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10/18/07: Further research into a larger solar heater. Though I've yet to have a completely sunny day to test my new 16x48" solar heater unit, it is still reaching enclosed temperatures of over 190 degrees. I had tested 5" depth, and it didnt seem to perform as well as the 2" deep test. As with anything else solar, less air space to keep heated is better. Otherwise, since air doesnt hold heat very well, you have greater losses through your side walls, not to mention that a bigger inside depth means more surface area to lose heat out of. The 2" deep model is the one that is able to hit 190 degrees, while the 5" deep could still get up to 180 degrees. But as only the back surface area is generating heat, excessive depth will cut down on incoming light during early morning and evening when the sun is hitting the unit from more of an angle. Having a solar heater too deep is also just wasted heat. But of course there is a trade off, because if the black surface was placed directly against or too close to the front window, you would lose a lot more heat this way. Currently, I am using 3/8" plywood for the sides of the box, just a foil wrapped 1/2" insulation panel for the back, and a single sheet of double strenth annealed glass for the front. Likely, a double paned unit will increase the performance due to better insulation, but at the cost of another entire sheet of 16x48" glass, which runs about $17 at the hardware store here. My estimates for a 16x48" solar heater is that it will be capable of putting out about 5,000 BTU's per hour. You need about 30 BTU's per square foot to heat your house, so you can figure from there how many of these units you would need to work well for your house.

10/9/07: Testing the 7.5 quart pot in the new 2007 Pearcy Solar Oven. Previous testing involved a black lid over the top of the pot filled with water. Even in the Pearcy Solar oven with insulation, the water was only getting 180-200 degrees for some reason. The reason was because of the black lid actually. It was the only surface that light was hitting in the solar oven, so it would convert infrared into heat and then lose a lot of the heat right back out the window. Since heat rises, very little of the heat would reach the bottom. So I removed the lid, so that the light actually hit the water and the inside of the pot. The inside of the pot isnt exactly black, but its a dark blue speckle, like granite. This apparently is still enough to transfer more heat into the water, because it was reaching temperatures of close to 250 degrees! So is it better to cover your water in a solar oven or not? Well if you already have a glass window, you are better off leaving it open it seams.

10/8/07: Testing the 7.5 quart pot full of water. This pot was filled with water and then tested on the Pearcy Portable Panel Cooker. The entire 7.5 quarts of water could reach a maximum of 180-200 degrees during the day. So this might prove to be too big of a container for this type of cooker that has no insulation. The pot was elevated off of the ground with a circular piece of foam with a hollow core about 2 inches. This reduced thermal conduction and loss of heat into the ground.

10/5/07: Testing the 7.5 quart pot in the new 2007 Pearcy Solar Oven. After testing for maximum temperature of an empty container within the solar oven's insulated box, the maximum temperature of an empty container in the solar oven would retain a temperature of over 340 degrees. And this is a very big container too, probably enough to cook for 8 people or more.



9/29/07: Further development of the new Pearcy Portable Panel Cooker. There is a huge gap in the market between the cardboard and foil solar cookers and the $300 Sun Ovens. The cardboard and foil types are not going to hold up very long in rain or wind obviously. So long term use is out of the question. And then there are the solar ovens that are selling for the price of a regular kitchen oven that seems to be a little over priced for the average person wanting to get into solar cooking. There are very few in between types that can perform very well at all. This is where the Pearcy Portable Panel Cooker is going to come in. The entire unit is set to retail for about $25! (plus S&H) Its going to fold up completely flat, and use the same complete fold down reflector design that is going to be used on the new 2007 Pearcy Solar Oven as well. The entire flat base is to be made of plastic, in addition to the back that will allow for precise vertical positioning. This will make the entire unit extremely light and portable for anyone to use.

9/28/07: Slow solar cookers with reflective panels only. The past week I've been working on developing an even less expensive, lighter weight, and more portable type of solar cooker. It is using the same style of reflectors that the new 2007 Pearcy Solar oven will use, making them interchangable. An oven will of course retain more heat, making it able to cook at temperatures of 350-400 degrees. This style of panel cooker does not use any glass or an insulating box. Instead, this type of cooker uses only a black pot, which is to be covered with a clear plastic turkey oven bag. This helps retain some of the heat and provide the same effect that an insulating box has, but without the insulation. I used a 7.5 quart (or 7.1 liter) stew pot that was painted flat black. The inner container when empty was able to reach 260 degrees. Therefore, this type of solar cooking design could be used for any type of slow cooking like that you would do in a crockpot. After further development, this style of cooker is going to be offered for sale on FreeEnergySolutions.net very soon because it would be excellent for a portable solar cooker, and easily compete with all other types, especially for the price.

