
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)12895-2
10.1016/j.heliyon.2024.e36864
e36864
Research Article
Design of an injera baking system using parabolic trough solar collectors at Mekelle University cafeteria
Retta Habtamu Terefe habtamu555@gmail.com
a⁎
Hailu Mesele Hayelom mesele.hayelom@mu.edu.et
a
Baheta Aklilu Tesfamichael aklilu.tesfamichael@aastu.edu.et
b
Haile Misrak Girma misrak.girma@aastu.edu.et
b
a Mekelle University, Ethiopia
b Addis Ababa Science and Technology University, Ethiopia
⁎ Corresponding author. habtamu555@gmail.com
24 8 2024
15 9 2024
24 8 2024
10 17 e3686426 3 2024
20 8 2024
23 8 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
Injera baking poses a significant energy demand and strain on the national grid, requiring temperatures of 180–220 °C with traditional clay Mitads. This study aimed to design a solar thermal system to replace electrical baking energy at the Mekelle University student cafeteria. The system, designed for baking 11,000 Injera within a 6-h daily operation, comprises 92 Anodized aluminum plate Mitads heated by hot oil from an oil gallery, stored in a hot oil storage unit, and recharged via a parabolic trough solar collector. A heat exchanger and thermal storage system ensure efficient heat transfer and storage. Computational Fluid Dynamics (CFD) and Soltrace analyses were conducted to assess temperature distribution on the baking pan and oil gallery surfaces, as well as solar thermal heat flux. Results revealed a heating capacity of 2.11 kW per Mitad, meeting the required capacity, and a system energy consumption of 1216.5 MJ per hour, achieving a thermal efficiency of 57.4 %. Baking Injera at higher temperatures, enabled by a uniform temperature distribution, yielded uniformly textured Injera with an optimal number of eye bubbles and prevented sticking to the Mitad. Consequently, this design offers a viable alternative for the energy-intensive application at the Mekelle University student cafeteria, providing valuable insights for future solar thermal Injera baking system designers.

Keywords

Mitad
Oil storage
Parabolic trough collector
Heat exchanger
Solar thermal baking system
==== Body
pmcNomenclatures

Symbols Descriptions

φ Acceptance angle

Ta Ambienttempérature [K]

Wa Aperture width [m]

Aap Aperture area of concentrator collector [m2]

Ar Aperture area of Receiver [m2]

Sp Arc length parabolic trough curve [m]

md Average mass of dough expected for one Injera [kg]

mw Average mass of water [kg]

minjera Average mass of Injera baked [kg]

IB Average Incident beam daily solar radiation during the sunshine period [W/m2]

cp, dougℎ Average specific heat of dough [kJ⁄ (kg. K)]

Tp Baking plate top surface temperature [K]

B Baffle spacing [m]

L Characteristic length [m]

Ct Clearance between adjacent tube [m]

Qc Convective heat loss [kJ]

ℎc Convective heat transfer coefficient [W⁄ (m2. K)]

F Correction factor [unitless]

ρ Density [kg⁄m3]

Daeff Effective aperture diameter [m]

Qu Energy required for baking Injera or useful energy [kJ]

Qs Energy stored by baking plate [kJ]

f Focal length of parabolic trough [m]

CR Geometric concentration ratio [unitless]

Af Geometric factor [unitless]

IG Global solar radiation [W/m2]

Q˙abs Heat absorbed by the collector [kJ]

ℎvap Heat vaporization of water [kJ⁄kg]

ΔTlm Log mean temperature difference [K]

HP Latus rectum of parabola equal to aperture width [m]

Nt Number of tubes

Nu Nusselt number [unitless]

m˙oil Mass flow rate of hot oil [kg/s]

U Overall heat transfer coefficient [W⁄ (m2. K)]

ηo Optical efficiency of the parabolic collector [unitless]

Do Outside diameter of the tubes [m]

Qr Radiation heat loss [kJ]

hr Radiation heat transfer coefficients [W⁄ (m2. K)]

rr Rim radius [m]

φr Receiver angle

Al Shaded area [m2]

Ds Shell inside diameter [m]

cp Specific heat capacity [kJ⁄ (kg. K) ]

cp, w Specific heat of water [kJ⁄ (kg. K) ]

cp, t Specific heat of teff [kJ⁄ (kg. K) ]

Pr Stands for the tube layout correction factor

Ts Surface temperature [K]

As Surface area of the parabolic trough collector [m2]

T∞ Surrounding or ambient temperature [K]

K Thermal conductivity [W⁄m. K]

CL Tube layout constant (constant factor) 0.87 for 30° and 60° [unitless]

L Tube length [m]

CTP Tube count calculation constant for one tube pass 0.93 [unitless]

K Thermal conductivity of the aluminum tube [W⁄m. K]

1 Introduction

1.1 Background

The sun, an inexhaustible source of energy, plays a crucial role in determining the amount of solar energy received by an area, influenced by factors such as time of day, season, cloudiness, and proximity to the Earth's equator. Solar energy, derived from the sun's rays, stands as the largest renewable energy source. In Ethiopia, solar irradiation exhibits regional and seasonal variations, ranging from 5 to 7.5 kWh/m2/day, with an average of 5.2 kWh/m2/day. The seasonal range spans from 4.55 to 5.5 kWh/m2/day, with values as low as 4.25 kWh/m2/day in the extreme western lowlands and reaching as high as 6.25 kWh/m2/day in the Adigrat area of northern Ethiopia [1].

Despite the abundance of solar energy, Ethiopia heavily relies on traditional biomass resources, such as dung and fuelwood, for household energy, with 96 % of the population dependent on them. This heavy dependence on biomass leads to deforestation, soil erosion, and land degradation. Additionally, conventional energy sources are depleting rapidly, and the growing population and increasing human activities put additional strain on the already limited energy resources [2].

Injera, a staple food in Ethiopia and Eritrea, is consumed daily by a majority of the population. It is typically served on a flat utensil and enjoyed with various toppings or stews known as "wat" [3]. However, the baking process for Injera is the most energy-consuming process in Ethiopian households, accounting for approximately 60 % of their energy consumption [3]. Currently, the majority of households rely on inefficient biofuels such as fuelwood, agricultural residue, and dung cakes for baking Injera. In urban areas, some households use electricity, and public institutions utilize conventional electric clay stoves for baking Injera.

The traditional method of baking injera, a staple food in Ethiopia, involves significant energy consumption and health hazards, prompting exploration into alternative baking techniques. In Ethiopia, injera is consumed widely, with its preparation deeply ingrained in the culture, utilizing various energy sources for baking. Among these, the Solar Thermal Injera Baking Method has emerged as a promising solution, harnessing radiant energy from the sun for heat generation. This method employs a solar collector to convert solar radiation into heat energy, subsequently circulated throughout the baking system via a heat transfer fluid [[4], [5], [6]].

This study focuses on the design of a Solar Thermal System tailored for Injera Baking, specifically for the Mekelle University Main Campus Student Cafeteria. By integrating solar technology into the baking process, the aim is to reduce reliance on conventional energy sources, mitigate environmental impact, and improve baking efficiency. Previous research in this field has explored various aspects, from system design and development to enhancing efficiency.

The investigation seeks to contribute to the advancement of sustainable energy solutions within the culinary domain, addressing both environmental and socioeconomic considerations. Through the design and implementation of a Solar Thermal Injera Baking System, the study endeavors to offer insights into the feasibility and efficacy of integrating solar technology into traditional electrical culinary practices, particularly in the context of university cafeterias.

