Fabrication and Experimental Study of a Solar Cooker with Electrical

J. Energy Power Sources
Vol. 1, No. 4, 2014, pp. 225-231
Received: July 30, 2014, Published: October 30, 2014
Journal of Energy
and Power Sources
www.ethanpublishing.com
Fabrication and Experimental Study of a Solar Cooker
with Electrical Back-Up
Poonam Rajawat1, 2, Sunita Mahavar1 and Prabha Dashora1
1. Department of Physics, University of Rajasthan, Jaipur, Rajasthan 302004, India
2. Govt. Polytechnic College, Tonk, Rajasthan 304001, India
Corresponding author: Poonam Rajawat ([email protected])
Abstract: This paper presents fabrication and experimental study of a SCEB (Solar Cooker with Electrical Back-Up). In this system
electrical back-up is provided with four mica sandwich strip heater (each 90 W). A thermostat is attached at the outer side of the system
through which temperature of the absorber plate can be controlled in the range 50 °C to 150 °C. To analyze the effect of electrical
back-up experiential studies have been carried out under different conditions. These are: (1) without back-up, without load; (2) without
back-up, with load; (3) with back-up, with load. It has been found that for single meal cooking the consumption of electricity is 0.38
unit under indoor experiment, while it is less than half of it (0.18 unit) for outdoor test. Two figures of merit (F1 & F2) for solar cookers
have also been calculated and their values are found to be 0.12 °C m2/W and 0.462, respectively. Different temperature profiles and
cooking times of different food items are presented in the paper. Net present value and payback period are also calculated and included.
The developed cooker is suitable for two meals cooking even during the cloudy days with low electricity consumption.
Key words: Solar cooker, electrical back-up, strip heater.
1. Introduction
Extensive fossil fuel consumption in almost all
human activities led to some undesirable phenomena
such as atmospheric and environmental pollutions,
which are increasing drastically [1-2]. To avoid these
problems there are two constructive alternatives either
to improve fossil fuel quality with reductions in their
harmful emissions into the atmosphere or replace fossil
fuel usage as much as possible with environmental
friendly, clean and renewable energy sources. Among
these sources, solar energy is a promising option due to
its abundance and more evenly distribution in nature
than any other renewable energy types such as wind,
geothermal, hydro, wave and tidal energies.
In current domestic energy scenario the mass
population of underdeveloped and developing nation is
on the horns of a dilemma of unaffordability; due to
tremendous price hike; of clean cooking fuel and
unavailability of fuel wood due to rapid deforestation.
So, the maximum utilization of available solar energy
for cooking may prove to be a boon for low income
mass population of the world.
The existing solar cookers cannot be used
satisfactorily during cloudy or rainy days or during off
sunshine hours. A back-up system can overcome these
limitations of the existing systems. A number of solar
cookers have been developed without any back-up [3-8]
and few research papers are found on back-up [9]. This
paper presents fabrication and experimental study of a
SCEB (Solar Cooker with Electrical Back-Up).
Temperature profiles of different components during
different experiments, cooking time of various food
items, NPV (Net Present Value) and payback period of
the developed cooker are presented in this paper. Two
figures of merit (F1 & F2) recommended by bureau of
Indian standards (BIS 1992) for solar cookers have also
been calculated and their values are found to be 0.12 °C
m2/w and 0.462, respectively. Low electricity
226
Fabrication and Experimental Study of a Solar Cooker with Electrical Back-Up
consumption in cooking during cloudy days and safe
handling are important features of the cooker.
2. Fabrication of the System (SCEB (Solar
Cooker with Electrical Backup))
From last fifteen years our research group is working
on the design, development and study of light weight,
low cost portable solar cookers [10-11], building
material, fixed structure solar cookers [12-13] and
small size solar cookers [14-17]. Recently, a solar
cooker has been developed with electrical backup
(SCEB) and presented here.