9/19/07: Adding a fan to the solar heater. With a thermal siphoning system on a solar heater, heat will rise at 2 feet per second, which is 120 feet per minute. So we need to find the velocity of a fan now. You can find this number by taking the fans cubic feet per minute (cfm) rating and dividing it by the total square feet of duct area. In this case, a 4" wide circular fan has a total area of 12.56" square inches. Divide that number by 144, because that is how many inches are in a square foot. So there are .087 square feet for the duct area on this fan. So the feet per minute (fpm) velocity on this fan is going to be 609. I had an input temperature of 81 degrees, and with the fan running had an output temperature of 115 degrees. This means it was producing 1,768 BTU's per hour, which is a considerable increase in performance. Even though the output temperature was lower, the amount of air that was heated to 115 degrees was so much greater. So this means that a fan will provide more effecient heating output than thermal siphoning. A small fan will use such minimal power, it would greatly increase the performance of the solar heater to add a fan.

9/15/07: Reducing winter heating costs with passive solar heat. Over the past 2 years, we've heavily researched and developed Solar Oven technology, but out of that comes important knowledge that can be used for a passive solar heating design. For a 15x15" model, we have a 10" square opening on the top. When this passive solar heater we've built is set in a window vertically, with a 73 degree room temperature, it will put out 153 degrees at the top of the unit, which is 653 BTU's per hour. This solar heating design using thermal siphoning, which in short is when air is heated inside of the unit and then rises out of the top. When it rises out of the top, it pulls new cooler air in through the bottom. To maximize output in a home window, the unit can be tilted backwards to directly face the sun. This decreases some of the light that bounces off of glass at an angle. When tilted to align with the sun, it would put out 165 degrees, which is 743 BTU's per hour. However, we found that the vertical glass of a house window reflects a lot of light that could be entering your solar heater. When placed outside on a day that it was only 60 degrees out and a 15 mph cool breeze, it would put out 175 degrees, for a total of 938 BTU's per hour. For an outdoor model, a lot more work will need to be done. For starters, dual paned windows will be needed to reduce heat loss through the window. The entire unit will need to be insulated really well. And if its only 10 degrees outside, you would rather circulate air from within your house through it rather than trying to heat air thats only 10 degrees to begin with. This will require a looped duct with one going into the bottom and one coming back into the house from the top. To prevent heat loss at night, and dryer vent would be needed, as well as a thermally controlled fan that would only kick on if the box reaches the desired temperature before kicking on. But at 938 BTU's for a 15x15 square area, it would definitely be worth it!

9/14/07: Continued development on the new 2007 Pearcy Solar Oven. We've promised to deliver something bigger, better, and cheaper than the previous Pearcy Solar Oven. Our target material cost was to be about $20 per unit, but its nearly impossible to get everything needed for that price for a good solar oven. Material cost is winding up at about $27 or more, which is still great! That doesn't mean that they will retail for that much, because time in cutting and assembling all pieces must be figured into the price, in addition to outgoing shipping costs. So current estimated retail is set for $75 shipped. You can see a preview of the new 2007 Pearcy Solar Oven HERE. The final dimensions on the outside of the product will wind up being a little smaller than what is pictured actually! We just have extra space there for experimental research.

9/13/07: Parabolic trough solar cooker. I've tossed around the idea at making a parabolic trough type of cooker. Its much easier to build than a parabolic dish and requires much less adjusting. Two sides could be cut from plywood with a parabolic bowl shape cut into them and then a single sheet of aluminum flashing layed into the curve and attached down. This would provide an inexpensive and easy to build type of solar cooker. The formula for cutting a 2-dimensional parabolic side is Y=x2/4(F). For this formula, "x" is the horizontal distance from the center, "F" is the focal point desired, and "Y" is the vertical distance to the curve from any point on "x".

9/10/07: R-values of insulation panels. So how much doesn aluminum foil make a difference in insulating your solar oven and how thick of insulation do you need? Well take a look at the following table put together by FreeEnergySolutions.net and you'll see that aluminum does in fact increase the r-value of insulation. A lot of places are using this new "R-Board" because its stiffer and doesnt break as easy, but the numbers show that the foil faced insulation works better!

