V o l u m e
Abstract
The considerations on how
the oven chamber, the aperture area and the mirror
reflector area of solar box
cooker were designed are
described. A model of evaluation, which uses the oven
temperature information
has been derived, so that the
cooker performance can be
derived without involving
the uncertainty about the
1
-
M a y
2 0 0 5
( 6 9 - 7 5 )
Sun Cooking is the Best
Practice in Indonesia
Herliyani Suharta*, A.M. Sayigh**
and S.H. Nasser **
*Technical Implementation Unit Energy
Technology Laboratory (UPT LSDE) - BPPT,
PUSPIPTEK, Serpong, Tangerang 15314,
Indonesia.
E-mail: herli@iptek.net.id
** University of Hertfordshire, ACME, Hatfield
Herts, AL10 9AB, United Kingdom
1. Introduction
heat capacity of the cooker
interiors. It is also used to
conform the effect of design
change on the performance.
This paper reviews a
concept in design technology that is combined with a
dissemination mechanism
through a community education and the societal background why sun cooking is
needed. A preliminary test of
concentrator cooker K10 is
briefly described.
3) Glass has good transmittance (τ) and can stand to long
exposure of UV radiation and heat and also locally available. Dietz (1954) found that glass becomes substantially
opaque at wavelength longer than approximately 3 µm and
is considered opaque for long-wave radiation. Duffie and
Beckman (1980, p174) show the solar transmittance of
1,2,3 and 4 glass layers is about constant for solar incidence angle between 0° until about 45°, which means between 9:00 am until 3:00pm on equatorial belt. Three
layers of ordinary glass, therefore, are used as transparent
insulator at the upper part. More than three layers will
increase the weight and the price of solar cooker.
Indonesia islands are scattered in the equatorial belt. Annual
journey of the earth leads to four important positions of the
sun, those are : - spring equinox where sun perpendicular to
equator on 21 March, - summer solstice on 22 June (the sun
declination angle is +23.5°), - fall equinox on 21 September
and - winter solstice on 22 December (the sun declination
angle is –23.5°). On equator, these sun positions give a little
different on daily sunshine period in a year. The sun moves
15° every hour between 6:00am (sun rise) to 6:00pm (sun set)
and stays above our head at noon. Solar irradiation in most
parts of Indonesia varies unpredictable caused by the existence of cloud and its movement. Therefore, solar cookers for
Indonesian islands should have an ability to absorb solar energy at a certain rate to create a high temperature in a short heating period. Following are the considerations to design the
solar box cooker type HS for sun cooking in Indonesia.
4) Dietz (1954) found if Fe2O3 content in the glass is high,
the glass absorbs in the infrared portion of the solar spectrum. Therefore, an ordinary glass of three millimeters
thick is placed at the upper surface of the oven chamber.
The glass will block the thermal radiation loss and also
functioning as the “upper heater” to create a homogenous
temperature in the chamber.
1.1. Physical considerations.
1) Kirchoff Law of radiation cited in Weast (1985) states “A
substance when exited by solar rays possesses a certain
power of emission. It tends to emit rays whose wavelength depends upon the nature of substance and upon the temperature”. When a black body absorbs radiation the temperature of the body controls the re-radiating and this
make the emitted radiation may have a wavelength distribution greater than that of the originally radiation. A perfectly blackbody have emittance (ε) = 1 , the ratio of e to
α (absorbtance) equal to unity.
5) Cotton is the best alternative insulator to be placed underneath the oven chamber, light and locally available. It suits
to the temperature range over which the cooker operates.
The void fraction (∋) can be well adjusted and can be
determined by weighing cotton placed in volume V: ∋ =
mc / (ρc * V).
6) Hot air naturally moves upwards. A door situated on the
upper side would release heat with no barrier when the
door were opened. Therefore, the solar cooker type HS
was designed with the door in one side of the walls while
the reflector set on the opposite side allowing the reflected
beam radiation to heat the shaded part of the absorber.
2) In order to get a better absorptance, a thin alluminium plate
paint black is used as the absorber of solar ray and to emit
heat into the oven chamber. It is a cheap alternative for a
black body.
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Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
1.2. Geometrical parameters to optimize the design.
dictated the cooker gross size, weight and price.
7) The cross section of the oven chamber is shown in Fig. 1.