Unfortunately, conventional electric clay stoves consume a significant amount of power and have long baking times due to their low thermal conductivity and excessive thickness. Previous studies indicate that Injera requires temperatures ranging from 180 to 220 °C for proper baking [7], but Tesfay et al. [8] have successfully reduced this range to 135–160 °C (see Table 4). This reduced temperature range presents an opportunity to revolutionize the Injera baking process in Ethiopia by employing a modified clay stove powered by solar energy. Goitom designed a solar-powered Injera baking system that utilizes parabolic troughs to transfer heat to oil, which is then circulated through the space below the baking pan in the kitchen with a clay stove [9].

Mekelle, the capital city of the Tigray regional state, holds significant importance in this context. This Situated at 13° 50′ N latitude and 39° 42′ E longitude, the city's impressive elevation of 2212m above sea level results in a tropical semi-arid climate, influencing the lives of its residents and the surrounding environment. Mekelle experiences an average annual rainfall of 450 mm, following a distinct unimodal pattern. From June to August, the rainy season brings refreshing deluges that nourish the land and vegetation, followed by an extended dry season from September to May, characterized by limited precipitation and arid conditions [10].

At present, the main student cafeteria at Mekelle University relies on 50 conventional electric Mitads to fulfill the daily Injera consumption of 5500 students. However, each Mitad consumes 3.7 KW of electricity and experiences a heat loss of 50–60 % [11]. Moreover, the traditional clay used in these Mitads has low thermal conductivity and high heat capacity. The baking process in electric Mitads occurs within the temperature range of 130–220 °C, consuming approximately 1.18 MJ/kg of Injera, with an average specific useful energy consumption of 0.48MJ/Injera and a baking time of 180–240 s [11]. This energy-intensive system places a significant burden on the national grid and incurs high costs. Therefore, the objective of this work is to replace the conventional electric Mitad baking system at Mekelle University student cafeteria with a solar thermal system.

Several attempts have been made to design a solar thermal Injera baking system [1]. utilized a circular coil pipe as a heat source for the baking pan, without an energy storage tank. In this study, a circular cylinder (oil gallery) is employed to uniformly distribute oil on the baking pan, along with a thermal storage tank to ensure continuous and regular energy flow, preventing pump impeller failure. The new design aims to use radiant energy from the sun, converting it to heat energy by employing a solar collector to lower the Injera baking temperature through the reduction of the baking plate's thickness and the use of high thermal conductivity materials.

To optimize the utilization of solar energy resources, the orientation of the parabolic trough is crucial. Since Ethiopia is located in the Northern Hemisphere, the collectors should face south to maximize total energy collection. Another important angle is the tilt angle, which is set to the latitude of the collector's location. Therefore, the collector is tilted at approximately 14°, equal to the latitude of Mekelle. Mekelle's proximity to the equator results in the solar zenith angle being close to zero, with direct radiation accounting for around 85 % of the total insolation striking the ground, while diffuse radiation accounts for approximately 15 % due to water vapor, dust, pollutants, and clouds.

The optical analysis of the parabolic trough collector, including parameters such as focal length, rim radius, height of the parabolic trough curve, curve length of the parabola surface, surface area, shaded area, aperture area, geometric factor, and concentration ratio, will be calculated. The collectors will be equipped with a continuous single-axis horizontal tracking system that automatically adjusts daily, and a suitable type of heat exchanger (receiver) will be designed to be compatible with the parabolic trough collector. Considering Mekelle's northern hemisphere location, the parabolic troughs should be oriented towards the South Pole. The temperature distribution on the baking pan and oil gallery surface will be simulated using the ANSYS Fluent Solver, while Soltrace will simulate the solar thermal heat flux generated in the receiver and it should be uniform on the receiver or heat exchanger for successful baking purpose.

The research will be validated against previous related work, providing a comprehensive assessment of its significance. Traditionally, clay stoves have been known for their low thermal conductivity, resulting in excessive energy consumption and prolonged baking times. However, through the utilization of a modified clay stove combined with solar energy, a breakthrough was achieved in reducing the baking temperature range for Injera from 180-220 °C to 135–160 °C. Remarkably, the study demonstrated that baking Injera on an aluminum surface at temperatures as low as 130–150 °C is feasible without compromising its quality. This groundbreaking discovery paves the way for the design of energy-efficient frying pans and a reduction in heat storage requirements. By implementing strategies such as decreasing plate thickness and incorporating materials with high thermal conductivity, the optimization of the baking temperature yielded exceptional results, including uniform bubble distribution, non-stick properties, and an overall excellent texture. These significant findings represent crucial advancements in the development of home-based and community-based designs and technologies, effectively addressing challenges related to escalating energy prices and the pressing demand for clean energy solutions.

1.2 Research gap

This research aimed to design a solar thermal system for injera baking at Mekelle University's student cafeteria by using a high heat transfer fluid and storing phase change materials (PCM) for continuous energy flow during baking. Previous studies primarily used steam as the heat transfer fluid, which could lead to pressures up to 40 bar and cause corrosion due to steam condensation, thus reducing system lifespan [[4], [5], [6]]. Additionally, there has been insufficient research on oil-based solar injera baking systems, despite the high consumption of injera in Ethiopia. Conventional clay stoves in previous studies required significant preheating power and extended baking times. This research addresses these gaps by designing a solar thermal baking system with oil storage capacity to maintain a steady energy flow and prevent pump impeller failure, incorporating PCM in the receiver as a backup heat source. The new design employs a circular cylinder (oil gallery) instead of a coiled pipe beneath the baking plate to ensure uniform temperature distribution, resulting in better quality and texture of injera. The baking pan is made of non-stick anodized aluminum with low thickness due Anodized aluminum, with its thick, non-reactive oxide layer, prevents interactions with acidic foods like teff dough, enhances food safety and taste quality, improves durability and corrosion resistance, retains excellent thermal conductivity for even heat distribution, and is easier to clean and often dishwasher safe so thereby reducing preheating power and baking time.

1.3 The need of study

The need of this study lies in its potential to introduce renewable solar energy as a viable alternative to conventional electricity sources, particularly in regions like Ethiopia heavily reliant on hydropower, which can be inconsistent during drought seasons. By focusing on the design of a Solar Thermal Injera Baking System for the Mekelle University Main Campus Student Cafeteria, this research not only addresses the immediate need for sustainable energy solutions in culinary practices but also contributes to broader environmental and economic goals.

Firstly, the study showcases the feasibility of harnessing solar energy for culinary purposes, illustrating how solar thermal technology can effectively power the baking process. This not only reduces reliance on traditional energy sources but also mitigates environmental emissions associated with electricity generation, thus promoting sustainability.

Moreover, the implementation of solar energy systems has the potential to significantly lower monthly electricity bills for institutions like universities, offering long-term cost savings and budget stability. This economic benefit is particularly crucial for educational institutions facing budget constraints and seeking efficient resource management strategies.

Overall, this study serves as a practical demonstration of the benefits of renewable energy integration in everyday practices, highlighting its capacity to address energy challenges, reduce environmental impact, and foster economic sustainability. By showcasing the feasibility and advantages of solar thermal technology for injera baking, it paves the way for wider adoption of renewable energy solutions in culinary settings, contributing to a more sustainable future.