RIGID R-BOARD

Thickness	1/2"	5/8"	3/4"	1"	1.5"	2"
R Value	3.1	4.0	4.6	6.2	10.0	14.0

FOIL FACED BOARDS

Thickness	1/2"	5/8"	3/4"	1"
R Value	3.6	5.0	5.6	7.2

8/30/07: Increasing heat transfer from black foil to ceramic tiles. With one of the tests originally done on 8/12/07, black crumpled aluminum foil place around the front part of a 3 ceramic tiles yielded 355 degrees for a max temp. The tests done today used the same type of black crumpled aluminum foil, but they were completely sealed on the back. This did in fact increase the maximum temperature to 380 degrees, which is 25 degrees hotter than a ceramic tile not enclosed in the IR absorbing plate. So if you are wanting to retain more heat directly from your black plate in a solar oven, whatever your heat retention material is, it should be completely wrapped by the black surface used for converting infrared light into heat so that the heat retention material is completely sealed with the IR absorber. So now I'm able to have 3 ceramic tiles instead of just one and am getting within 20 degrees of that 400 degree mark still.

8/27/07: Double walled aluminum box.I've built a dual walled aluminum solar oven box from the same thick aluminum used for the reflectors on the Pearcy Solar Oven usually. The first test involved 2 walls of aluminum with a 3 inch air gap. The normal 8 sided reflectors from the Pearcy Solar Oven were used, and the inner wall of the inner aluminum box was painted flat black. This setup yielded only a maximum temperature of 250 degrees. I suspect that having the actual inner aluminum box produce the heat from infrared would expel the heat not only into the actual oven space, but equally into the air gap between the two aluminum boxes. Thus, the only actual insulation was a single wall of aluminum, not both of them. So the second test I placed 1" fiberglass boards of insulation against the outer box from the inside. So the actual aluminum box on the inside is doing the heating, and the insulation was a 2" air gap, 1" of insulation, and then a sheet of aluminum. This setup produced a maximum temperature of 275 degrees. I then did a third test, involving the black crumpled foil method. In this test, the actual IR absorbtion plate would not be the inner aluminum box itself, thus both aluminum boxes served as walls rather than just 1 wall. The 1" fiberglass board was left in place for this test as well, with the maximum temperature hitting 290 degrees. This basically proves that your infrared surface area should not be a part of your insulating wall to eliminate heat from being transferred into your insulation as much. Two more tests need to be done to test the thicker aluminum plate being placed inside of the oven, and then the same but with a single ceramic tile underneath as well.

8/13/07: Slight change in reflector angle. My current setup uses 22 degree angled reflectors. I changed the angle to 30 degrees, giving the total area of light reflected into the box an increase. It did not seem to make a difference in maximum temperature since it still hit over 405 degrees with the same thickness of aluminum used for the reflectors used for the IR absorber plate and a single ceramic tile, but it did see to increase the speed at which the solar oven would heat up. So that means the light gain is better than the heat retention of the solar oven. Improved insulation techniques would likely increase the max temp the Pearcy Solar Oven could reach. I also tested this same reflector setup with the black crumpled aluminum foil only with no ceramic tile and it would only reach about 385 degrees. So this leads me to believe even further that the rate at which heat can be produced is maximized. Improving the ability to retain the heat as its produced should lead to higher temperatures. Ceramic tiles do help retain heat within the oven as well, as long as they are only used proportionally to the size of the oven. One or two 6x6" tiles would be the most that should be used in the Pearcy Solar Oven. On a side note, if you are interested in figuring how much power a microwave or conventional oven uses, Super Grow has a great electricity cost calculator. You will need to know your electric costs per kilowatt hour by looking at your utility bill, and of course the power used by the item and amount of time it is used. The 9" coils on top of an electric range will use about 2,500 watts/hour, the 6" coils will use about 1,500 watts/hour, and an actual electric oven itself will use about 4,000 watts/hour. Microwaves vary simply on the amount of power they are stated to run at. The more power, the faster it cooks, and the faster it runs up your electric bill!

8/12/07: Ceramic tiles wrapped in crumpled black aluminum foil. To test the effectiveness of wrapping the 6x6" natural clay ceramic tiles themselves in black crumpled aluminum foil, they were placed inside the Pearcy Solar Oven. When only one was placed in the oven, it reached 365 degrees. With two ceramic tiles individually wrapped in black foil were placed in the Pearcy Solar Oven, it would reach a maximum temperature of 360 degrees. With three tiles, it reached a maximum temp of 355 degrees. It seems that each tile decreases the maximum temp by about 5 degrees. But then the trade off is that when the oven is open and then closed again, you lose only 5-10 degrees! More tiles means that it will hold more heat, but of course it will take a little longer to heat up with more tiles as well. The aluminum foil wrapped ceramic tiles where only partially wrapped on the front. If they are to be completely enclosed, this may further increase the amount of heat directly transferred into the ceramic tiles.

