 cm) could not pass through the ring. e pot was painted black because of the high absorption of light and the low reflective property of the color. e depth of the parabola (d) and circumference of the circle (C) were 0.3 m and 5.76 m, respectively. Finally, all components of the cooker were assembled as shown in Figure 5.

Performance Evaluation of the Cooker.
e generated data were analyzed by Microsoft Excel 2013. e performance of the cooker was evaluated using the following formulas: S � solar radaiation data number of data , where η denotes efficiency, Q input denotes heat energy input (kJ), Q output denotes heat energy output (kJ), m1 denotes the mass of water before boiling (g), m2 denotes the mass of water after water (g), Cp denotes specific heat capacity of water, ∆T denotes a change in temperature, L denotes latent heat of vaporization of water, A denotes aperture area of the paraboloid, S denotes average upcoming solar radiation, P denotes power, and h denotes the hour. Q output is determined by boiling one liter of water using a parabolic solar cooker for 36 minutes. e Cp and L of water are 4.186 J/g°c and 2260 kJ/kg, respectively. e metrological data was used to determine the upcoming solar radiation (S), which in turn helps to determine Q input. e solar radiation data was collected from the Ethiopian metrological stations. Table 2 shows the metrological data of the experimental site during boiling 1 L water. is data was collected from the Ethiopian metrological agency.where A denotes the energy cost of cooking/boiling for a family, B denotes the energy cost of cooking/boiling for a single person, C denotes the consumption of food for one family, which have five members, E denotes the amount of fuel used to cook foods and boil water, and F denotes the cost of fuel in kg for charcoal and firewood, litter for kerosene, and kW for electricity. Table 3 summarizes the amount of fuels used to cook different foods and boil water so that they could be compared with the constructed parabolic solar cooker in terms of cooking time and energy cost of cooking. Table 4 summarizes the quantity of foods that are cooked by the parabolic solar cooker and the cooking time interval. In cooking different foods and boiling water, the parabolic solar cooker was adjusted by rotating it from north to south and east to west so that a high amount of solar radiation can be received and reflected to the concentrator. e adjustment was conducted by considering the hour of the day and season. e same type and quantity of foods are cooked using charcoal, firewood, kerosene, and electricity for comparing the parabolic cooker with these fuels. In addition, for this study, the average consumption  Journal of Renewable Energy of a family, which has five members, was taken per some specified period. Table 5 summarizes the design results of the constructed parabolic solar cooker, which is designed based on the formulas listed in Table 1.

Performance of Parabolic Solar
Cooker. e output energy, average solar radiation, input energy, efficiency, and power of the cooker were calculated based on equations (1)- (5) and are presented in Table 6. e incoming solar radiation was concentrated on the focal point, which is located on the receiver, using the concentrator (parabolic dish). At a time of the day, which has high solar radiation, a high amount of solar radiation will be concentrated on the receiver, which leads to the presence  Aperture area (Aa) π(ra) 2 Equation (1)  2 Receiver area (Ar) π(rr) 2 Equation (2)  3 Focal length (F) (ra) 2 /4 h Equation (3)  4 Rim angle (Q) tan(Q) � (1/((d/8 h) − (2 h/d))) Equation (4)  5 e surface area of the paraboloid (As) Length of the circumference (L) π * Da Equation (6)  7 Concentration ratio (C) Aa/Ar Equation (7) 1.       Length of the circumference (L) 5.76 m 11

Journal of Renewable Energy
Concentration ratio (C) 123.46 of high temperature. e black-painted pot, which is placed on the receiver, will absorb the heat and be used to cook different foods and boil water. In this study, the efficiency of the constructed parabolic solar cooker was 10.75%. However, better efficiency of 37.75% and 26.6% was achieved by [57,58], respectively. Many factors could reduce the efficiency of the cooker. Some of the factors are temperature, wind, cloud, day of the year, time of the day, and type of reflective material. Profile deformation, structural torsion, and local irregularities can also affect the efficiency of a parabolic solar cooker [59]. e reflective material that is used in this cooker was aluminum foil. Aluminum foil is a good reflector, but after some time, it will crack. In addition, it will not be placed smoothly on the dish. is causes the rays not to concentrate on a receiver, which in turn reduce the efficiency of the cooker.

