Solar cookers come in a huge variety of shapes and sizes and lots of them are great when pointed directly at the sun but performance becomes poor very quickly as the sun moves. I have been on the lookout for software to help with design since august 2008 or earlier. I finally found something useable by me. Art of illusion. With it, I compared a parabolic dish, various compound parabolic dishes and a hemisphere as the sun moves in 5 degree increments. (20 minute incriments). It is only preliminary results of course but the hemisphere wins as the best stationary dish!
Who would have thought! Parabolic dish came --- LAST!
In fairness my test was pretty crude. I just set up 7 cameras to render the scenes from directly overhead to 30 degrees off. (2 hours later). I used a red ball to represent the cooking vessel and I reason that the size of its reflection in the dish will approximate the cooking power.
Nothing was optimised. I put the ball at 000 at the xyz cooordinates and moved the dishes until the reflection image filled the dish with the camera overhead. Then I made all the other dishes invisible and rendered the scene with each camera in succession. Finally I put the 35 images in one jpg file for people to do their comparison. I have also uploaded a slightly better version of my art of illusion scene file for anyone else who wants to try this. I got a lot of help in the art of illusion forums with this and I thank them for it. The help thread is
If you use my scene file, you need to reduce the magnification from the default 100 to 1 or 2 to see the dishes The scene file should be .aoi when you download it. I have been told that it can download as .temp (Just change to .aoi and it should be fine)
Explanation of picture. With the sun overhead, all the dishes show a full red image, meaning that the sunlight will be all reflected to the red ball at the focus! So they are all equally good when pointed at the sun! By 10 degrees off (40 minutes later) a black cresent appears in the parabolic dish reflection meaning that this dish is much poorer in those conditions. It reflects conciderably less light to the red ball than do the other dishes! By 30 degrees off target, pretty much all the dishes are useless, the only red that we can see is the red ball itself. The dishes just reflect the sunlight back into space. (The people at art of illusion are not too impressed with my poor choice of magnification) etc. I should have had the red discs much bigger. Sorry
16th feb, I got help with a new scene file. If you use it, you can render a stop motion movie of jpg files of each dish very quickly, you can also move the movie timeline and your camera moves quickly.( I have video on youtube to help you get started with this.
http://www.youtube.com/watch?v=y-s2N_8tzQo is part one of software
http://www.youtube.com/watch?v=obMlr2pXXgY is part 2 It is poor quality but if you get through it, it is worth it.)
The scene file for making movies is pretty neat. It is called dishs all same size nullworks.aoi I used one frame per second and 48 frames in total
i left the 7 unused cameras so you can use them as markers as your move camera 1 in an arc over the scene
20th feb I added the 5 .mov files here for download so you can inspect how the dishes reflect light over time.
Depending on the dish, the reflection pattern is very Different! I urge people to download and inspect these quicktime movie files. They show a dish from ovehead to 45 degrees off the side.