AB line lies at the bottom surface of the oven chamber. CD
line at the upper surface of the chamber, where the bottom
glass is set. For HS5521; HS5921; HS6021 and HS6321,
TF = 10 cm, AB = 2.5 TF and DC = AB + 2TF = 45 cm.
The distance between the aperture surface and the bottom
absorber (T’-F ) or G-W in Fig. 2c is 18 cm. The walls of
the oven chamber (AD and BC lines) were tilted 45° to
augments the area of heat absorption and to trap greater
incident solar irradiation in a day. This consideration was
derived when the aluminium chamber still in its original
colour ♠. The directions of beam radiation per hour are
shown. Between 9:00-15:00, the center of the bottom glass
will be the hottest part, while at 12:00 all the beam is
reflected to the middle part of the oven chamber. The pan
is placed at the center of the chamber.
If A0 = Aa ,we defined FAA = 1. The previous HS7033 has
FAA = 1.033 and HS5521 has FAA =1.112
10) Suharta et al. (2000b) found that the total conduction loss
through the wall and the bottom side are small compare to
the total losses. Therefore, the optimisation considers the
ratio of insulator thickness (E-G) at the upper side over
that at the bottom side (W-In.ct), see Fig. 2c. This ratio is
named Fub. The upper insulator consists of 3 glass layers.
The solar cooker HS7534 has Fub = 1.63 (=13/8) and for
HS7033 is 1.9 (=13/7). To optimise the design, Fub of
HS5521 was made greater, that is 2.48 (=6.7/2.7). They
proves that a thinner transparent insulation in HS5521
gives a smaller temperature difference between temperature at the center of the oven chamber volume (Tov) and temperature on the middle glass (TMG), that is 13-34 C for
HS5521 and 24-53 C for HS7033. Also gives a lesser
condensation under the top glass layer. Fub relates the
cooker ability to suppress the heat loss within the thickness limitation.
8) Suharta et al. (2000a) defined a design factor (fR), see Fig.
2a and Fig. 2b. When the end of the mirror image reach
MI and crosses the aperture at MI′ , while the sun incident
angle (θ) = 45° and the reflector angle (ψ) = 90°, the mirror length (ML) is defined as the minimum length. MI′L is
the image length. At this position, different ML gives different MI′L . If the image edge is kept at MI, the longer ML
the brighter the image will be. Based on this understanding, a design factor (fR) is defined as :
fR = (MI′′L x Mw) / Ao
Since 1994, Suharta et al. has designed and tested several
solar box cookers type HS listed chronologically as :
HS8745; HS7540; HS7534; HS7033. The first three years
field experiences found that these solar cookers is too big for
the doorway since they want to keep it indoor if not being
used. Therefore, the optimisation was made to raise the
absorbed energy (S) to gain a greater useful energy (Qu) but
smaller and lighter to get a least-cost unit. The geometrical
consideration to optimise the design resulted smaller solar
cookers: HS5521; HS5921; HS6021 and HS6321. These
solar box cookers have the same aperture area of 2343 cm2
(=48.3x48.3 cm) and the same mirror width of 51 cm. The
mirror length (ML) of HS6321 is 3cm longer than HS6021 or
4 cm longer than HS5921 or 8 cm longer than HS5521. These
cookers are relatively simple so the technique to make it
could be easily transferred to the prospective users.
(1)
Ao is the aperture area. Ao = Aw x AL. Mw should equal to
Aw to get the mirror image as wide as the aperture width.
9) Before the values of each term in the equations (2), (3) and
(4) are known, we need a practical guidance in designing.
The ratio of absorber plate area (Aa) over the aperture area
(Ao) is used as guidance.
FAA is limited geometrically by the aperture area, which
Fig. 1 The cross section of the oven chamber (DABCD). DABC is covered with a thin aluminium plate. CD is the glass sheet. On equator, the solar incident angle
differs 15degree per hours. The symmetrical shape of the chamber makes the reflected lines trace back the incident lines. There are 8 different lines: the incident
beam (I), the reflected beam from the front wall (IBFW), the reflected beam from the floor (IBFL), the reflected beam from the back wall (IBBW), the beam reflected by the mirror (IR), the reflected IR from the back wall (IRBW), the reflected IR from the floor (IRFL), the reflected IR from the front wall (IRFW). The number
indicates different intensity level at 10:00 o'clock. Mark 6 means the area hits by 6 lines : I, IR, IBBW, IBFL, IRFW, IRFL. Between 9:00-15:00, the center of the
glass is always the hottest part. If T'T is the thickness of the upper cover, C"D" is the maximum aperture while CD is the minimum.
