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Cookers which concentrate light from above
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).
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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, such a dome of multiple lenses, has been tried successfully in the case of power generation.
To offset some of the problems associated with such multiple lenses, or other type of large glass lenses, 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 may blur very soon. Recently, Fatangare (1992) has also recommended these types of Fresnel lenses.
Concept VIa (Type LCA 3a) proposed by me, in this compilation suggests the use of a suitable large Fresnel lens incorporated windowsil, 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).
Large Fresnel lens had become popular for magnifying the TV screen, and when TV screens became large, some of these large lenses were put to solar application. There are many videos (http://www.youtube.com/watch?v=Wk3dv1IXb00) uploaded by Greenpower Science. Pramoters of Green power Science,Denise Rojas & Dan Rojas are indeed geniuses, and on their site, which worths the visit they have some awasome designs. (http://greenpowerscience.com/About_Us.html). They have the Death Ray Lens made with the help of Transparent plastic sheet with water on top. Another very interesting concept is about making small parabolic reflectors.
Taking a cue from such works, Bing Gu of Califirnia has designed a Solar Oven using Fresnel Lens, he has two models, 32x32" and 42x42". The ovens also come with PV operated tracking device. The design appears very sophisticated but very simple to work with. For more details visit his web page (http://california-sunlight.com/10401/index.html) and watch their video too (http://www.youtube.com/watch?v=ob0dM3vog9I)
Large Lenses are appearing in new forms. A prize winning design from Germany is a good example. It appears that this design was more for concentrating sun of special photovoltaic cells than on food for cooking though the video shows cooking food. Andre Broessel, architect, founder and director of Rawlemon Solar Architecture, ltd. is the creator of this unique lens.
CONICAL COOKERS Conical Cookers (Funnel cookers) are naturally cone shaped with a 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 waring 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)
DATS
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 higly 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.
I prefer to classify Prof. Steven's funnel cookers under this catogory. Following photo presents his innovation. 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.html)
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 rearranged 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.
Magnar is a prolific inventor, and his recent variations of Cooker the Kolumba and Voukana Solar cookers are likely to herald a new era in Solar cooking. Visit to his site is a must for all solar cooking enthusiasts. He has presented many many excellent designs. (www.heliso.com & http://solarcookers.ning.com/photo/photo/listForContributor?screenName=1h6a0jlalzd8k ).
Voukana is a bigger of the two, and as one can note it is a double cone. It can bring 4 lit of water to boil. Magnar claims that "The Voukana Solar Cooker cooks from 0800 in the morning to 1600 in the afternoon in the equatorial zone. The idea is that the cooker is inclined 30 degrees from the zenith is operational within a 120 degree sector when adjusted azimuth during the day, and the only moving part on it is the pot. ". "The technically area of this cooker is about 1,3 square meters, and optimal effect on a 22cm wide and 14 cm high cooking pot is geometrically calculated to be 1200W at optimal sun angle of 60 degrees. "
Kolumba Solar cooker&nbp; Voukana Solar Cooker (Magnar & hise able friends)
His Deep funnel cookers is also interesting. Looks a bit unsatable, but guess it can be positioned suitably. His illustrations of concentration of sun rays in a cone is worth watching (http://solarcookers.ning.com/photo/photo/slideshow?albumId=2312757:Album:1440).
PANEL COOKERS
Another very interesting,very simple class of 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 interconnected 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.
This design and many variations of this are the most popular Solar cookers of the World.Popularity of this design has compelled me to include more details regarding the design. 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 lo, 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 slightly different way in which Cookit can be cut out.
When I tried to make a '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 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 are innumerable variations of this famous and most popular Cooker the "COOKIT" designed by Prof Bernard of France. Some of the easily available designs 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 looks so simple but it is an excellent design. It is also easy to manufacture, a suitable die can be 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.
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 has been reported from Argentina 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.altavista.com/babelfish/urltrurl?lp=fr_en&trurl=http%3a%2f%2ffr.solarcooking.wikia.com%2fwiki%2fAccueil a French version of Wikia (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 out side. 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.
As I said earlier, there are many more designs of Panel Cookers. I am presenting images of some of the here. Will add at least the lins from where you can get details a little later. If you are very keen, may be you need to visit -solar cooker images - site through google.com.
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 I would, 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. It could be a very
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 VIa, 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. One more recent design of Panel cooker deserves mention here. I would consider it as ultimate in Panel cooker category. The design is called as Copenhagen Solar cooker designed by Sharon Clausson of California. It consists of just 4 reflective panels. Assembly is simple and the panels can be adjusted round the cooking vessel to capture maximum amount of sunlight. While doing so the panels are held in position with plastic clips. Following images illustrate the concept. The cooker will perform better with modified Diasanna guard.
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For
details regarding testing standards for Solar Cookers ( International
Standards ) please
click here
For Comments,
suggestions, contributions contact
Dr.
Ashok Kundapur
Email :
Please add Solar
or Solar Cooker in the subject to avoid your mail being erased as
spam