8/8/07: Using all aluminum boxes for a solar oven. I made a set of two all aluminum boxes for the solar oven. The inner box is a half a cube shape just like the Pearcy Solar Oven. This box is complete aluminum, edges sealed with aluminum tape, and painted black. There is a 3 inch air grap between this box and the outer aluminum box. Using the normal dual paned window unit and the 8 sided reflector, this design of solar oven reached only 235 degrees. The actual inner aluminum box itself was painted black. Therefore, the heat may have radiated equally into the oven and into the air gap between the two boxes. There was no insulation between the two aluminum boxes, so the R-value would have been very low. An air gap alone apparently will not suffice in adequate insulation for a solar oven.

8/3/07: Use of Peltier effects to produce electricity from a solar oven. The Peltier effect, first discovered by French physicist Jean Charles Athanase Peltier, is the effect of electric current passing through the junction of two different metals. Reverse effect of being able to produce hot or cold from electricity was discovered by the German-Estonian physicist Thomas Johann Seebeck in 1821, who found that a voltage existed between two ends of a metal bar when a temperature difference ΔT existed in the bar. This means that any potential difference can produce power, even if the potential difference is only temperature. My idea is that in addition to being able to cook with a solar oven, it would be able to be fitted with a Peltier plate in order to produce thermoelectric power from the temperature difference between the solar oven and outside air. The output current could be connected to another Peltier device which could be used to cool a small cooler. So you would be able to cook, produce electricity, or even cool using your solar oven.

8/2/07: More experiments in infrared surface area absorbtion. Using the same type of thicker aluminum used for reflectors, an 11x11" black aluminum plate was placed in the bottom of a 9" deep square solar oven. A set of 10 black aluminum strips were stood vertically every inch along the bottom black plate. The idea was to provide more surface area that light coming from an angle on the reflectors would heat up both sides of the vertical strips of black aluminum. However, the maximum temperature was around 310-315 degrees, only 5-10 degrees above having just a flat black aluminum plate in the bottom. The second experiment was using standard household aluminum foil painted black and then bent in an acordian fashion. This makes a 45 degree angle zig zagging up and down along the bottom. There are no shaded parts on this type of surface, but it is a smooth black aluminum, not crumpled. The maximum temp of this type of IR surface area produced in the same 9" deep square solar oven was about 310 degrees. So any type of smooth black aluminum foil in any shape isnt going to yield as much power as a more finely textured surface. One of the key problems I noticed when testing black aluminum foil in the Pearcy Solar Oven was that the aluminum foil didnt seem to transfer heat into the ceramic tile very well. It may be due to less weight on it since foil is lighter, and the fact that very little of it actually touched the surface of the ceramic tile. Perhaps wrapping a ceramic tile in crumpled black aluminum foil would increase this.

8/1/07: Trying different IR absorbing surfaces in the Pearcy Solar Oven. In the recent square solar ovens that were built, crumpled black foil seems to heat up drastically more than flat black surfaces. In the Pearcy Solar Oven, the IR absorbing surface is at a 45 degree angle to the sunlight within the box. With the same crumpled black foil in the Pearcy Solar Oven in replace of the normal flat surface black aluminum, the crumpled foil did not seem to do as well. It achieved a max temp of 320 degrees with 1 ceramic tile underneath the black foil, and max temp of 375 degrees with the ceramic tile removed from the Pearcy Solar Oven. It seems that that having the black textured foil at a 45 degree angle does not provide as much surface area for generating heat as if it is flat. Especially considering the square solar oven still reached 340 degrees with internal space nearly DOUBLE that of the Pearcy Solar Oven. I did do testing on a 11x11" wide square oven, that was only 2.5" deep with the same crumpled black foil. This reached a max temp of 360 degrees. But even with a 9" deep oven thats 11x11" wide, it had a loss of only 20 degrees with the crumpled black foil as compared to the 2.5" deep square solar oven. With a flat piece of black painted aluminum foil, no crumpling, it only achieved 310 degrees. So there is more research to be done into thin textures for the infrared absorbing plate.