♠
Infrared diffuse percentage reflecting factors of iron oxide black pigments is 26 % for wavelength of 0.6 mm, 41% for wavelength 0.95 mm, 30% for 4.4 mm,
4% for 8.8 mm, and 9% for 24 mm, see Fischel et al. (1972: Table 6h-1).
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Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
Fig. 2 The mirror area is indented from M1 to M2. If the image edges is kept at MI the reflector angle (ψ) should be adjusted so that ψ2 < ψ2. This makes the
mirror catch the ground reflection better. θ is the solar incident angle or the angle of the direct beam with the perpendicular to the aperture surface. Φ is the
angle between the mirror image line of the top - edge of mirror and the aperture surface. ε' is the angle between the mirror surface and the normal of the horizontal surface. ψ is the angle to the mirror with the aperture surface. β* is the angle between the mirror image line of the top - edge of mirror and the mirror
surface. On equator, the condition when θ = 45° (at + 9:00) ψ = 90°, Φ = 45° and β* = 45°, is used to define the minimum length of the mirror. For θ > 45° (at
6:00 until + 9:00) ψ = 90° - ε', Φ = 90° - θ + 2 ε', β* = θ - ε'. For θ < 45° (after 9:00 until + 12:00) ψ = 90° - ε', Φ = 90° - θ - 2 ε', β* = θ + ε'. At noon θ = 0°.
2. Performance Evaluation
The average value of overall heat loss coefficient, (UL)av
was calculated from data at the quasi-steady state, which is
defined from the oven temperature profile that ripples about
noon. It is written as :
The oven temperature (Tov) profiles of solar cookers of a
certain design showed a range of performance. The manufacturing process influenced the performance. Therefore 5-40
solar cookers of each design were made and tested simultaneously during community education training. This new
concept of mass-testing, was proved effective to notice the
performance range and to avoid misinterpretation of the data.
It provided :
l
l
(τα)av
- Ta
ss
(3)
ss
I
ss
(4)
The energy losses is written as : QL = (UL)av . (Tov-Ta)
The efficiency is written as :
a chance to note performance different of the cookers that
were exposed to the sun in a different duration.
η=
(Q ) = (τα)
A (I)
u
av
(1 + ρm . fR. b) − (UL)av
(T
0
a chance to find out a possible damage by comparing the
oven temperature profile of suspected cooker with the other
cookers’ profiles, see Suharta et al. (2002; 2003).
ov
−
T)
a
(5)
(I)
(τα)av is the optical efficiency of the solar cooker. τ is the
transmittance of the transparent covers and α is the absorptance of the cooker. Duffie and Beckman (1980, p231) included a mass and heat capacity impact in the form (τα)av and
states : “If a single glass cover absorbs about 4% of the incident solar radiation, (τα)av is one percent greater than (τ∗α)”.
In calculating (UL)av , Suharta et al. (2000a) use (τα)av =
1.01∗τ∗α at an assumption that the upper glass cover absorbs
about 4% of the incident solar radiation. (UL)av is a constant
value and it is obtained from the highest temperature operation, so that an exaggeration of the solar cooker thermal performance can be avoided. The convection and infrared radiation loss factors are lumped in (UL)av At Tov = Ta , the energy
losses (QL) dismiss and equation (5) become :
The best oven temperature profile was then used to characterize each design.
Suharta et al (2000a) derived the absorbed energy in term
of incoming solar irradiation or insolation (I), the reflected
beam radiation (IR), the optical efficiency of the upper covers
(τα)av, mirror reflectance ♦(ρm),
the design factor (fR) and what so called the surrounding
factor (b) and is written as :
S = (τα)av (I + IR ) = I (τα)av ( 1 + ρm . fR. b)
T ov
=
(UL)av
(2)
Hunn and Callafel (1977) described a reflectivity value of
variety surfaces and landscape. In this paper we called this
reflectivity as the surrounding factor. For earth road surface :
b= 0.04, for light concrete surrounded by the building having
light paint: b=060, for the field with snow cover and wooded
area in a background : b= 0.73
ηTov = Ta = (τα)av (1 + ρm . fR. b)
(6)
When ηTov = Ta = 1, the value of b is maximum and is
named as bmax .