The outer dimensions of the system are 59 × 59 × 23
cm3. The system has fiber casing. A trapezoidal
aluminum tray (thickness 0.45 mm) of dimension 41 ×
41 cm2 at the base and 50 × 50 cm2 on the aperture with
Fig. 1 Photograph of solar cooker with electrical backup.
the height 9 cm is used as absorber. This is painted with
black matt paint. Ceramic fiber is used as insulation
material (thickness of 5 cm) at the bottom and sides. It
is a good electrical insulator as required in electrical
appliances. Double glaze of transparent toughened
glass of thickness 5 mm with air gap of 13 mm is used.
A plane glass mirror of thickness 4mm and dimensions
50 × 50 cm2, hinged at the top of the cooker is used as
reflector. To adjust mirror angles holes are provided on
both outer sides of the cooker. Four wheels are used in
the bottom to increase the ease in movement of the
cooker. Four containers of diameter 18 cm and height 6
cm, which are appropriate for cooking requirement of
four to six people, are used during experiments.
Electrical backup arrangement: The electrical
backup is provided with four mica sandwich strip
heaters (each 90 W) which are in circular disc shape.
Fig. 2
These are fixed at the back surface of the absorber tray
schematic diagram is shown in Fig. 2. The costs of the
various components of SCEB are given in the Table 1.
and are connected in series. Temperature of the
absorber plate is controlled by a thermostat provided at
the outer side; this is attached at one outer side of the
cooker. The temperature of absorber plate can be fixed
(between 50 °C to 150 °C) as per the requirement of the
food item.
Photograph of SCEB is given below (Fig. 1) and the
Schematic diagram of SCEB.
3. Thermal Performance Parameters
For the evaluation of thermal performance of a solar
cooker two parameters (first figure of merit (F1) &
second figure of merit (F2)) are recommended by
Bureau of Indian standard (BIS). F1 and F2 are calculated
Fabrication and Experimental Study of a Solar Cooker with Electrical Back-Up
Table 1
227
Costs of various components of SCEB.
S. No.
Component
Quantity
2
Rate INR/m2
Approx. Cost (INR)
1.
Glaze
0.25 m
1185
296
2.
Absorber tray
0.36 m2
270
97
3.
Insulation
1.8 m2
215
387
2
4.
Reflector
0.28 m
485
135
5.
Fiber body Casing
1.26 m2
484
610
(1) Four strip heaters
4
-
800
(2) Thermostat cost
1
-
250
(3) Assembling cost
-
-
250
Backup arrangement
6
7.
Screws and other accessories
200
8.
Manufacturing cost
1000
Total cost
4025
by stagnation test and sensible heat test, respectively
[18-19].
The first figure of merit (F1) of a box-type solar
cooker is defined as the ration of optical efficiency (η0)
to the overall heat loss coefficient (ULS) and is given as
[18-19]:
η
(Tps − Tas)
F1 = 0 =
ULS
Is
where Tps, Tas and Is are the plate temperature, ambient
temperature and solar insolation on the horizontal
surface, respectively, at stagnation.
The second figure of merit (F2) of a box type solar
cooker can be obtained using the following relation
[18-19]:

1  Tw1 − Ta  

 1 − 
F 1  Is  
F 1 (MC)w 
F2 =
In

Ap τ
1  T w 2 − Ta  
 
1 − 
 F 1  Is  
where (MC)w is the product of mass of water and its
specific heat capacity, Ap is the aperture area of the
cooker, τ is the time interval in which water
Ta is the average
temperature rises from Tw1 to Tw2. തതത
ഥ
ambient temperature and Is is the average solar
radiation for the duration τ. To determine F2, the
values of Tw1 to Tw2 are selected between initial linear
rise of water temperature from the experimental curve
as suggested by Mullick at el. [19].