Comparison of Parabolic Solar Cooker with Other Fuels in terms of Cooking Time and Cost.
e constructed parabolic solar cooker was compared with charcoal, firewood, kerosene, and electricity in terms of cooking time and cost. Figure 6 shows the cooking time of different foods using the constructed parabolic solar cooker, charcoal, kerosene, firewood, and electricity.
To compare parabolic solar cookers with other fuels, water and different foods are used, whose composition is described in Table 4. In boiling water to 88°C, the parabolic solar cooker took twelve minutes, but charcoal, kerosene, electricity, and firewood took eleven, thirteen, sixteen, and ten minutes, respectively. Except for firewood, a parabolic solar cooker boiled the water faster than the other fuels. In cooking an egg, a parabolic solar cooker took sixty minutes, but charcoal, kerosene, electricity, and firewood took thirty, twenty-nine, twenty-eight, and twenty-six minutes, respectively. Firewood can cook an egg faster than both parabolic solar cookers and the other fuels. In cooking potato, parabolic solar cooker took hundred minutes, but charcoal, kerosene, electricity, and firewood took fortythree, thirteen, fourteen, and fifteen minutes, respectively. Kerosene can cook potatoes faster than both parabolic solar cookers and the other fuels.
In cooking Nefro, parabolic solar cooker took forty minutes, but charcoal, kerosene, electricity, and firewood took one hundred thirty-five, ninety, ninety-one, and sixty-three minutes, respectively. e parabolic solar cooker can cook Nefro faster than the other fuels. In cooking Shero wet, parabolic solar cooker took eighteen minutes, but charcoal, kerosene, electricity, and firewood took seventy-nine, sixtysix, sixty-eight, and sixty minutes, respectively. Except for firewood, a parabolic solar cooker can cook Shero wet faster than the other fuels. In cooking Siga wet, parabolic solar cooker took one hundred thirty minutes, but charcoal, kerosene, electricity, and firewood took seventy-nine, sixty-six, sixty-eight, and sixty minutes, respectively. Firewood can cook Siga wet faster than both parabolic solar cooker and the other fuels. In cooking rice, a parabolic solar cooker took forty-three minutes, but charcoal, kerosene, electricity, and firewood took thirty, thirty-three, twenty-five, and twentythree minutes, respectively. Firewood can cook potatoes faster than both parabolic solar cookers and the other fuels. Parabolic solar cooker cooks Nefro and Shero wet faster than any other fuels. e reason for this is the fact that these foods were cooked around noon. It is well known that there is a high amount of solar radiation at noon period. If there is a high amount of solar radiation, the cooking time will be small.
Generally, even though the parabolic solar cooker took a longer time to cook an egg, rice, potato, and Siga wet than the other fuels, it cooks Nefro faster than the other fuels. It is also the second-fastest cooker in cooking Shero wet compared to the other fuels. Nefro and Shero wet were cooked around solar noon, where the solar intensity becomes highest. Table 7 shows the energy cost of different fuels to boil oneliter water and to cook one egg, potato, Nefro, Shero wet, Siga wet, and rice. ese foods were also cooked by the parabolic solar cooker. e energy cost of these fuels is calculated by considering the amount of fuel used to cook the given foods with a unit cost of the fuel, which is described in Table 3.
As shown in Table 4, a family requires Shero wet 2 times per day, Nefro 4 times per day, 15 L water, 10 eggs, 10 potatoes, Siga wet 2 times per day, and rice 1 time per day . Figure 7 shows the energy cost of different fuels in boiling water and cooking different foods for a single family.

Conclusion
A dual-axis sun-tracking solar cooker was designed and constructed using locally available materials. e design parameters were aperture area, receiver area, focal length, rim angle, the surface area of the paraboloid, length of the circumference, and concentration ratio. Its performance was also investigated by calculating its efficiency and comparing it with charcoal, firewood, kerosene, and electricity in terms of cooking time and energy cost of cooking. e average solar radiation reaching the earth's surface on the day of the experiment was 0.665 kW/m 2 . e output energy, input energy, efficiency, and power of constructed parabolic solar cooker were 0.182 kW, 1.691 kW, 10.75%, and 0.3 kW/hr, respectively. e constructed parabolic solar cooker showed the best performance in cooking Nefro and Shero wet at a short time compared to the other fuels. e parabolic solar cooker showed a good performance in boiling water for a short time next to firewood and charcoal. However, the parabolic solar cooker took a relatively long time in cooking egg, potato, and Siga wet. One of the main reasons for the slow cooking time might be due to the cracking of the reflective material (aluminum foil), which is also responsible for the reduction of the efficiency of the cooker. Since the parabolic solar cooker does not have any energy cost, it can save the energy cost of cooking foods.

Recommendation
e reflective material that was used in this experiment was aluminum foil. is material cracks and shrinks after some time, which leads to the reduction of efficiency of the cooker. erefore, further investigation should be conducted to replace aluminum foil with a reflective material that is strong and durable to improve the efficiency of the cooker. Generally, due to its cost and time effectiveness, a parabolic solar cooker will be a very good technology especially for developing countries including Ethiopia.

Data Availability
All data are available within this article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.