The oven temperature profiles recorded before quasi-steady state were re-plotted versus solar insolation to demonstrate its heat collection rate. Then, a method for fitting a linear
The oven temperature profile development has covered
the nature effect on the cooker performance.
Percent normal-incidence reflectance of mirror having aluminium coating, from the ultraviolet (0.26-0.42 µm), visible (0.38-0.78 µm), near infra red (0.782.5µm) and far infrared (>2.5µm), see Fischel et al (1972: Table 6g-2 sec. 6.157).
♦
λ (µm)
0.22
0.26
0.38
0.45
0.5
0.6
0.7
0.8
0.9
1
3
5
10
15
20
30
ρm
91.5
92.2
92.5
92.2
91.8
91.1
89.7
89.7
89.7
89.7
89.7
89.7
89.7
89.7
89.7
89.7
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Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
η = ηoptical − U (Tabs plate – T amb) / I
function to this oven temperature profile was demonstrated to
rate how far the design change might improve the performance, see Fig. 3.
Solar box cooker type HS has a good insulator, so equation (9) can be identical to equation (5) if
This relation is written as : Tov = ϑ (I) – Ω. This line
crosses the negative axis of temperature at W. Slope of the
linear line, ϑ , estimates the maximum temperature that might
be reached by the cooker of different designs and estimates
how low its dark ambient temperature, Ω.
η=
τα
(1 + ρm . fR. b) −
UL av
η
(UL)av
Ω = - Ta
(9)
ηoptical = (τα)av (1 + ρm. fR. b) = 1.01(τ*α) (1 + ρm. fR. b) (10)
If ηoptical was defined as (τ*α) only, then its different with
equation (10) is named as the effective concentration ratio
(Ce) of solar box cooker type HS, thus :
Ce = 1.01(1 + ρm . fR. b)
(7)
(11)
This gives a meaning that Qinput = S.
For a certain design, the value of τ, α, ρm and fR are
constant while the surrounding factor varies depending on the
test site atmosphere. Various optical efficiency (τ*α) from
0.5 until 0.78 is plotted versus (τ*α)*Ce in Fig 4. This simulation uses various ρm : 0.96, 0.92 , 0.88, 0.84 and 0.80 and fR
values of different designs. At certain τ, α, and ρm, increasing
fR lowering the value of bmax. This means lower requirement
for a higher value of surrounding factor, so that the choice to
place the cooker raise. The design having a higher fR gives a
better performance. The assessment of theoretical and experimental results shows that fR is vital as this parameter dictates
the performance.
(8)
The steeper the linear line the better the solar energy
absorbed by the solar box cooker and thus cooks faster. The
evaluation of the later designs show that the performance of
HS 6321 is better than HS6021 which is better than HS 5921,
while HS5921 is better than HS5521. Once the oven temperature profile is known, the effect of design change on the
solar cooker performance can be confirmed. The best temperature profiles of the sequence designs prove that the evolved
designs have improved the performance steadily. This means
the approach in designing is right and effective. The barrier
for further improvement is the limitation of materials used.
The performance test of 17 units HS6021 in the region with
average daily irradiation of about 6 kWh/m2 confirms this.
The highest stagnation temperature of HS6021 was 192 C,
see Suharta et al. (2003).
4. Further research activities
This research that combine design technology and a community education give multiple benefits. Those are :
l
3. Effective concentration ratio (Ce)
l
The solar box cooker type HS can be classified as nonimaging concentrator♣. The solar irradiation entering its aperture and its plane receiver distribute radiation onto all parts of
the absorber.
l
l
Bannerot R.B.(1977) cited in Donald Rapp (1980: p326)
gives several simple concentrating collector geometries,
which might be used as periodical adjusted concentrator collectors. His test result shown that the simplest single facet
(similar shape as the oven chamber shown in Fig.1) having
Ce = 1.8 is almost as good performance as the Compound
Parabolic Concentrator (CPC) Collector and surely cheaper.
l
l
to enrich a designing method in which interdisciplinary is
purged by testing,
to enrich the local knowledge about a solar technology
application to solve their primary energy problem,
to enrich the local environmental awareness
to enrich the local experience in the cultural diversity as the
international volunteers are joining the community education.
to show a learning process on how municipalities can focus
partnerships with the firewood consumers
to promote a real implementation of sustainable development.