7/31/07: Infrared surface area absorbtion. So what makes for a good surface area for absorbing infrared light? I can tell you a few things that DO work good, and a few things that DO NOT work. Ideally, a textured surface should have more surface area for absorbtion than a completely flat surface. Sandpaper seems like a good idea to paint black, but the glue in this does NOT get along with 400 degrees temperatures. The big bulky patio blocks do get hot, but can be too thick and heavy to be effective. Painting 1/2" clay tiles black works fairly well, and could warrant more research into. Painting a piece of glass black actually does absorb a lot of heat, but only until the glass breaks at about 300 degrees. I've not yet tried this with tempered glass, but it could likely break as well. But glass is very flat and expensive. For the Pearcy Solar Oven, we use the same type of aluminum thats used for the reflectors as whats in the oven and painted black. Its the same material, so it makes the process of gathering materials easy to do. ClearDome Solar sells some type of black aluminum foil for a price. Going with the theory of more surface area equals more heat, I crumpled some regular thin aluminum foil to give it a nice texture and sprayed it black. Its about a 20x20 piece of foil, crumpled enough to that its only 10x10" give or take. Placing this in the same 9" deep, 11x11" wide square solar oven that achieved 305 degrees with a thin piece of sheet aluminum painted black, the cheaper aluminum foil actually reached a temperature of 340 degrees! This is with an 8 sided reflector, 1" insulation box, 3-4" air gap, then inside a cardboard box. But its the same as the other 9" deep square oven that was built on 7/30/07. So simply changing the base where the infrared is absorbed has added 35 degrees. Temperatures will be higher in a better insulated solar oven. It seems that having an even thinner infrared absorbing plate does not decrease the performance. Even with a smooth piece of aluminum foil painted black, the solar oven still was able to achieve a maximum temperature of 325 degrees. So based on this breakthrough, it seems that the thinner and more textured the IR absorbing surface is, the more heat it will produce.

7/30/07: Depth of square solar ovens versus maximum temperature. On an 11x11 inch square solar oven, 9 inches deep, max temp is 305 degrees. At 4.5 inches deep, max temp is 335 degrees. And at about 2 inches deep, max temp is 365 degrees. So expect a loss of 30 degrees for every 100% deeper you make a solar oven. The total surface area for heat loss on the 9 inch deep oven would be 517 square inches. On a 4.5 inch deep oven, there is a total of 319 square inches of area. And at 2 inches deep, surface area is a total of 208 square inches. For a 9 inch deep oven, this means you are able to retain .589 degrees per square inch of internal surface area. At 4.5 inches deep, you are able to retain 1.05 degrees per square inch of surface area. And at 2 inches deep, you can retain 1.75 degrees per square inch. These were all tested with a single 1 inch thick fiberglass insulation inside of a cardboard box with about a 4 inch airgap total, and dual paned glass with an 8 sided reflector and thin black aluminum IR absorber plate.

7/29/07: Improving dual paned glass effeciency. A dual paned set of glass with a 1/4" air gap will have an R-value of 1.69 With 1/2" air gap, R-value of 2.04. With 3/4" air gap, you have an R-value of 2.38 for dual paned windows. So if you are using wood to space the dual paned glass and want to match the R-value of the glass itself, the wood will need to be 3/4" High and 1.9" Wide. Or use the option of dual wood spacers with an air gap. Two 3/4" High x 3/4" Wide wood strips with an air gap space of 1/2" would be the same R value as a solid piece of 3/4" x 1.9" wood.

7/28/07: Reducing losses when opening a solar oven. The most effecient way to do this would be to have a seperate chamber that you could slide out without opening the entire chamber inside the solar oven. This is similar to how a drop mail box or a night deposit at the bank works. You can never have access to both places at the same time. This would reduce losses when opening to put in or remove food.

7/27/07: Target goal of $20 in materials for DIY Pearcy Solar Oven Plans. My current set of plans for the Pearcy Solar Oven call for a set of materials, which you can get for about $40. I have set a new target goal of building a model that performs identically, if not better, but that can be built for $20. I was inspired to find shortcuts in making a solar oven upon seeing this article about refugees cooking with the sun. Another video is available here. Unless they are figuring in shipping costs, $20 per unit seems extremely high for something that is only made from cardboard and aluminum foil, and gets maybe only 200 degrees. My goal is to produce something that is easy to build in any country, and that is better for less cost than what there is currently available on the market.