4. Experimental Study
All the experiments have been done at the
University of Rajasthan, Jaipur. In indoor experiments
the electricity consumption has been measured by the
electric meter. During outdoor experiments, the solar
radiation intensity on a horizontal surface has been
measured using a pyranometer (Nation Instruments
Ltd. Calcutta, instrument no. 0068) for the
experimental location (26.92 ºN, 75.87 ºE). The
ambient temperature is measured using a thermometer
(accuracy 0.1 ºC) placed in an ambient chamber and
wind speed for outdoor experiments is measured by an
aerometer (Prove instruments inc. AVM-03). In all the
experiments CIE-305 thermometer with point contact
thermocouples has been used to measure the
temperatures at different locations of the cooker; viz.
the cooking fluid, the absorber plate, the lower and
upper glass covers.
(1) Without back-up and without load: Under this
condition only outdoor experiments have been
performed to determine first figure of merit (F1). The
measured temperatures of different components of the
system for one representative day are shown in Fig. 3.
(2) Without back-up and with load: Outdoor
experiments have been performed without back-up and
with full load (2.0 kg water), which is calculated for
the aperture area of SCEB as per Mullick at el. [19].
The thermal profile of one representative day is shown
in Fig. 4. Second figure of merit (F2) is calculated from
228
Fabrication and Experimental Study of a Solar Cooker with Electrical Back-Up
Fig. 3 Variation of the bare plate temperature (Tp),
ambient temperature (Ta), upper glaze temperature (Tgu),
lower glaze temperature (Tgl) and insolation with standard
time on 15/10/2012(without reflector).
Fig. 4 Temperature profile of the different components
(Tp-plate, Tw-water load, Tgu-upper glaze and Tgl-lower
glaze temperature) of SCEB and variation of Is with the
standard time (without reflector and with 2.0 kg water load
on 05/04/2012).
this thermal profile.
(3) With back-up and with load: As SCEB is
developed for indoor cooking and cooking during
sunny as well as cloudy days. So, to analyze the effect
of electrical back-up both indoor and outdoor thermal
performances have been measured with full load (2.0
kg water) with backup. In both tests the maximum
temperature was set at 130 °C from the back-up
arrangement. As the plate temperature reaches more than
Fig. 5 Temperature profile of the different components
(Tp-plate, Tw-water load, Tgu-upper glaze and Tgl-lower
glaze temperature) of SCEB with time in hour (indoor with
backup and with 2.0 kg water load).
Fig. 6 Temperature profile of the different components
(Tp-plate, Tw-water load, Tgu-upper glaze temperature) of
SCEB with time in hour 19/10/2012 (outdoor, with backup
and with 2.0 kg water load).
this temperature, the backup automatically cut downs
and starts again if it goes below 10 °C from 130°C. The
indoor and outdoor thermal profiles are shown in Figs.
5-6, respectively.
5. Cooking Exercises of SCEB
Along with the thermal performance measurements,
cooking exercises have also been done in SCEB. The
Fabrication and Experimental Study of a Solar Cooker with Electrical Back-Up
Table 2
229
Different food items cooked in SCEB.
S. No.
Date
Starting Time
Name of Dish
Ingredients
Cooking time
1.
26 April 2013
10.45
Kheer Cooking
1 L milk + 100 g rice + 50 g dry fruits & sugar
3h
2.
29 April 2013
10.15
Maggie
100 g Maggie + 240 g water + 150 g vegetables
1 h 10 min
3.
01 May 2013
10.40 AM
Rice cooking
600 g rice + 1200 g water + 600 g vegetables
2 h 20 min
4.
03 May 2013
10.30
Suji roasting
3h
5.
04 May 2013
11.30
Khaman Dhokla
1 kg (equally spread in four containers)
250 g Khaman mix + 300 mL water + 800 g
water for steam making
cooking exercises are performed without back-up, with
reflector and these are given in Table 2.
6. Energy saving and Economic Analysis of
SCEB
The payback period and the NPV (Net Present Value)
for SCEB have been computed by using the following
relations, respectively [20-22]:
(E − M )
− C]
( a − b)
log[(1 + a )/(1 + b)]
log[( E − M ) /( a − b)] − log[
N=
NPV =
n
( E − M )   (1 + b  
1 − 
  −C
(a − b)   1 + a  
where C is the cost of the system (that is 4025 INR for
SCEB), E is the energy-saving price for commonly
used fuels such as firewood, cowdung, coal, kerosene,
electricity and LPG. M is the maintenance cost of the
system per year which increases at the rate of b every
year, inflation in fuel price is assumed same to the rate
of increasing maintains cost. i.e., b, a is the compound
annual interest, n is the number of year.