Donald Rapp (1981: 318) writes the rate for solar energy
input to the receiver as : Qinput = I Ce hoptical where I is the total
insolation on horizontal surface in watt/m2 and Ce is the effective concentration. ηoptical is the overall optical efficiency. It is
the product of transmisivity (τ), reflectivity (ρ) and absorbtivity (α) for light interacting with all surfaces between the
entrance aperture and receiver. The efficiency is :
η = [ I Ce ηoptical - U (Tabs plate – T amb) ] / ICe
U is the heat transfer coefficient per unit area of the receiver. Donald Rapp (1981: 316) assumed that for flat plate collector ηoptical = 0.7, for flat plate collector without insulator, Ce
= 0.5 since the receiver loss heat. For one having a very good
insulator, he assumed Ce is equal to unity. The efficiency is
written as :
♣
Fig. 3 The linear trend of heat collection rate of three solar box cooker type HS 6021.
In order to get a heat collection rate some insolation data was deleted (see inset).
At the solar insolation as high as 1100 Watt/m2 these cookers might reach temperature 220C.
For non imaging concentrator, the concentration ratio is in the low range, generally below 10. For cylindrical parabolic concentrator is 212.
72
Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
4.1. Unattended sun cooking
Considering the limitation of materials used in solar box
cooker type HS, the concentrating solar cooker will be tested
in Indonesia. Dieter Seifert (2002) promoted his concentrator
cookers: K8; K10; K14 and K20 during the World Summit on
Sustainable Development in Johannesburg in August 2002.
K14 with 1.4 meter reflector diameter costs about 80 US$
suitables to provide food for 5 to 15 persons. ECSCR Test at
Almería, Spain in 1994 shows that K14 able to boil 48 litters
of water in a day. Preliminary test of concentrator cooker
K10, which having reflector diameter of 1 meter, in Serpong,
Java is shown in Fig. 5. After 65 minutes under the local
radiation on that day as shown in Fig. 5, 2 liters water in an
open pan reach 76 C. In the day of test, a thin haze and a lot
of clouds hanging in the sky. We wait another 50 minutes to
see the water boil but the water drop to 73 C. Need to focus
the reflector all the time or the temperature at focus drop
significantly. Need to test and to document its performance
for cooking in East Nusa Tenggara, West Nusa Tenggara and
South East Sulawesi, which having clear sky.
As the sun position change, it is needed to track the
cooker intermittently to keep the mirror image coincide with
the aperture. Widening the width of the mirror reflector prolongs the interval between “horizontal” settings, while lengthening the mirror length prolongs the interval between “mirror angle” settings. Based on the geometrical data the interval prolongation can be 90 minutes. As the major cooking
time is about this interval so the reflector enlargement provides a possibility of unattended cooking. Therefore, a new
design is proposed. It is named as solar box cooker type
HS63(65)21. Its reflector area is widened 5 cm at the right
side and 5 cm at the left side. In sunny day, the cooker is heated until 9:00, then it should be used for cooking. The use of
it without load will damage the heat tight, as the sealant will
be affected by its high temperature achievement.
4.2. Testing K10 performance for Indonesia
Fig. 5 The performance of concentrator
cooker K10 tested on 8 December 2003 at
UPT LSDE, Serpong, Java. The cooker
was start exposed to the sun at 11:05.
Load 1: 2 liters water in a black painted
pan having a hump at the center was start
loaded at 11:05. An empty space under the
hump reduces T load sensitivity to follow
the temperature profile at the focus point.
Load 2: 150 ml coconut oil in a flat frying
pan, with shinny aluminium colour at the
bottom, was start loaded at 13:03. When T
load = 106C there are small bubbles come
out from a shrimp crisp, which was frying.