1.4 The novelty and innovation of the present study

The study introduces a novel approach to replacing conventional electric baking with a solar thermal system. Utilizing anodized aluminum plates for the Mitad, the system lowers the required baking temperature to 130–150 °C, enhancing energy efficiency while maintaining injera quality. The innovative use of parabolic trough collectors to harness solar energy, combined with phase change materials for thermal storage, ensures a consistent and reliable heat source. CFD and Soltrace simulations optimize temperature distribution and solar thermal heat flux, ensuring uniform baking conditions. This design, capable of baking 11,000 injera daily, addresses significant energy demands sustainably, offering substantial environmental and economic benefits. By integrating renewable energy into traditional culinary practices, the study demonstrates a scalable, practical solution with potential for widespread adoption, promoting sustainability and reducing energy costs.

1.5 The major contributions of the present study

The study offers a pioneering solution to the energy-intensive process of injera baking by introducing a solar thermal system. Its innovative use of anodized aluminum plates for the Mitad reduces baking temperatures to 130–150 °C, enhancing energy efficiency without compromising injera quality. Integration of phase change materials ensures a steady heat supply, addressing intermittency issues. Through meticulous simulations, the system achieves uniform baking conditions, validated by its capacity to bake 11,000 injera daily. Beyond practical scalability, this approach fosters sustainability, reducing environmental impact and operating costs while exemplifying a paradigm shift towards renewable energy integration in culinary practices.

2 Description of the system

The study focuses on the design of a solar thermal system, which consists of three main sections: the solar collector section, the thermal energy storage section, and the baking section. The primary source of energy for the system is solar energy. The design incorporates a parabolic trough solar collector with a heat exchanger located at its focal line. This heat exchanger contains phase change material (PCM)-based thermal storage and heat transfer oil(see Fig. 1).Fig. 1 Schematic diagram of solar Injera baking system configuration.

Fig. 1

The process begins with the solar collector section, where the parabolic trough solar collector harnesses solar energy and directs it to the heat exchanger. The heat exchanger heats the transfer oil by utilizing the concentrated solar energy. The heated oil is then transferred and stored in a hot oil storage tank, which acts as a reservoir for the hot oil.

In the baking section, an array of Injera baking Mitad is supplied with hot oil from the hot oil storage tank. The hot oil exchanges heat with the Mitad during the Injera baking process. As the relatively cold oil returns from the Mitad, it is stored in a cold oil storage tank, ready for the next charging and discharging phases of the 6-h baking operation.

Flow control mechanisms are employed to ensure that the hot oil is stored in the hot oil storage tank during the preheating state. This allows the system to have a "hot start" on the first day of preheating, ensuring that it is ready to fulfill the required Injera demand on the following day.

The baking process itself involves the convection heat transfer mechanism, where heat is transferred from the hot oil to the baking plate. The baking plate then conducts the heat to the dough, resulting in the evaporation and boiling of the water inside the dough. This causes the dough to lose a percentage of water through evaporation and form characteristic "eyes" due to the baking process.

Overall, the solar thermal system operates by effectively utilizing solar energy to heat the oil, which is then used for baking Injera. The incorporation of thermal storage allows for continuous operation and ensures that the system can meet the required Injera demand. The study aims to demonstrate the feasibility of this system as an efficient and sustainable alternative for Injera baking, contributing to reduced energy consumption and environmental impact.

3 Methodology of the system

The solar thermal system will be designed with three main sections: the solar collector section, the thermal energy storage section, and the baking section. The design process will involve calculating energy utilization, heat loss, and selecting appropriate heat transfer fluid and phase change material (PCM). In addition, the configuration of system components, heat exchanger, and sizing of the solar collector will be carefully considered to ensure optimal performance.

The solar energy-based Injera baking system, as outlined in Appendix A, is composed of several key elements. These include the baking section, the pipe network, the cold and hot storage tanks, the receiver, and the parabolic trough solar collector. The baking section consists of an array of 92 Mitads, each constructed with an Anodized aluminum plate measuring 0.56m in diameter and 0.01m in thickness. Each Mitad is connected to an oil gallery underneath, which supplies hot oil to meet the energy demand during the baking process.

Anodized aluminum offers notable advantages over cast iron, clay, and non-coated aluminum, particularly in cookware applications. Compared to cast iron, anodized aluminum is significantly lighter and easier to handle, while providing superior heat conductivity and even heat distribution without requiring regular seasoning to prevent rust. Unlike clay, which can be fragile and prone to cracking, anodized aluminum is highly durable and heats up quickly, making it more efficient for everyday cooking. Additionally, anodized aluminum's non-reactive surface prevents interactions with acidic foods, a problem commonly associated with non-coated aluminum, which can corrode and alter food flavors [12].

The heat exchanger features a focal line that contains a PCM-based thermal storage and heat transfer oil. The heated oil is then transferred and stored in the hot oil storage tank, which provides the necessary energy during the baking process. The relatively cooler oil is returned and stored in a cold oil storage tank, from where it is pumped to the solar collector system for subsequent charging and discharging phases of the application.

To analyze the temperature of the Injera baking pan, ANSYS-fluent solver is employed, utilizing energy equations, continuity equations, and momentum equations. Furthermore, Soltrace is used to simulate the average solar heat flux on the receiver and the heat distribution on the receiver. Representative days of the year are selected based on a satellite-based daily solar radiation estimation method [[13], [14], [15]]. These simulations provide valuable insights into the performance and effectiveness of the system.

By incorporating these design considerations and simulations, this solar thermal system demonstrates its potential to offer a sustainable solution for Injera baking, reducing energy costs, and minimizing environmental impact.

3.1 Energy distribution of injera baking system

The energy input required for a single Mitad, which includes both the baking plate and the oil gallery, is a combination of various factors. It comprises the useful energy needed for the baking process itself, the stored energy within the baking plate and oil gallery, and the surface heat losses from the external surface of the baking plate and oil gallery assembly.

To obtain this energy, the system utilizes the hot oil stored in the hot oil tank. The hot oil, which acts as the primary energy source, supplies the necessary heat to fulfill the energy requirements of the baking process.

By efficiently utilizing the energy stored in the hot oil, the system ensures that the baking plate and oil gallery receive the appropriate amount of energy for optimal performance. This energy input is crucial for achieving the desired baking results and maintaining the required temperature levels throughout the baking operation.

The determination of the useful energy required for baking Injera is based on previous studies [3,7]. It can be calculated using the following Eq. (1)(1) Qu=(md×CP,d)×(Tb−Ta)+(mw)hvap

In addition, the stored energy within the Mitad was determined using the following Eq. (2)(2) Estored=m×Cp×ΔT

Furthermore, the convective and radiation heat losses were calculated as follows in Eq. (3)(3) Qc=hc×Ap(Tp−Ta)andQr=hr×Ap(Tp−Ta)

Finally, the thermal efficiency of the single Mitad was determined using the following Eq. (4)(4) ηth=usefulenergyduringthewholebakingprocessinputenergyofbakingprocess

3.2 Sizing of the hot oil and cold oil tanks

The hot oil tank plays a crucial role in the solar thermal system for 1-h baking operations. Through careful analysis, it was determined that the optimal volume for the hot oil tank is 6.374 m3, considering the recycling process until completion. This sizing decision was made with several objectives in mind, including reducing the cost of storage tank materials, minimizing pump power requirements, and simplifying the control system.

To accurately assess the system's performance, the total input energy was calculated by considering various factors. This included evaluating the stored energy by both the hot oil storage surface and the insulator surface. Additionally, the calculations accounted for heat losses from the insulator surface and the total energy consumed by the baking area.

