Available online at www.sciencedirect.

com

ScienceDirect
Energy Procedia 93 (2016) 154 – 159

Africa-EU Renewable Energy Research and Innovation Symposium, RERIS 2016, 8-10 March
2016, Tlemcen, Algeria

Design and manufacturing of thermal energy based Injera baking

Abstract

The current practice of Injera (Spongy flat bread) baking is based on energy sources such as fire wood and fossil fuels, which are
both the main causes for environmental pollution and depletion of forest resources. The aim of this research is to propose a new
type of baking system where solar thermal energy is used as a power source. The possibility of baking on a glass stove is
investigated using solar thermal energy transferred to the kitchen by means of a circulating heat transfer fluid heated by solar
energy concentrated by a parabolic trough. The existing three stone biomass based clay baking pan results in a loss of a major
portion of the supplied energy and the baking process also results in significant amounts of indoor air pollution. The proposed
system is solely based on a renewable energy source such as solar energy. For experimental simplicity and investigation of the
possibility of baking on glass stove, the heat transfer fluid is heated by simulating the solar energy with electricity, and the heated
fluid is allowed to circulate through the closed loop of the baking pan assembly. Surface temperatures of 191 °C were achieved
on top of the glass baking pan and Injera baking experiments were performed successfully.

© 2016
© 2016 The
TheAuthors.
Authors.Published
Publishedby by
Elsevier Ltd.Ltd.
Elsevier This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of RERIS 2016.
Peer-review under responsibility of the organizing committee of RERIS 2016
Keywords: Solar energy; Injera baking; glass pan.

* Corresponding author. Tel.: +251 911 811 528; fax +251 582 26 62 46.
E-mail address: abdiaman2004@yahoo.com

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of RERIS 2016
doi:10.1016/j.egypro.2016.07.164
 Abdulkadir A. Hassen et al. / Energy Procedia 93 (2016) 154 – 159 155


Introduction

The availability of adequate energy for household cooking is one of the most important concerns of people in
Ethiopia. Ethiopians’ high dependence on biomass energy resources contribute to deforestation, soil erosion, and
land degradation. The conventional energy sources are limited and rapidly becoming depleted with time; on the
other hand, rapid population growth and expanding human activities are exerting extra pressure with additional
demand on the shrinking amount of energy resources.
Ethiopia is the third largest user of traditional fuels for household energy use in the world; with 96 % of the
population dependent on traditional biomass (e.g., fuel wood and dung) to meet household energy demand. This is
in comparison to 90% for Sub-Saharan Africa and approximately 60% for the African continent [1].
Injera is spongy flat bread with a distinctive taste and texture. It is predominantly eaten as a staple food item in
Ethiopia and some parts of East Africa. It is similar to an Indian chapatti but with small bubbly structures on top.
Injera baking requires temperatures ranging from 180 °C – 220 °C [2]. In most households of Ethiopia, the energy
demand for baking Injera is largely met with bio-fuels such as fuel wood, agricultural residue and dung cakes,
whereas electricity is used in some of the urban households. In most households, this Injera baking system is carried
out using an open fire / three stone / baking system which are inefficient and wasteful techniques. One serious
disadvantage of this method is that it consumes considerable quantities of firewood, estimated to be at least 50 % of
the biomass energy consumption per household per year [3]. To improve health and general welfare, better cooking
and heating facilities are important. Solar cooking can decrease the health hazards associated with indoor fire
cooking and the economic burdens associated with fire-wood gathering or purchase [4].
While many designs exist for improving the existing Injera baking systems, relatively few exist for baking using
a renewable energy source. The existing proposed systems are also limited to direct cooking technologies by
illuminating the pots on the sides as well as the bottom. Whereas, for Injera baking, the heating must be directed to
the bottom of the baking pan and cultural habits also require the baking process to be done under indoor conditions.
The solar fryer which is specifically designed for cooking Injera was developed by Gallagher [4]. He used a 0.46
m diameter pan and 1.2 m diameter mirror for his prototype, which was designed for cooking 0.42 m diameter slices
of Injera. A mirror below the pan directs the radiation to the pan bottom, which is coated with a low-emissivity
black absorber. The mirror uses flat, hexagonal panels of aluminised-Mylar to provide uniform illumination across
most of the pan bottom. This system is mainly designed for cooking outdoors.
The other well-known solar fryer was developed by Devos [5] by arranging an array of 0.15 m square glass
mirrors in a 1.54 m2 rectangle, with each mirror tilted to fit an off-axis parabola. The array is placed near the ground
just beyond a table that supports the fry pan, which sits at an opening in the table. Reflected sunlight is brought to a
quasi-focus on the bottom of the pan, and a metal vane below the table is used to block part or all of the incident
sunlight. The mirror angle is adjusted through the day and the seasons to direct focused sunlight to the pan.
Prassana and Unanand [6] proposed a hybrid solar cooking system where the solar energy is transported to the
kitchen by means of circulating fluid. They proposed an option to maximize the sun energy by changing the flow
rate of the circulating fluid dynamically.
The main objective of this work is to design and manufacture a laboratory prototype for an oil based Injera
baking glass stove system and analysing its performance experimentally. The working fluid is heated using
parabolic trough and discharges the heat to the specially designed glass baking pan. In conventional Injera baking,
there is a smoke emission from domestic fuels which is the major source of indoor pollution, especially in rural and
poor urban communities. This smoke contains pollutants and particulates that adversely affect the health of
inhabitants. The proposed system is free of smoke, hence, improves the health and safety of the user. A solar
powered Injera baking technology is expected to contribute considerably towards meeting domestic cooking energy
requirement in a country blessed with abundant sunshine. Besides, the proposed glass baking pan results in shorter
heat-up time and savings in energy compared to the existing clay baking pan.


