In
this type of solar cookers the light is concentrated from above.
Though for cooking this mode of concentration of energy from the
top is not very desirable there are several old designs which
have used the method. Many new designs have been evolved and one
of the most interesting and popular is the 'COOKIT' evolved
by Prof. Roger Bernard of France.
Water lens
Type
LCA 1 (Figure 31) is an old idea which has been tried
successfully in metallurgy. Antonine Lavosier (1743 – 1794)
had used an alcohol lens to melt Platinum (MP
17600 C).
The lens was made of two curved glass sheets joined to form a
bi-convex lens and the space was filled with alcohol. The lens
measured 130 cm in diameter and as its refractive power was
rather insufficient to form a sharp focus, an additional lens of
smaller diameter was used (Meinel, Meinel 1977).
Source:- TIDE., March 1998, 8-1, pp 1-37,
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Salaria,
Singh (1978) also advocated this idea for cooking, but felt that
there was too much heat coming from the top so they advocated the
use of a deflector to direct the focus to the bottom of the
vessel (Figure 32). Instead of one large lens, several designers
have proposed the use of a dome of multiple lenses, but De Witt C
Maine was probably the first to apply for a patent (US Patent No.
4 057 048 of 12 November 1975) (Figure 33). Here again the heat
coming from the top, that is focused sunlight, would be too much
and it would be essential to divert the focus. Besides, it may be
difficult to fabricate an assembly of lenses to have a long focal
length. Of late, a multiple lens dome has been tried successfully
in the case of power generation.
To
offset some of the problems associated with such multiple lenses,
the use of transparent Fresnel lenses was suggested (Mathur,
Bansal 1981). The IIT, Delhi group was working on various aspects
of large Fresnel lenses. Two configurations were recommended. In
one, the vessel moves and in another the position of the lens is
altered. If the cost of the Fresnel lens is low then these
designs may become popular. There would still be the problem of
durability; plastic lenses would blur very soon. Recently,
Fatangare (1992) has also recommended these types of Fresnel
lenses.
Concept
V (Type LCA 3a) proposed in this compilation by the author
suggests the use of a suitable large water lens incorporated in
the roof, and the focus diverted to the base of the vessel.
Provision has to be made to prevent the glare and also to cover
the lens when it is not used (Figure 34).
Source:- TIDE., March 1998, 8-1, pp 1-37,
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CONICAL
COOKERS
Conical
Cookers are naturally cone shaped with broader top and narrow
bottom. However as you read further you may notice that the
classification becomes rather hazy between the Conical Cookers
and Panel Cookers, in general the principal is the same in both
the cases, light coming from the Sun above is concentrated on top
of the cooking vessel.
Under
this category one of the cheapest solar cooker has been designed
by Volunteers of VITA (1961). The reflector was made of
disposable cardboard cones covered on the inside with reflective
material like Aluminium Foil (LCA 4, Figure 35). The three cones
concentrated the light on to the top of the cooking vessel. The
cones telescoped into one another for easy packing. VITA claimed
that it could be used for warming the food or cooking some dry
food.(see figure 35 above).
Prof.
Mann (1981) has improved on this design. He used only two cones,
but with better reflection and concentrating characteristics
(Figure 36). The light was focused on top of the vessel kept in
an insulated circular box underneath. This design could be a good
alternative to the Telkes type of oven. Recently, El-Sebail
(1994) too has proposed a similar design (LCA 4b).
There
seems to be renewed interest in this type of Solar cookers. Mr
Teong H.Tan fabricated what he calls as DATS meaning Double
Angled Twelve Sided Solar cooker. He thought about this design
mainly to avoid the transparent plastic enclosure/guard around
the cooking pots used to avoid heat loss. The DATS saw the light
of the day through Solar cooker Review published by the Solar
Cooking International.(Photo from SCI site)
In
India, Mr. Ravendra Pardeshi and his wife Mrs. Shobha, of Pune
developed a similar Cooker. They call their cooker as 'PARVATI
Solar Cooker'( Named after inventors Grand Mother ). It is clear
from perusal of their site that they took the clue from Prof.
Mannan’s improvement of VITA Design. But to start with they
fabricated Prof. Stevens Funnel Cooker and then settled upon the
Parvati design . Vist to their site is a must, and
their URL is http://www.angelfire.com/80s/shobhapardeshi. The two
photograph/drawing presented here introduces this type of cooker.
It is commendable that this concerned and highly motivated
husband and wife team have done lot of experiments and have
suggested that staking the vessel one above the other gives
better results than keeping them side by side.Following
illustrations are form Ravidra Pardesi's site.
Prof.
Steven has another interesting variation which he calls as
'FUNNEL COOKER' and his following photo presents his innovation.