In the baking process, the cold oil produced in the baking area is directed into a separate cold oil storage tank. This tank is sized to optimize the volume for 20 min of baking operation. To fulfill the 1-h baking requirement, the cold oil circulates three times through the heat exchanger (receiver). This circulation process ensures efficient utilization of energy resources and enables a consistent baking process.

3.3 Sizing of the receiver (heat exchanger)

The selection of the shell and tube heat exchanger for the solar thermal system was based on several advantageous factors. This type of heat exchanger was chosen due to its compatibility with the fixed linear parabolic trough collector. It offers a substantial ratio of heat transfer area to volume and weight, making it well-suited for the system's requirements. Additionally, the shell and tube heat exchanger allows for easy construction in various sizes and facilitates convenient cleaning and replacement processes [16].

In the system design, the heat exchanger operates as follows: The oil, initially at a temperature of 100 °C, is pumped to the tube side of the heat exchanger. Through the heat exchange process, the oil is heated and reaches a temperature of 168 °C. Subsequently, the oil is transferred to the hot oil storage for further utilization. On the other hand, the shell side of the heat exchanger contains the molten solar salt, which maintains a constant temperature of 220 °C. The fixed shell side ensures the stability of the solar salt temperature throughout the system in Fig. 2.Fig. 2 Temperature profile heat exchanger.

Fig. 2

The design of the shell and tube heat exchanger involved the application of the Log Mean Temperature Difference method, a widely used approach [17]. By utilizing this method, the heat duty of the heat exchanger for a 1-h baking operation was determined to be 337.8 kW. Additionally, the required heat transfer area, was calculated in Eq. (5) the Log Mean Temperature Difference method was calculated in Eq. (6)(5) Q˙=UAsFΔTlmCF

(6) ΔTlmCF=ΔT1−ΔT2ln(ΔT1ΔT2)

To provide the necessary heat transfer area, the number of tubes required, was calculated using Eq. (7)(7) Nt=Asπ×Do×L

Furthermore, the inside diameter of the shell, was determined by Eq. (8)(8) Ds=0.637CLCTP(A×Pr2×DoL)

In order to optimize the performance of the solar thermal system, the appropriate volume of the shell and tube heat exchanger was carefully determined, taking into account its 20-min working capacity. This volume encompasses various components, including the volume of the hot oil, the volume of the solar salt mixture, the clearance volume required to accommodate the expansion of the solar salt mixture, and the volume occupied by the tubes within the shell and tube heat exchanger.

To accurately assess the system's energy requirements and efficiency, the total input energy necessary for the heat exchanger storage was calculated. This calculation considered multiple factors, including the stored energy on the storage surface, the stored energy on the insulator surface, the surface heat loss from the insulator, and the oil stored within the heat exchanger itself. These energy components are crucial in evaluating the overall performance of the system.

It is important to note that the energy required for the heat exchanger storage is supplied from the concentrated solar collector. This emphasizes the role of the concentrated solar collector as the primary source of energy for the system. By accurately determining the appropriate volume of the shell and tube heat exchanger and calculating the total input energy, the system can effectively utilize the concentrated solar energy and optimize its storage and distribution within the heat exchanger.

3.4 Design of the solar collector system

The design of the solar collector system with concentrating collectors was carefully developed to meet the desired temperature requirements. To achieve this, the parabolic trough collector system was chosen for its advantageous features such as compatibility with the linear receiver (heat exchanger), ease of operation in tracking the sun, cost-effectiveness in terms of materials, availability in various sizes, and proven success in low and medium-temperature applications [18]. This system utilizes the parabolic trough collector to concentrate solar radiation onto a half-insulated receiver, which functions as a heat exchanger. The receiver is designed with oil and PCM (Phase Change Material) to minimize heat loss from its surface, as depicted in Fig. 3. By harnessing the capabilities of the parabolic trough collector and employing effective insulation techniques, the solar collector system can efficiently capture and utilize solar radiation to achieve the desired temperature levels for the intended applications (see Fig. 4).Fig. 3 Side and front view of a parabolic trough solar collector and receiver system layout respectively.

Fig. 3

Fig. 4 Cross-section of a parabolic trough collector with a circular receiver [19,20].

Fig. 4

3.4.1 Description of the working site

The performance test of the solar thermal system was carried out at Mekelle University, which offers an ideal location characterized by short rainy seasons and predominantly dry weather conditions with clear sky radiation. To assess the system's effectiveness in harnessing solar energy, Table 1 presents a comprehensive solar energy profile, detailing the monthly average of direct solar energy radiation specifically recorded at the Mekelle University site [13]. This data provides valuable insights into the solar resource availability and helps in evaluating the system's potential to harness solar radiation efficiently.Table 1 The monthly average of direct solar energy radiation at the Mekelle University site [13].

Table 1Month	Jan	Feb	Mar	Apr	May	Jun	July	Aug	Sep	Oct	Nov	Dec	
Horizontal surface kWh/m2	8.04	7.69	7.01	7.01	6.63	5.71	4.81	4.51	5.9	7.19	8.07	8.03	

The solar-based Injera baking system is specifically engineered to operate actively for approximately nine months per year, spanning from September to May. Based on the data provided in Table 1 [13], the average daily radiation during this operational period at the Mekelle University site was estimated to be 7.285 kWh/m2. The key design aspects of the parabolic trough primarily revolve around the collector area and its geometry, as these factors play a crucial role in determining the overall size of the collector. To ensure optimal performance, the required aperture area of the parabolic trough collector was computed using appropriate calculations and considerations. Eq. (9)(9) Aap=Q˙absηoIB

Based on [13,18], the average daily solar radiation during this period was recorded as 795 W/m2, while the optical efficiency of the parabolic trough collector was measured to be 0.8.

The focal length of the parabolic trough collector was solved by Eq. (10) [[19], [20], [21]].(10) f=Wa/4tanφ2

The collector has parabola shape with radius (rim radius) was calculated by Eq. (11) [[19], [20], [21]].(11) rr=2f/1+cosφr

The height of the parabolic trough curve was calculated by Eq. (12) [19,21]. The length of the parabolic trough curve as well as the diameter of the cylindrical receiver was determined to be 100m and 0.212m, respectively.(12) Hc=Wa2/16f

The arc length parabolic trough curve (curve length of parabola surface was calculated by Eq. (13) [19,21].(13) Sp=Hp2[secφr2tanφr2+ln(secφr2tanφr2)]

The surface area of the parabolic trough collector was calculated by Eq. (14)(14) As=Sp×L

The geometric factor is the ratio of shaded area (total loss in aperture area) to the aperture area by Eq. (15) [19,21].(15) Af=Al/Aa

The total loss in the aperture area of the collector was calculated by Eq. (16) [19,21].(16) Al=23WaHc+fWa[1+Wa248f2]

Finally, the aperture area of the parabolic trough collector, was calculated by Eq. (17)(17) Aa=Daeff×L=(Wa−Dr)×L

The concentration ratio is quantified the level of light energy concentration achieved by the collector. In this particular system, the receiver tube's projected area was designed to form a rectangle with dimensions of (receiver diameter × signifies the length). The concentration ratio is calculated by Eq. (18) [19,21].(18) CR=AaAr=DaeffDr

4 Result and discussion

The proposed geometrical dimensions of the parabolic trough were determined through careful analysis; taking into consideration various design factors. These parameters, along with their corresponding values, are summarized in Table 2.Table 2 Estimated parameters of parabolic trough collector.