Energy consumption for cooking in developing
countries is a major component of the total energy
consumption
including
commercial
and
non-commercial energy source. Most parts of India
receive 4-7 kWh of solar radiation per m2 per day with
more than 280 sunny days in a year. As the energy for
cooking per person is about 900 kJ of fuel equivalent
per meal [21]. So the developed cooker could save
252 MJ energy/year/person/meal. This cooker can
save 2016 MJ energy per year (for four persons)
which is a considerable amount of energy. By taking
this energy saving quantity the payback periods and
net present values have been calculated for SCEB with
1 h 30 min
respect to other cooking fuels. The NPVs and payback
periods have been calculated at the following rates a =
10 %, b = 8 % and M = 10 % of the cost of the cooker;
and presented in Table 3.
7. Results and Discussion
The temperature profiles of various components of
SCEB, under different test conditions, are depicted in
Figs. 3-6. During stagnation test as shown in Fig. 3, the
bare plate temperature stagnated at about 125 °C
around 12:40 IST. The highest temperature attained by
the bare plate was 126.5 °C ( Iഥs = 765 W/m2, Tഥa =
33.4 °C). At stagnation upper and lower glaze
temperature remained around 50 and 92 °C,
respectively. The first figure of merit (F1) is found to
be 0.12 °C m2/W and this value is acceptable as per
BIS [18] and Mullick et al. [19].
Fig. 4 shows that, with the full water load (2.0 kg)
the water temperature reached 80 °C in 1:40h. The
value of second figure of merit (F2) calculated from this
thermal profile is found to be 0.462 (using Iഥs = 805
W/m2, Tഥa = 36 °C, Tw1 = 60.7 °C and Tw2 = 91.2 °C).
Fig. 5 shows in the developed solar cooker a soft
meal can be cooked as the water temperature reaches
to 90 °C and sustain this temperature till 20 mints. For
one meal cooking the consumption of electricity is
noted to be 0.38 units from indoor experiment (Fig. 5)
while this consumption is less then the half 0.18 units
for outdoor test (Fig. 6). It is clear from the figures
that the temperature reached 80 °C in 50 min in indoor
condition (Fig. 5) while in outdoor with back-up test it
reached 80 °C in 30 min only (Fig. 6).
Table 2 shows that solar cookers are suitable for
boiling, baking and steaming cooking exercises. The
Fabrication and Experimental Study of a Solar Cooker with Electrical Back-Up
230
Table 3
NPV and payback period of SCEB.
Net Present value in (INR)
Type of fuel
Calorific value
(MJ/kg)
Efficiency
Cost (INR)
Energy Saving
(INR)
n=5
n=10
Firewood
17
0.1
7.7/kg
9783.5
37093.4
74607.2
0.47
Cowdung
9
0.11
2.5/kg
5454.5
18118.8
38321.5
0.88
Payback
period (Year)
Coal
28
0.28
15/kg
6887.8
12324.8
27241.3
1.19
kerosene
38
0.48
25/L
1776.3
7187.2
17416.5
1.74
electricity
3.6
0.76
5.42/kWh
4278.9
12966
28467.6
1.14
LPG
45.5
0.6
28.9/kg
2286.6
4233.3
11767.6
2.38
payback period of SCEB varies from 0.47 to 2.38 years
and NPV varies 11767 to 74607 INR, according to the
fuel type (Table 3). The payback period of SCEB is
reasonably small to be accepted by mass population.
[9]
[10]
8. Conclusions
The current investigation introduced the design,
construction and the test results of a SCEB to reduce
the cooking times and also saves a significant amount
of conventional energy. It is a user friendly solar
cooker which is easy to repair by the users themselves.
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