156 Abdulkadir A. Hassen et al. / Energy Procedia 93 (2016) 154 – 159

Fig. 1. Main components of the laboratory prototype.

2.
Methods and Material

The laboratory model of the proposed solar powered Injera baking system is shown in Fig. 1. The main materials
that are required for the work are a tempered glass plate, sheet metal, storage tank, pipe, elbows, Gasket maker,
angle iron, aluminium sheet, bolt and nut, Shell Thermia oil B, gear pump, motor, control valves and welding rod.
The materials selection is based on local availability and cost affordability.
Due to the difficulty of getting a small size high temperature resistant pump for this type of application, an effort
has been made to use a chain drive gear type oil pump from used track engine, by modifying the input shaft to fit
with the required flow velocity of the oil.

The Shell Thermia oil B was used as a heating medium as the Injera baking process requires very high surface
temperature usually in the range of 180 °C to 220 °C . In order to simulate the solar heat energy, an electrical heating
element is used to raise the temperature of the working heat transfer fluid in the storage tank until the required
baking surface temperature is achieved during pumping. Thus, heat is transferred from the heated oil to the baking
glass by convection and to Injera by conduction heat transfer mechanisms.
To transfer heat energy uniformly from the heat transfer oil and to overcome sudden drop of surface temperature
during baking through application of the batter below the optimum baking temperature, an oil reservoir below the
pan was used. The oil inlet and outlet ports were drilled with 1/2-inch (0.0127 m) diameter size on opposite sides of
the housing of the gallery; pipes sockets with 1/2-inch diameter were welded to the drilled inlet and outlet ports. Fin
like structures were welded inside the oil gallery to hinder direct oil flow and thus increase the contact time between
heat transfer oil with the pan supporting plate and also to increase strength of the gallery. In order to decrease heat
loss, the oil gallery was insulated by an ash insulation system which has about 3.5 cm thickness from below and the
side wall. The Injera baking pan assembly is placed in the kitchen where the baking is done. All other components
are placed at intermediate levels (outdoor or within the kitchen) according to the building requirements.

3.
Results and discussion

The experiment was conducted in the Mechanical Engineering laboratories of Bahir Dar Institute of Technology.
Different tests were performed to observe the performance of the system during initial heat up and baking. K-Type
thermocouples were used to record the temperature variations in the heating and storage tank, baking pan inlet,
baking pan outlet and on the surface of the baking pan. Injera baking experiments were also conducted successfully
and the results of the experiment will be presented and discussed below.
 Abdulkadir A. Hassen et al. / Energy Procedia 93 (2016) 154 – 159 157

Fig. 2. Profile of heating oil and baking glass pan temperatures

3.1.
Heat up Time and Temperature distribution of oil in the heating and storage tank

The oil in the storage tank was heated using a 2 kW electrical heater; the temperature increased gradually but the
increasing rate was higher during initial heat-up time. Figure 2 shows the temperature variation during initial heating
of the oil in the storage tank and heating-up of the baking pan. The maximum oil temperature is about 300 °C and
pumping was started at this temperature. The oil temperature at the outlet from the baking pan assembly was lower
than the oil temperature at the inlet to the baking pan assembly; this was mainly due to some energy (temperature)
loss to heat up the glass surface. When pumping was started, the temperature of the oil in the oil tank dropped from
300 °C to about 240 °C.