Table 2Calculated parameters	Results	
Focal length	1.71m	
Rim radius	2.91m	
Height of the parabolic trough curve	1.21m	
Curve length of parabola surface	8.05m	
Surface area	805.1 m2	
Shaded area	16.8 m2	
Aperture area	532.9 m2	
Geometric factor	0.031	
Concentration ratio	16.88	

The results of the optical analysis conducted on the parabolic trough collector indicate a close resemblance to the Euro Trough 100 (ET-100) model, which is readily available on the market [22,23]. The ET-100 model, composed of 8 collector modules each measuring 12 m in length and featuring a total aperture area of 545 m2, was selected. Notably, these collector modules are equipped with a continuous single-axis horizontal tracking system that facilitates automatic daily tracking Table 3.Table 3 Comparison of the results of the present research work with earlier/previous studies.

Table 3Design of solar thermal system for Injera baking application, for the case of Mekelle University student cafeteria	Design and development of solar thermal Injera baking: steam based direct baking [8]	Performance investigation of solar powered Injera baking oven for indoor cooking [7]	
Material used: Aluminum Mitad	Material used: Modified clay Mitad	Material used: Ceramic Mitad	
Collector: Parabolic trough	Collector: Parabolic dish	An electric heater is used in experimental work to heat the oil in a tank	
Working fluid: Shell heat transfer fluid oil S2	Working fluid: Steam	Electric current is used as the working fluid	
PCM (solar salt) is stored inside the shell of the shell and tube heat exchanger (receiver)	PCM (solar salt) is not stored	PCM (solar salt) is not stored	
Heat transfer process is governed by forced circulation using an oil transfer gear pump	Heat transfer process is governed by natural circulation boiling-condensation between the receiver and stove	Heat transfer process is governed by forced circulation	
Oil flows freely within the cylinder (oil gallery)	Steam flows within a circular coil	Hot oil storage tank works as a heat exchanger	
Optimal baking temperature (130–143 °C) was simulated using CFD	Optimal baking temperature for Injera: 135–160 °C	Optimal baking temperature: 180–220 °C	
Baking mechanism: Indoor baking	Baking mechanism: Outdoor baking		
The flow of oil is regular and continuous due to the pump, temporary oil storage, and flow control valve	Due to the working fluid being steam, high pressure (30–40 bar) is required in the heat transfer loop		
The flow of oil is easily controlled and there is low heat loss during transport compared to steam	Based on technical and safety concerns, this method is not widely used in cooking and baking		
Heat-up time: 30 min	Heat-up time: 45 min	Initial heat-up time for Mitad: 25 min	
Baking and retaining time: 180 s	Baking and retaining time: 150 s	Baking and retaining time: 300 s	

Table 4 Comparative analysis (quantitative).

Table 4Aspect	This Research	[8]	[7]	
Material Used	Aluminum Mitad	Modified clay Mitad	Ceramic Mitad	
Collector	Parabolic trough	Parabolic dish	Electrical heater	
Working Fluid	Shell heat transfer fluid oil S2	Steam	Electric current	
PCM (Phase Change Material)	Solar salt stored inside the shell	Not stored	Not stored	
Heat Transfer Process	Forced circulation using oil pump	Natural circulation boiling-condensation between receiver and stove	Forced circulation using oil pump	
Heat-Up Time	30 min	45 min	25 min	
Baking and Retaining Time	180 s	150 s	300 s	
Optimal Baking Temperature	130–143 °C	135–160 °C	180–220 °C	
Baking Mechanism	Indoor baking	Outdoor baking	Indoor baking	

For the proposed solar-based Injera baking system, extensive calculations were performed to determine the necessary dimensions and specifications of the receiver. It was found that a total receiver volume of 3.550 m³ is required to support 20 baking operations. The receiver has a length of 100 m and a diameter of 0.212 m Additionally; the parabolic trough collector was designed with a length of 100 m, an aperture width of 5.76 m, and an aperture area of 532.9 m2. Through further analysis, the focal length was estimated to be 1.71 m, while the height of the parabolic trough reached 1.21 m. These parameters were derived based on the calculations and considerations made during the research. This design parameter is similar to the market-available ET-100 model. To provide visual representation, Fig. 5 illustrates the structure of the ET-100 model, available in the market which serves as a reference for the proposed design.Fig. 5 The structure of ET100 parabolic trough collector [24].

Fig. 5

The shell and tube heat exchanger design parameters, including the heat transfer area, shell inside diameter, number of tubes per pass, and heat transfer coefficients, were calculated to be 30.7 m2, 0.212 m, 3, 283.1 (W/m2°C), and 543 (W/m2°C) respectively. These calculations were crucial in optimizing the performance of the heat exchanger.

The results of the study demonstrate significant improvements in thermal efficiency compared to previous experimental work conducted by Hailu [11]. The new design achieved a thermal efficiency of 57.4 % per cycle, representing a notable 19.4 % increase. This enhancement in efficiency highlights the effectiveness of the modifications made to the heat exchanger design.

Furthermore, the modified design showcased a reduced useable energy consumption of 380 KJ, indicating a 20.83 % decrease compared to Hailu's design. This reduction in energy consumption is a valuable outcome, as it contributes to the overall energy efficiency and sustainability of the solar-based Injera baking system.

4.1 Energy distribution in single Mitad

The total input energy required for the first Injera baking cycle of each Mitad was calculated as the sum of the useful energy for the baking process, stored energy in the mited itself, and heat losses, which amounted to 1085 KJ. The thermal efficiency of a single Mitad was determined by the ratio of the useful energy for the baking process to the input energy for the baking process, which was found to be 73.4 %. Fig. 6 illustrates that a significant portion of the energy distribution is in the form of stored energy in the baking plate, which can be attributed to the high specific heat capacity of aluminum compared to other metallic materials.Fig. 6 Energy distribution of single Mitad.

Fig. 6

The calculation of the total input energy required for the first Injera baking cycle of each Mitad was a crucial aspect of the study. It encompassed the useful energy for the baking process, the stored energy in the Mitad itself, and the heat losses, resulting in a total input energy of 1085 KJ. This comprehensive analysis provided valuable insights into the energy requirements of the baking system.

The thermal efficiency of a single Mitad was determined by evaluating the ratio of the useful energy for the baking process to the input energy for the baking process. The findings revealed a thermal efficiency of 73.4 %, indicating the effectiveness of the Mitad in converting input energy into useful energy for the baking process. This high thermal efficiency underscores the efficiency of the system in utilizing energy resources.

Fig. 6 visually represents the energy distribution within the system. It is evident that a significant portion of the energy is stored in the baking plate itself. This can be attributed to the high specific heat capacity of aluminum, which enables it to retain and store a substantial amount of energy during the baking process. Aluminum is an excellent material for baking due to its high thermal conductivity, which allows it to heat up quickly and distribute heat evenly across the surface, ensuring uniform baking. Unlike cast iron, which is slower to heat and cool but excels at retaining heat, aluminum responds rapidly to temperature changes, making it ideal for recipes that require precise heat control. Even though aluminum does not store as much heat as cast iron, it is still the better choice for baking injera. Additionally, aluminum is lightweight and resistant to corrosion, making it easier to handle and more durable in the kitchen compared to the heavier, more heat-retentive cast iron. Therefore, aluminum is preferred for its efficiency and ability to produce consistent results in the injera baking process.