Many cloud in the sky. Temperature oil of
156C was not enough to fry a single
shrimp crisp. Need to focus the reflector
all the time or the temperature at focus
decrease, see T load at 12:10 until 12:45
73
Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
5. Degrading environment that support the living
The need of firewood for cooking in rural area is shown in
Fig. 8. Cooking is the basic need of people. This primary-energy need grows a long the population. The forest as the source
of firewood is limited, see Fig 7, while the need of firewood
growing in speed and the ability to buy kerosene is limited,
these make the forest and the green areas become an empty
space so fast. The number of the poor in rural areas from 1976
to 2002 is shown in Fig. 9, it shows a tendency of continuous
growing. Degraded environment will further deepen the poverty level of those who depending on the surrounding environment. Regarding this sun cooking is seen as a potential tool to
support the living in barren areas of Indonesia such as East
Nusa Tenggara, Lampung, East Java, West Nusa Tenggara and
South East Sulawesi. It is the best practice.
The poorest province is East Nusa Tenggara (1 ) then
Lampung (2nd), East Java (3rd), West Nusa Tenggara(4 th) and
South East Sulawesi (5 th).
st
Poverty line (*Rp.1000/capita.month);
population live below the poverty line (%)
In East Nusa Tenggara, for examples, 6.3% of population
spend less than Rp 40,000 per month per capita; 32.98%
spend Rp.40,000 - Rp.59,999; 29.24% spend Rp.60,000 Rp.79,999; 15.05% spend Rp.80,000-Rp.99,999 and 16:43%
spend more than Rp.100,000. (1US$ = Rp.8,241 per 10 June
2003). The poverty stays and becomes chronic as they only
have 37.1% for other needs, while 62.9% of this expenditure
is spend for food, see Suharta et al. (2003). This poverty
closes related to the limited environmental condition that support the living. However, Irian Jaya shows an anomaly. East
Nusa Tenggara and East Java have a wider critical land than
its green area, see Fig. 6 and Fig. 7. Severe exploitation of
forest in the whole Kalimantan and South Sumatera left the
empty areas as critical lands.
Need to bring these findings into the attention of policy
makers at national and international level to provide a consideration to revamp the energy policy framework. Need to
break the funding scarcity in helping the poor and thepoorest
in the barren areas of Indonesia and of the world.
100
90
80
70
60
50
40
30
20
10
0
Provinces in Indonesia
Poverty Line (*Rp.1000/Capita. Month)
Percentage of Population live below the Poverty Line (%)
Fig. 6 Poverty line in rural areas by provinces in Indonesia, in 1999. The poverty line in East Nusa Tenggara is the lowest, that is Rp 66,143.- and 49.39 % of
population live below this poverty line, which means their incomes are below Rp. 66,143.
Source: Statistik Indonesia 1999, BPS (2000, p597). Note : US$ 1 = Rp 8241 per 10 June 2003
Fig. 7 The performance of concentrator
cooker K10 tested on 8 December 2003
at UPT LSDE, Serpong, Java. The cooker
was start exposed to the sun at 11:05.
Load 1: 2 liters water in a black painted
pan having a hump at the center was
start loaded at 11:05. An empty space
under the hump reduces T load sensitivity to follow the temperature profile at the
focus point.
Load 2: 150 ml coconut oil in a flat
frying pan, with shinny aluminium
colour at the bottom, was start loaded at
13:03. When T load = 106C there are
small bubbles come out from a shrimp
crisp, which was frying. Many cloud in
the sky. Temperature oil of 156C was not
enough to fry a single shrimp crisp.
Need to focus the reflector all the time
or the temperature at focus decrease, see
T load at 12:10 until 12:45.
74
Herliyani Suharta, A.M. Sayigh and S.H. Nasser /ISESCO Science and Technology Vision - Volume 1 (May 2005) (69-75)
Fig. 8 Percentage of Households by Province and types of cooking fuel (electricity / LPG / kerosene and firewood).
More than 90% of total houses in East Nusa Tenggara Province use firewood to fulfill their primary energy need.
Source : Statistik Indonesia 1999, BPS (2000, p 127).
Fig. 9 Number of poor peoples live below the poverty level in urban and rural areas of Indonesia. Since 1993 the
number of the poor in rural area increase while in urban areas start increase in 1996. The poverty level increase steeply in the period of 1993-1998.
Source: Statistic Indonesia 2001, BPS, Jakarta, p 589
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