I would prefer to classify this design under Conical Cookers.Prof
Stevens funnel has several advantages, it is simple to construct,
and also store, there is hardly any wastage of sheet, supporting
the funnel may pose problem in the beginning but one can easily
solve the problem, like for example a small hole in the ground to
hold the base of the funnel. Two small sticks, or stones could be
propped up at the back to hold the funnel in the right position.
Here at India I wish to use Stainless steel of say 28 gz
thickness. I feel it would give good result. Prof. Steven has a
new site, also linked to solarcooking site.
Mr Ravindra Pardesi and his wife Parvathi have evolved
another new design, an improvement over Stevens funnel, it is a
double funnel. I request you to visit his site for more details.
They have introduced a new kind of Line Trace diagram, which
calls for immediate attention by all the Solar Cooker Designers
and I request them to make such diagrams for all the the type of
Cookers they evolve. Ravindra's URL is
http://www.angelfire.com/80s/shobhapardeshi.
This is a very interesting and
useful drawing, my special compliments to Mr Ravindra and his
wife Parvathi on creating such wonderful and useful
drawing
Molly Baker,(from US?) has presented another interesting
variation of Funnel Cooker. The cooker is made from stiff cloth
and the inner lining is a reflector material, may be like the one
produced by Derris of Clear dome Solar. When the fold is opened
and plastic tubes are inserted at the top and bottom the
cooker will be stiff and ready to cook. The innovator has
not shown and green house enclosure, but I am sure the cooker
will perform better with one. (
http://mollybakersolaroven.com/home.htm
Innovator like Anna Pearce had evolved the Cone shaped hat of the
far east region into a multipurpose device which can be used as
Hat, as a vessel to cook food, carry water, an a Cone type solar
cooker. The diagram is self explanatory.
The Conical cooker is still in vogue, and this time the designer
is from Congo, Africa. Mr Magnar Totland presents a slight
variation of this Conical Cooker design. His site with excellent
drawings on various types of cookers is a must for Solar cooker
enthusiast (
http://solarcookers.ning.com).
The Conical cooker has slightly re-arranged rings at the base to
improve focusing. A very interesting and important feature of the
design is the improved stand as shown in the diagram, which helps
in orienting the cooker to the Sun.
Type LCA 5 (Figure 37) was an interesting model
which appeared in Popular Science 219 (6): P. 84, 1981. Here, the
cooking vessel was placed on a small platform covered with a
glass jar, and two row of plane mirror assembly projected above
this platform, so that the light came from the top (Anon. 198l
b).
Mr Magnar, now settled in Congo has another variation on this
concept. The reflector in his design has a petal like Parabolic
reflector. The design looks interesting.
The Fun-Panel cooker described bellow is a combination of best
aspects of Funnel(Conical) and Panel Cookers
PANEL
COOKERS
Another very interesting but very simple design, and naturally
very low cost solar cooker has been presented by Prof. Roger
Bernard et al. from France(1995). Brand named
‘Cookit’ (Type LCA 6, Figure 38), it is just a packet
of inter- connected reflectors. When open, they fold out into a
small bracket of reflectors around a cooking vessel kept in a
transparent container or a heat resistant plastic cover. The
cooker, probably the simplest among the lot, cheaper than that of
VITA design, does work well even in temperate zones of Earth.
This is the most popular cooker of the World.
Fig.38a,
'COOKIT' as it appears in SCI site.
Popularity of this design has compelled me to
include more details regarding the same. Prof. Bernard, the
designer of this unique and most simple design has brought out a
book in French where he has presented many more simple designs.
The Cookit is to be cut out from a cardboard of about 1 x 1
meter. Other material also can be used, for example Polished
Aluminium or Stainless steel. After cutting the cardboard as
directed, Aluminised Mylar or Aluminium foil is stuck to it. It
is then folded and as shown and prop-it-up, and , you have the
cooker ready.
Fig. 38b,
design details as in SCI site.
The above figure is from Prof. Bernard's little
book on solar Cookers. It shows more, but is slightly different
way in which Cookit can be cut out.
When I tried to make one 'Cookit' some difficulties were
experienced, especially with reference to round cuts at the top
and other details. I tried to make the whole design simpler. The
central part would be about one to one-and-a-half inch ( 5
to 7.5 cm) larger than the cooking vessel. Rest of the design is
easier to draw on the flat cardboard and cut out the Cookit. It
would be possible to calculate precisely the angle at which the
reflector at the back should be, for various latitudes. The angle
thus established will have to be incorporated in the design, and
once it is cut, it can not be altered easily.
THE CORRECT ANGLE OF THE REFLECTOR CAN BE
OBTAINED BY INCREASING OR DECREASING THE DISTANCE BETWEEN THE TOP
OF THE PANEL AND CUTTING ANGLE. IN THE DIAGRAM SHOWN, IT IS ON
THE YOUR RIGHT IN THE RANGE OF 50 CM FROM TOP. IF THE DISTANCE IS
SET AT, SAY 55, THEN THE REFLECTOR WILL RECLINE.