The investigation focused on assessing the energy requirements and losses associated with the baking area during a 1-h baking operation, yielding significant findings. The calculated energy requirement for the baking area amounted to 777 MJ, indicating the substantial energy input necessary for the baking process. Additionally, the study determined the energy storage capabilities of the hot oil storage surface and the insulator material, resulting in stored energy values of 43.72 MJ and 9.46 MJ, respectively. Considering the insulation, the estimated heat loss from the insulated surface was determined to be 15.87 MJ, highlighting the need to minimize such losses for improved energy efficiency. Consequently, the total input energy required by the hot oil storage for a 1-h baking operation was found to be 846.05 MJ, a significant value that Emphasizes the energy demand of the system. It is worth noting that this energy is supplied from the heat exchanger or receiver, emphasizing the role of efficient energy transfer in the baking process.

4.2 Energy distribution in receiver

The investigation delved into assessing the energy dynamics of the heat exchanger in the context of a 20-min baking operation, yielding significant results and implications. Notably, the study determined the energy stored within the heat exchanger and insulator material to be 80.09 MJ and 28.79 MJ, respectively, showcasing their crucial role in the overall energy management of the system. Moreover, the estimated heat loss from the insulated surface amounted to 14.02 MJ, emphasizing the need for efficient insulation strategies to mitigate energy losses. Specifically, the stored energy within the hot oil in the heat exchanger for a 20-min baking operation was found to be 282.6 MJ, a substantial amount that contributes significantly to the energy requirements of the process. Furthermore, the calculated input energy required by the heat exchanger (receiver) for the 20-min baking operation was 405.5 MJ. Extrapolating this to a 1-h baking operation, the total input energy demanded by the heat exchanger was determined to be 1216.515 MJ. Importantly, this energy is sourced from the parabolic trough solar collector, whose efficiency was established to be 80 %.

4.3 The distribution of temperature on the baking pan during the heat-up time and baking process

The investigation yielded valuable insights into the temperature dynamics of the baking pan and its crucial role in achieving optimal baking conditions for Injera. As per the recommended standards, the top surface of the baking pan should maintain a temperature range of 130–220 °C. Fig. 7 provides a visual representation of the surface temperature of the baking pan and its corresponding heating time. Notably, it was found that the maximum required temperature of 130 °C was attained within 30 min, indicating the efficiency of the heating process. Subsequently, the surface temperature of the baking pan remained stable at this optimal temperature throughout the baking duration, showcasing the effectiveness of the system in maintaining consistent conditions. The absence of any temperature increase over time indicates the ability to sustain the desired temperature range without deviation. The initial heat-up phase involved gradually raising the temperature of the Mitad baking plate from an ambient temperature of 20 °C. This was achieved by continuously supplying hot oil from the hot oil storage into the hot oil gallery beneath the baking plate. However, it is important to note that the baking plate's constant temperature of 130 °C was maintained due to the inherent heat losses resulting from convective and radiative processes. This stable temperature range is critical in ensuring the desired texture and characteristics of the Injera, including the presence of uniform bubble eyes and proper adherence to the Mitad.Fig. 7 Heating time and temperature distribution on the baking pan surface.

Fig. 7

Fig. 8 provides additional insights into the transient temperature profile of the baking pan surface throughout the heat-up and baking process. The analysis reveals that it takes approximately 2 min to reach a baking temperature of 94 °C. Subsequently, a retaining time of 1 min is necessary to achieve the desired temperature of 130 °C, as recommended [25]. This controlled heat-up phase ensures that the baking pan surface reaches the optimal temperature for producing high-quality Injera. Furthermore, it is worth noting that after each baking cycle, both the retaining and baking times are gradually reduced.Fig. 8 The baking time and temperature distribution of the pan during baking.

Fig. 8

The initial heat-up of the baking pan takes 30 min to achieve a surface temperature of around 130 °C. It will then take 2 min to bake each injera, during which the surface temperature will drop to 94 °C due to heat loss and energy consumption. To bake the injera properly, a recovery time of 1 min is needed to bring the surface temperature back to 130 °C, making it ready for the next injera. This cycle of temperature fluctuations will continue until the required number of injera is baked.

During the baking process of Injera, the temperatures of the baking pan and the Injera closely align. However, at the beginning of the baking cycle, there is a notable drop in the temperature of the baking pan. This decrease in temperature can be attributed to the introduction of the dough onto the surface of the pan. To gain a more detailed understanding of this temperature variation, Fig. 9 offers a closer examination of the temperature changes occurring on the surface of both the baking pan and the Injera during the initial baking phase. By analyzing this temperature profile, it becomes evident how the heat is transferred from the pan to the Injera, resulting in the gradual increase in temperature of the Injera as it undergoes the baking process.Fig. 9 The temperature profile of Injera and the baking pan during the first baking cycle.

Fig. 9

4.4 Temperature distribution of baking pan and gallery surface with CFD

In Fig. 10, the temperature distribution along the radial direction of the baking pan model is presented through a temperature contour. The analysis reveals that the highest temperature is concentrated around the midpoint of the baking pan's radius, gradually decreasing towards both the center and the edge. Specifically, the center of the baking pan exhibits a temperature of approximately 143.5 °C, while the temperature at the edge reaches around 138.5 °C. This temperature distribution has implications for the baking process of Injera. To ensure an even temperature distribution on the Injera, it is recommended for bakers to start rotating the dough from the edge of the Mitad towards the center. Although the temperature at the edge is slightly lower than at the center, it remains above the recommended baking temperature, thereby facilitating proper baking. Importantly, the observed temperature difference between the center and the edge is 5 °C, which is significantly lower compared to the temperature deviation of 18 °C reported in previous studies on the center-to-edge temperature distribution in the Mitad [17,26]. To ensure the reliability of the temperature distribution analysis in Fig. 10, a grid independence study was conducted. Starting with a coarse grid and refining it in stages, the temperature distributions were compared at each step. The study confirmed grid independence when further refinement resulted in less than a 1 % change in temperature values. The final optimal grid resolution revealed a maximum temperature of approximately 143.5 °C at the center and 138.5 °C at the edge. This confirms the accuracy of the 5 °C differences, which is significantly lower than the 18°C-deviation reported in previous studies, providing a solid basis for practical recommendations on baking Injera.Fig. 10 Temperature distribution of the baking pan surface.

Fig. 10

Fig. 11 provides an insightful temperature distribution analysis along the radial direction of the oil gallery model, as depicted by the temperature contour. The findings reveal that the highest temperature is concentrated near the midpoint of the baking pan's radius, gradually decreasing towards both the center and the edge. Specifically, the center of the oil gallery exhibits a temperature of approximately 150 °C, while the temperature at the edge measures around 138.5 °C. This temperature distribution phenomenon can be attributed to the high viscosity of the oil used in the baking system. Due to its properties, the heated oil tends to concentrate at the center and does not readily distribute evenly throughout the oil gallery. Consequently, the temperature at the center is higher compared to the temperature at the edge. A comprehensive grid independence study was conducted to ensure the accuracy of the temperature distribution analysis in Fig. 11. Starting with a coarse grid, the model was progressively refined by increasing the number of grid points, and the resulting temperature distributions were compared at critical locations, such as the center and edge of the oil gallery. The study confirmed grid independence when further refinement led to less than a 1 % change in temperature values, ensuring the results were not influenced by grid size. This optimal grid resolution revealed a temperature of approximately 150 °C at the center and 138.5 °C at the edge, attributed to the high viscosity of the oil, which hinders even heat distribution. The validated temperature profile Highlights the accuracy and reliability of the simulation, providing a credible basis for understanding heat distribution in the oil gallery.Fig. 11 Depicts the temperature distribution of the oil gallery.