7/16/07: How to figure how hot a fresnel lense focal point will get. Figure the entire diameter of the fresnel lense. Example, if your square lense is 7x10 inches in size, your total diameter would be 7+10+7+10=34. Take the diameter times 12, so you now have 408. Then add a base temperature of 150 degrees. So you now have 558 degrees for a focal point for a 7x10" fresnel lense. This formula is something I've been able to come up with in order to get estimates on a near perfect solar light condenser or reflectors. Check out Green Power Science for a demonstration of a huge fresnal lense. Using fresnel lenses in solar applications should be avoided due to the risk of fire, serious burns, and eye damage. I've never found an actual use for these that is safe, but still, they are pretty cool. Try my formula out on that size of fresnel lense, and you will see that it is VERY accurate, even on much bigger lenses!

7/15/07: If reflectors were as effecient as Fresnel lenses. With a 24x24" width at the top of a 8 sided type reflector, and a 12x12" focal point, you are compressing 4x sunlight into a single space, since 24x24 is 4x the size of 12x12". The maximum temperature if the reflectors were perfect would be 579 degrees. This means of course your insulation must match your heat loss to your heat gain. If you were able to compress the light into a perfect focal point, it would reach 1,302 degrees. But only a fresnel lense bends all light towards a center point. Reflectors can only bend light into a sideways position from where the reflector is.

7/11/07: Temperature of the Pearcy Solar Oven WITHOUT reflectors. On average, this design can get up to 250 degrees without the reflectors. With a base of 250 degrees for a 12x12" oven, that means with the reflectors you add 150 degrees. One square foot of light is always delivered to a 12x12 foot area. So putting a reflector with a 24x24" width will be 4 square feet, but add only 3 square feet to the already 12x12" window. This means that 3 extra square feet add 150 degrees, or in other words you add 50 degrees for each square foot of reflector space above the size of the window. From here, you can come up with the approximate temperature that reflectors will add to your solar oven, assuming that your insulation is effective.



5/22/07: Light Ramp. Rather than using large and bulky reflectors, an in-line set of reflectors that would work the same as reflectors in that they would condense multiple streams of light into a single stream. The openings on this design would still need to be aligned to the sun, and maybe even more accurately than reflectors. Since the same light may bounce mutliple times off of an internal tube, much like a periscope, the reflecting mirrors inside would need to be of high quality in order to pass the infrared light with minimal losses from one mirror to the next until it reached the infrared absorbing plate. This type of solar heating design would possibly allow for a narrower solar oven to be produced.

4/18/06: Ceramic tiles for heat retention. Air is likely the worst material for retaining heat. If you have solar oven where the only thing holding the heat is the air in the oven, you will loose nearly all of your heat when you open the oven to put food in or remove it. You need something that will hold the heat produced from a black infrared absorbing surface. All natural clay type ceramic tiles are one of the most cost effective items for this. A 6x6" clay tile can be bought for about 30 cents each. Using only one or two of these in an oven will dramatically increase the heat retention ability of your solar oven. Using driveway gravel or dirt from the ground did not prove very effective. Clay tiles allow for your oven to reach its maximum temperature still, while dirt or gravel do not. The only sacrifice is the time it takes to heat up. If you are using a single sheet of black aluminum for converting your infrared to heat, it should be in direct contact with one layer of ceramic tile. Using multiple layers of clay tiles may not prove effective, in that most of the heat will be transfered into the one in direct contact with the heat source, while the other one will spend its energy in trying to steal heat from the other one. Painting the cermaic tiles themselves proved to be somewhat effective, but adds a lot of weight to your solar oven.

2/26/06: Infrared absorber variables. Some of the variables for increasing the amount of infrared light absorbed into a black plate and retained include the surface area, surface texture, surface type, reflector size and material, R value of insualtion, R value of glass window, and heat loss in surface area of inner box (some shapes have less surface area such as a wedge like the Pearcy Solar Oven).

2/25/06: Box insulating materials. To obtain certain R-values for retaining extreme amounts of heat, you must use a combination to achieve this sometimes. The following is a list of R-values of various materials in different thicknesses.

Plywood Thickness	R-value
1/4"	.31
3/8"	.47
1/2"	.63
5/8"	.77
3/4"	.94
Glass	R-value
Single Glass	.91
Dual Glass (3/16" air gap)	1.61
Dual Glass (1/4" air gap)	1.69
Dual Glass (1/2" air gap)	2.04
Dual Glass (3/4" air gap)	2.38
Triple Glass (1/4" air gaps)	2.56
Triple Glass (1/2" air gaps)	3.23

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