The cooking pots have to be kept
inside a suitable transparent cover. Simple transparent plastic
bag of even Polyethylene has been found to work. Mr.Diasanna from
Africa devised a simple enclosure of transparent plastic to cover
the cooking vessel from the top. To retain the shape of such a
cover the ingenious local inventor, used thick copper wire, or
the like.( See the diagram in the composite sketch
bellow).
But when the cover is lifted to inspect the cooking material, the
vessel gets exposed too and considerable heat is lost. To offset
this many have devised what is popularly called as 'Green House
Enclosure'. Mr David from Canada has come out with wonderful idea
and I have detailed the same. I have suggested some improvement
over Mr Diassana's Cover. The design of Transparent enclosure I
suggest comes in two parts. First part is a transparant cover,
cylindrical is shape, and a size bigger than the cooking vessel,
slightly taller too. This is suitably supported by thin but
strong sticks or Copper or Aluminium wire. The top of this
enclosure has a Chinese hat like transparent cover, which is also
supported by a wire at the edge only. I have sent the details to
the Solar Cooker Review, and so the design should see the light
of the day. I shall now present the plans and drawing for the
construction.
COOKIT' has become very popular especially after the introduction
of the transparent bag around the cooking pot as suggested by
Mrs. Barbera Kerr. Prof. Bernard himself had suggested use of a
inverted transparent bowl around the black cooking pot. Later
considering several problems associated with such a transparent
cover around the cooking pot. He had suggested use of upright
transparent bowl of a size larger than the cooking pot and had
also suggested several other modifications for easy cooking.
David ( see under other links) also recommends this and in
addition has tried to improve this idea.
The diagram above gives a clear picture
as to the assembly of black cooking pot in
'COOKIT'
This diagram shows as to how a smaller
pot could be held in a larger transperent upright glass
bowl
All the above diagrams are from David
Delaney's site ( see under other links for URL
)
There appears to be innumerable variations
of the famous and most popular Cooker the "COOKIT" designed by
Prof Bernard of France. Some of the easily available ones have
been presented here, if you feel like adding any other variation,
please send it over to me through E-mail.
Prof.
Bernard's Cookit is becoming more and more popular. Florida Solar
Energy Center has developed and tested what they call it as 'HIGH
BACKED COOKER'. Their test indicate that it performs better than
the regular Cookit,at least at Florida.It is a special adaptation
for regions beyond 35 N latitude. Incidentally this group has
done excellent work on various aspects of Solar Cooking, like
selecting good reflectors, transparent material for 'Green house'
enclosure, back support for the Cookit Cooker. A visit to their
site, http://www.fsec.ucf.edu, is a
must.
Mr. Teong H Tan working at Malaysia has evolved another variation
to Cookit. Called 'Duel Setting Panel Cooker'( DSPC) was
specifically designed to offset the high altitude sun angle near
to the tropics.
Mr. Deris has presented several similar
cooking gadgets. Please visit his sites for further details (
under other links )
All the above illustrate different types of
very simple cookers designs of which are very close to that of
'COOKIT'.
In the year 2006, Derris has come out with one more interesting
variation. Only for the sake of convenience I am classifying it
under Panel Cookers. (
http://home.att.net/~cleardomesolar/SolaReflexPyramidcooker.html)
The design is dubbed as Pyramid Cooker, and interesting and apt
name indeed. It is supposed to perform better than regular
'Cookit'. As shown in the photos the two sides of the pyramid are
made of reflector material, and the front is covered by a
transparent plastic. Third, adjustable reflector is in the
front.
Recently Dar Curtis and Louise Meyer of Solar Houshold Energy
(SHE) have come out with a sparkling Panel cooker called as
Diamond Cooker to be used with their specially designed Hot pot
of Glass. They have also won a grant from World Bank to
distribute this type of cookers.
One of the outstanding designs under this category is that of Mr
John Tilleman of USA. It look is excellent, yet so simple. It is
also easy to manufacture, a suitable dye can used for cutting out
the components from the Aluminium reflector stuck cardboard, or
even polished Aluminium sheet, with minimum wastage. I am sure
this design is going to become very popular in the near future.
John can be contacted for further details at
john.tilleman@mail2web.com
Recently I came across two very interesting designs in this
category. They appear very simple yet effective.
Richard Pocock of South Africa has been working on solar cookers
for over 17 years, and has evolved two very interesting designs
'Pentagon Star' and 'Suncatcher'. Of this I would detail on
Suncatcher. As the inventor claims, though the design looks like
a variant of 'Cookit' it has been evolved independently from
parabolic cooker. He wanted to make the parabolic cooker simpler,
probably, and had ultimately landed on sun catcher design. As the
photo would depict, the design does convey more sun light to the
cooking pot, though most of it is from above as in the 'cookit'
type of designs.