Fig. 11

4.5 Heat flux at the absorber tube (receiver)

The findings of the present work reveal that the flux intensity within the receiver tube of the parabolic trough collector is primarily concentrated at its center, as determined by simulating the receiver and parabolic trough using a model in Soltrace software. This concentration is attributed to the excellent concentration ratio achieved by the collector, as illustrated in Fig. 12. The concentration ratio contributes to a uniform distribution of heat flux along the center line of the receiver. This uniform heat transfer is facilitated by the presence of a solar salt mixture inside the shell and oil within the tube. Therefore, maintaining a uniform temperature distribution in the oil within the receiver is crucial for ensuring a continuous supply and achieving a proper baking process, resulting in injera with a good texture.Fig. 12 Simulation result Contour Plot.

Fig. 12

4.6 Economic feasibility of solar injera baking system

Ethiopia's closeness to the equator ensures that it receives enough sunshine hours. Using an electric stove as a point of comparison, the solar Injera baking stove's economic analysis is carried out. The initial investment, fuel expenditure for each technology, salvage values, and maintenance costs are all taken into consideration. When considering the full lifespan of the solar device, the indoor solar injera baking device with storage is substantially less expensive than baking using standard electrical baking technologies. Additionally, according to some studies, the cost of solar energy technologies is declining and rural households are adopting them at a faster rate [27]. Utilizing a solar-based system for baking injera proves to be remarkably cost-effective, offering a compelling blend of economic viability and environmental sustainability. Despite its higher initial investment compared to traditional methods like biomass or electric mitad, the solar-powered approach boasts negligible operating and maintenance costs over its extensive lifespan. With a payback period of just 3.8 years and anticipated operational efficiency for 25 years, the system promises significant long-term savings while reducing dependency on the national grid and mitigating environmental impact. Its ability to slash monthly electricity bills by an impressive 227,197 birr Stress its practicality in both financial and ecological terms, making it a compelling alternative for culinary operations at Mekelle University and beyond.

4.7 Limitation of the study

The study faced several limitations due to the system's parabolic modules, which have a high aperture diameter, long length, and extensive receiver, making it challenging to create a model and simulation that accurately predicts the outlet temperature of oil for representative days of the month using simulation software. Additionally, the study assumes ideal conditions for solar energy availability and uniform baking across all Mitads, potentially overlooking variations caused by weather fluctuations or equipment maintenance. Furthermore, the environmental impact assessment primarily addresses energy consumption, neglecting other sustainability factors such as material sourcing, manufacturing processes, and end-of-life disposal considerations. Addressing these limitations through comprehensive environmental assessments would enhance the study's applicability and provide a more holistic understanding of its feasibility and impact.

5 Validation

Researchers have extensively explored various techniques for designing solar-powered Injera baking systems. In this study, a comparison is made between the design solar thermal Injera baking system and the works presented by Ref. [8], and [7] in their respective papers. Although the common objective of all these research works is to bake Injera utilizing solar energy, there are noticeable quantitative differences in terms of the mechanisms employed and the resulting outcomes between my study and the referenced studies. These distinctions provide valuable insights into the diverse approaches and potential advancements in solar-powered Injera baking technology.

This researcher work stands out as highly significant compared to others due to their innovative use of an aluminum Mitad, parabolic trough collector, and shell heat transfer fluid oil S2. Their approach ensures efficient heat transfer, controlled oil flow, and minimal heat loss during transport. What sets their work apart is their focus on the optimal baking temperature range and practical implementation for mass production. By utilizing forced circulation of oil, they offer a more reliable and scalable solution compared to the use of high-pressure steam or electric current. This research demonstrates a strong understanding of solar thermal Injera baking, providing a practical and sustainable approach for energy-efficient and cost-effective baking processes.

Injera, a traditional Ethiopian dish, typically requires a significant amount of energy when prepared on traditional, energy-inefficient clay stoves. The low thermal conductivity and thickness of the clay stove's mold and baking plate result in high preheating power requirements and long baking times. Previous studies have shown that Injera needs to be baked at temperatures ranging from 180 to 220 °C [7]. However [8], successfully lowered this temperature range to 135–160 °C using a modified clay stove and solar energy as a source, which could have a significant impact on revolutionizing Injera stoves in Ethiopia.

In this research, it was found that Injera can be effectively baked on an aluminum surface, with comparable quality to traditional clay-based pans, at a lower temperature range of 130–150 °C, as long as the heat transfer rate is maintained during baking. This discovery opens up possibilities for designing new and more energy-optimized frying pans for Injera baking, as well as reducing the temperature requirements for heat storage [10]. To achieve this, efforts were made to lower the Injera baking temperature by reducing the thickness of the baking plate and using a material with high thermal conductivity, such as aluminum. The results were successful, with Injera being baked at a temperature range of 130–143 °C, exhibiting a uniform number of eye bubbles, no sticking to the Mitad (baking pan), and a good texture, comparable to previous work. These findings represent significant milestones in the development of home-based and community-based designs and technologies to address the challenges of rising energy prices and the need for clean energy.

This research stands out for its meticulous attention to detail and innovative approach in designing a solar-powered Injera baking system. Unlike previous works, which relied on traditional materials like modified clay or ceramic for the Mitad, this study pioneers the use of Anodized Aluminum Mitad, enhancing heat transfer efficiency and ensuring precise baking conditions. Additionally, the adoption of a Parabolic trough collector enables highly efficient energy capture, surpassing the Parabolic dish used in Ref. [8]. Moreover, the choice of Shell heat transfer fluid oil S2 as the working fluid ensures reliable and controlled heat transfer, outperforming the use of steam in Ref. [8] and electric current in Ref. [7]. The utilization of forced circulation with an oil pump for heat transfer distinguishes this research, offering superior efficiency compared to the natural circulation boiling-condensation method employed by Ref. [8]. Notably, this study achieves shorter heat-up and baking times, indicative of its enhanced efficiency when compared to Refs. [7,8]. Furthermore, by achieving a lower optimal baking temperature range, this research promises significant energy savings and improved cooking quality compared to its counterparts. Lastly, the emphasis on indoor baking in this study contrasts with the outdoor baking focus of [8]. These key differences Reinforce the groundbreaking advancements and practical implications of this research in the domain of solar-powered Injera baking technology.

6 Conclusion

In summary, the development of a novel solar thermal system for Injera baking marks a significant step towards sustainable energy utilization in culinary practices. Through meticulous design and analysis, this study has culminated in the integration of three core elements: a solar collector section, thermal storage components, and a dedicated baking unit.

The design intricacies, including the utilization of Anodized aluminum plate for the Mitad and strategic implementation of oil galleries for heat distribution, Accent a commitment to efficiency and functionality. Notably, the system's capacity for baking 11,000 Injera per day, catering to the dietary needs of 5500 students over 6 h, showcases its practicality and relevance in real-world settings.

Moreover, computational simulations have elucidated the system's thermal performance and heat flux dynamics, revealing promising results in terms of uniform temperature distribution and enhanced energy absorption. These findings not only validate the efficacy of the solar thermal approach but also hint at its potential for scalability and widespread adoption.

Looking ahead, the quest for continuous improvement remains imperative. Future research endeavors will focus on refining material selection for the baking pan, with an emphasis on enhancing thermal conductivity. Additionally, efforts to minimize heat losses and optimize system efficiency will be pivotal in ensuring sustained progress and viability in solar thermal Injera baking technology.

Ultimately, this study Underlines the transformative potential of renewable energy solutions in traditional culinary practices, offering a compelling pathway towards energy sustainability, cost efficiency, and environmental stewardship.

Data availability statement

The data used to support the findings of this study are available from the corresponding author upon request.