In addition to the loss in piping lines, the temperature of the oil in the oil gallery was at room temperature; and
during pumping the cold oil in the gallery was mixed with the hot oil in the tank and makes the temperature to drop
to 240 °C. This is a starting heat loss and the temperature drop will reduce during subsequent baking cycles. The
temperature recovery during the baking session is also presented in Figure 3.

3.2.
Baking of Injera on the prototype

The baking of Injera starts after the baking pan surface temperature reached 191 °C. When the batter (locally
called ‘lit’) was poured onto the pan surface, the temperature of the pan surface dropped to about 92 °C. From a
series of experiments, an average of two minutes to bake one Injera and about two minutes to recover the pan
surface temperature to the baking temperature were recorded, i.e. each Injera baking cycle took about four minutes.
Figure 3 shows the heat-up time for oil in the tank and baking pan surface, with temperature profiles during five
Injera baking session.
158 Abdulkadir A. Hassen et al. / Energy Procedia 93 (2016) 154 – 159

Fig. 3. Profile of heating oil and baking glass pan temperatures variation during heat-up and baking session.

The oil below the baking pan allows for the maintaining of the surface temperature for subsequent baking
activities and the high thermal conductivity of the glass baking pan is a plus for quick recovery of the surface
temperature after each baking session. Figure 4 shows the laboratory model setup and Injera baked on the pan
surface of the laboratory prototype after two minutes of heating.

4.
Conclusion

To reduce the dependence on fossil fuels and their adverse environmental effects when burnt, a renewable energy
based Injera baking system is proposed as an alternative. This study demonstrated the possibility of baking Injera
using an indirect thermal energy source in a high temperature heat transfer fluid. For experimental purposes, the
solar energy source is simulated by an electric heating element, where the electrical energy required is determined
by calculating the useful heat energy obtained from a solar parabolic trough based system.

Fig. 4. Laboratory model components (a) and Injera baked on the prototype (b).

 Abdulkadir A. Hassen et al. / Energy Procedia 93 (2016) 154 – 159 159

The possibility of baking on a new type of energy saving baking pan, i.e., glass baking pan was also
demonstrated by successful baking of Injera using the proposed prototype. The working heat transfer fluid (Shell
Thermia B) has the advantage of maintaining the temperature for longer periods (estimated 3 to 4 hours) after the
power source is off and this is an additional advantage during fluctuations in sunshine periods.
In general, this study demonstrates the possibility of baking Injera on a glass pan using solar thermal energy
source (solar energy simulated by equivalent electrical energy). The cultural barriers related to the use of this new
system can be mitigated through time by creation of awareness and demonstrating the economic and environmental
benefits from the use of the product. This study is extended from the previous research collaboration between five
African universities from Uganda, Ethiopia, Mozambique and Norwegian University of Science and Technology
(NTNU) on small scale solar concentrating system and its realization can be incorporated in future research
collaboration between African and EU partners.

References

[1] Jargstorf B. Renewable Energy and Development. In: Deutsche Gesellschaft für Technische Zusammenarbeit & Ethiopian Rural Energy
Development and Promotion Centre.Addis Ababa:Ethiopia; 2004
[2] Abdulkadir A H, Demiss A A, Ole J N. Performance investigation of solar powered Injera baking oven for indoor cooking. ISES solar world
congress proceedings, Kassel, Germany; 2011, p. 186-196
[3] Araya A, Yissehak D. Sustainable Household Energy for Addis Ababa Ethiopia. Consilience: The Journal of Sustainable Development;
2012. 8(1): p. 1-11.
[4] Alan G. A solar fryer. Science direct, Solar energy 85; 2011, p. 496–505
[5] Devos,Xavier,2006, A Paper presented at the 2006 Granada solar cooking Conference, June 2010,
http://solarcooking.wikia.com/wiki/Devos_cooker
[6] Prasanna, U.R.,L. Umanand. Optimization and design of energy transport system for solar cooking application. Applied Energy; 2011. 88(1):
p. 242-251.