Richard Pocock's site describes plans to make Suncatcher, readers
can buy from him the design as well (
http://solarcooking.wikia.com/wiki/Richard_Pocock).
Another interesting design created by one of the prolific
designer Teong Tan. He realised that a cooker with an aperture at
60 degrees capturers most of the sun shine, as in the Funnel
cooker of Steven Jones of US. But Funnel cooker is unsatble, and
hence Teong designed a new cooker called 'Fun-panel' combining
the best features of Funnel cooker as well as cookit.
The design sure appears attractive, and preliminary studies
indicate that it performs well. Readers who are interested in
making the cooker may please visit his well created site at
http://www.freewebs.com/sunnycooker/funpanelcookerplan.htm
Teong is a very concerned and devoted Solar Cooker specialist and
some of his other designs like Dual-Angled-Twelve-Sided cooker
(DATS) solar cooker have already been added to this site. Teong
has conducted comparative study on green house enclosures as
well, and finds that Dar's hot pot works well. Details can be
found in his site mentioned above. (Study detailed in
solarcooker.org site as well)
Three more type of solar cookers, which I classify under Panel
type are added.
First one is from Mozambique, it is a large panel type, not much
cuts, and silts to make. The cooker seems to have been made
directly from a big box. Top cover of the box acts like
additional reflector, one of the side opens up to form front
reflector, while the other three sides form back and side
reflectors as in a Cookit. One can see that three side and back
reflectors are slightly pulled to wards the center to ensure more
sun rays reach the cooking pot. The idea is ingenious indeed, for
it is much simpler to cut out from an old box.
Another panel type of cooker is reported from Argentine by Studio
Xcruza. Dubbed as Xcruza Cooker, it is supposed to be designed
for large scale manufacturing in mind. Compared to Cookit, the
Xcruza cooker lacks the panel on one side. The main reflector
panels are the upper and one on the side, while the lower panel
augments further as the cooking pot is kept at a height on a
grill. This enables rays to reach bottom of the cooking vessel as
well. Another feature of the design is the cooking pot and most
of the cooker for that matter is covered by transparent plastic
sheet to act as greenhouse enclosure.
One more panel type cooker is by Andrew Kotowski from France,
here the rear reflector is curved and is made from highly
reflective material as can be noted. The cooker has some more
smaller reflectors behind the cooking pot and the lower reflector
as well. It is supposed to perform better than Cookit, may be
because of curved high grade reflector. The design has been
optimized for Europe, especially for Lorraine in France at 49 N
Lat, and was cable of cooking 6 chicken legs in about two
hours.
These and other interesting designs have been reported in
http://babelfish.altav¬ista.com/babelfish/urltrurl?lp=fr_en&trurl=http%3a%2f
%2ffr.solarcooking.wikia.com%2fwiki%2fAccueil a French version of
Wikia ( but available in English too) The site reports
developments in France, pertaining to Solar cooking, Solar
Barbeque type cooker reported here is a slight variation of
Parabolic cooker, where the Parabola is covered by a square frame
from outside. For barbeque the designer uses a grill with a upper
reflective cover, while for baking cakes they use a small box
enclosure.
The Vietnam Tennis shoe like cooker is Basket type of cooker
reported from other parts of the world as well, but the Vietnam
design appears to be neat. Vietnam Solar Serf is a regular
parabolic cooker, slightly deeper variety, but made up of smaller
rectangular reflectors. Reflector is supported on ‘A’
type frame and the cooking pot hangs at the focus from a rod
projecting up from the side of the stand. Most of such
cookers would work very well, there are reports indicating that
they have worked even in Nepal. But I feel bigger reflectors
should do better work.
One of the most simple cookers, rather the
simplest, could be that described by Deris Janette( URL under
other links ), called as Cleardome Cooker it is just a
semicircular row of plane mirrors around a cooking pot kept under
two transparent domes.
Deris's
Clear dome solar cooker
Photo of Derri's Cleardome Solar Cooker
As was indicated earlier, the cookers which concentrate the light
from below stand a better chance in the field. The best candidate
in the field is the Murthy type of asymmetrical reflector among
the parabolic reflectors. In the cookers using plane mirror
geometry the winner could be Prof. Bowman’s FIT design or
Concepts III or IV proposed by the author in this review. Another
proposal of the author, Concept V, which envisages the use of a
large roof-top lens, could be ideal in smaller towns, with
single-storied buildings, and, when the system is not used for
cooking the concentrated heat could be used for heating water or
to turn on a water pump or a generator.
Source:- TIDE., March
1998, 8-1, pp 1- 37,
For Comments,
suggestions, contributions contact
Please add, Solar or Solar
Cooker, in the subject to avoid your mail being erased as
scam