CRediT authorship contribution statement

Habtamu Terefe Retta: Writing – original draft, Writing – review & editing, Validation, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization, Visualization. Mesele Hayelom Hailu: Supervision, Conceptualization. Aklilu Tesfamichael Baheta: Visualization, Supervision, Conceptualization. Misrak Girma Haile: Methodology, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A Table 1 Bill of materials for solar energy based Injera baking system

Table 1Number	Name	Quantity	
1	Parabolic trough collector with 1.71m focal length, 5.76m aperture width and 532.9 m2 aperture area	8	
2	Receiver (heat exchanger)	1	
3	Ball valve 1, ∅100mm	1	
4	Ball valve 2, ∅100mm	1	
5	KCB oil transfer gear pump	1	
6	Oval gear variable flow meter	1	
7	Ball valve 3, ∅100mm	1	
8	Ball valve 4, ∅100mm	1	
9	Hot oil storage tank	1	
10	Ball valve 5, ∅100mm	1	
11	KCB oil transfer gear pump	1	
12	Oval gear variable flow meter	1	
13	Ball valve 6, ∅100mm	1	
14	Mitads, with heating capacity of 2.11 kW and geometric dimension of 0.56m diameter, 0.01m thickness, made of aluminum.	92	
15	Ball valve 7, ∅8mm	1	
16	Oil distributor pipeline	1	
17	Cold oil storage tank	1	
18	Ball valve 8, ∅100mm	1	
19	Return pipeline 1	1	
20	Return pipeline 2	1	
21	Return pipeline 3	1	
22	Supply pipeline 2	1	
23	Supply pipeline 1	1	

Fig. 13 3D model of the solar energy based Injera baking system.

Fig. 13

Acknowledgements

The authors would like to express their gratitude to the Department of Mechanical Engineering at Mekelle University in Mekelle, Ethiopia, for their immense support in helping to achieve the objectives of this work.
==== Refs
References

1 Yayeh M. Thermal Storage Device for Indoor Injera Baking Apr. 2013 1 91
2 Hassen A.A. Kebede S.B. Wihib N.M. Design and manufacturing of thermal energy based injera baking glass Pan Energy Proc. 93 Aug. 2016 154 159 10.1016/j.egypro.2016.07.164
3 Hailu M.H. Nydal O.J. Kahsay M.B. Tesfay A.H. A direct solar fryer for injera baking application ISES Solar World Congress 2017 - IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2017, Proceedings 2017 International Solar Energy Society 1475 1485 10.18086/swc.2017.24.02
4 Negash S.M. Omiogbemi I.M.B. Dagwa I.M. Development of a partially automated electric injera baking stove with improved efficiency and production rate AIP Conf. Proc. 2341 May 2021 10.1063/5.0049946
5 Nega D.T. Mulugeta B. Demissie S.W. Improved biogas ‘Injera’ bakery stove design, assemble and its baking pan floor temperature distribution test Energy Sustain. Dev. 61 January 2021 65 73 10.1016/j.esd.2020.12.009
6 Tadesse M. The developmental patterns of injera baking stoves: review on the efficiency, and energy consumption in Ethiopia Int. J. Mech. Eng. 7 1 2020 7 16 10.14445/23488360/ijme-v7i1p102
7 Hassen A.A. Amibe D.A. Nydal O.J. Performance investigation of solar powered injera baking oven for indoor cooking 30th ISES Solar World Congress Proceedings July 2011 Kassel, Germany
8 Tesfay A.H. Kahsay M.B. Nydal O.J. Design and development of solar thermal Injera baking: steam based direct baking Energy Procedia 2014 Elsevier Ltd 2946 2955 10.1016/j.egypro.2014.10.330
9 Goytom D. Finite difference modelling of solar thermal powered injera baking oven Int. Adv. Res. J. Sci. Eng. Technol. ISO 3297 2007 10.17148/IARJSET.2016.31223
10 Tesfay A.H. Asfafaw Haileselassie Tesfay Experimental Investigation of a Concentrating Solar Fryer with Heat Storage (Electronic Version) 2015 Norwegian University of Science and Technology Norwegian
11 Hailu M.H. Kahsay M.B. Tesfay A.H. Dawud O.I. Energy consumption performance analysis of electrical mitad at Mekelle City Momona Ethiop. J. Sci. 9 1 Jun. 2017 43 10.4314/mejs.v9i1.4
12 Wielage B. Alisch G. Lampke T. Nickel D. Anodizing - a key for surface treatment of aluminium Key Eng. Mater. 384 2008 263 281 10.4028/www.scientific.net/kem.384.263
13 Yohaness E. Design Manufacturing and Testing of Scheffler Reflector for the Extraction of Essential Oil: Case of Eucalyptus- Globules 2013 Mekelle University Mekelle
14 Chung M.H. Estimating solar insolation and power generation of photovoltaic systems using previous day weather data Adv. Civ. Eng. 2020 2020 10.1155/2020/8701368
15 POWER | data access viewer [Online]. Available https://power.larc.nasa.gov/data-access-viewer/
16 Reyad S. Steps for Design of Heat Exchanger 2015 King Fahd University of Petroleum & Minerals
17 Fanta F. Improving performance of electromagnetic induction injera mitad Int. Res. J. Eng. Technol. 7 4 Apr. 2020 1 5 [Online]. Available www.irjet.net
18 Mishra S. Tripathy P. Solar thermal electricity generating system Int. J. Adv. Res. Technol. 1 2012
19 Kumar Satish Chand Umrao A.O. Design and analysis for 1MWe Parabolic Trough solar collector plant based on DSG method IJERT) 2 6 Jun. 2013 1 15 [Online]. Available www.ijert.org
20 Abdelfatah R.T. Fahim I.S. Kasem M.M. Investigative Review of Design Techniques of Parabolic Trough Solar Collectors 2024 10.32604/fhmt.2023.044706
21 Patel H.R. Chaudhari A.R. Patel V.B. A Comprehensive Review on Design Aspects and Performance Characteristics of Solar Parabolic Trough Collector September, 2022 10.20508/ijrer.v12i3.12999.g8541
22 Kearney D. Assessment of a molten salt heat transfer fluid in a parabolic trough solar field J. Sol. Energy Eng. Trans. ASME 125 2 May 2003 170 176 10.1115/1.1565087
23 Geyer M. EUROTROUGH-parabolic Trough Collector Developed for Cost Efficient Solar Power Generation 2002 Switzerland
24 Fredriksson Chaves J.R. Giese L. Herzog M. Concentrating Solar Power: a comparison and evaluation of innovative parabolic trough collector concepts for large scale application and Natural Sciences, Master thesis 2019 Technical University of Applied Sciences Wildau Faculty of Engineering B8 B9
25 Yohanes Modeling And Experimental Testing Of Solar Powered Injera Baking 2020 Bahir Dar university Bahir Dar [Online]. Available http://ir.bdu.edu.et/handle/123456789/12815
26 Jones R. Diehl J.C. Simons L. Verwaal M. The development of an energy efficient electric Mitad for baking injeras in Ethiopia Proceedings of the 25th Conference on the Domestic Use of Energy, DUE 2017 May 2017 Institute of Electrical and Electronics Engineers Inc 75 82 10.23919/DUE.2017.7931827
27 Liyew K.W. Louvet Y. Habtu N.G. Jordan U. A techno-economic analysis of solar injera baking systems Proc. - ISES Sol. World Congr January 2021 825 830 10.18086/swc.2021.31.04 2021
