I found a rear projection TV (see construction section below), took out the 2 foot by 4 foot fresnel lens and made this solar cooker. It cost me $0.00 since I used stuff I already had, either from previous projects or collected from junk (the lens, the wood came from discarded drawers.)
If you're unfamiliar with fresnel lenses see this page all about fresnel lenses.
Cooking minced pork with the fresnel lens solar cooker
The first thing I cooked was minced pork. This one took a long time to cook because I started too late in the day (6:00pm, May 31, Ottawa, Ontario, Canada) but it proved it works!
Building the fresnel lens solar cooker
The fresnel lens started life inside a rear projection TV that I found derelict sitting by the road.
Warning... In some TVs the clear plastic screen, lens and a grating with vertical grooves are all attached to the frame and when you unscrew the frame from the TV it all comes away as one. Make sure to take all those pieces apart since you want to use the fresnel lens all by itself. If you don't then you will not get good results.
In my case the lens was attached to the TV box and not the frame so I took off everything that was attached to the frame and then attached the fresnel lens by itself to the frame. That's what you see in use in my solar cooker.
Another warning... When I first took the lens home I held it in my hands and aimed it leafs and stuff. The stuff got hot but nothing burned. Rather than concluding it was useless, I decided to wait until I had it all mounted in a solid frame and I could find the focal length more precisely while the lens was more flat. I'm glad I did because as you now know, it works pretty well. So don't make the mistake that I almost did and that I know others have!
Before making a permanent mounting system I first wanted to know the focal length so I quickly put together the temporary setup shown below. Notice that I went back and took the grey plastic frame that was also part of the TV rather than making my own wooden frame.
A dry leaf held around 29" to 31" from the lens begins smoldering right away and in less than 8 seconds is on fire.
Fresnel lens solar cooker video
Adding a mirror for bottom cooking
I added a mirror to the fresnel lens so that I could send sunlight up to the bottom of a cooking pot instead of down to it. This allowed me to cook without having to wear welding goggles. Click here to see full details of this fresnel lens and mirror solar cooker and here to see how this fresnel lens and mirror solar cooker was designed.