In 1982, while leafing through an Edmund Scientific catalog, I came across an item with the headline "Melts Asphalt in Seconds!" It was a giant Fresnel lens, 80cm x 100cm (about a yard square), which would capture close to a kilowatt of solar energy. The idea of a lens that could "melt asphalt in seconds" was frankly appealing. I already had a 30cm (1') square Fresnel lens, also from Edmund Scientific, that I had bought about five years before, and while it could be used to ignite wood and such, it was no asphalt-melter. This new lens should have almost TEN TIMES the POWER, an exhilarating thought. It cost $105, quite a sum for me at that time, but I had to have one.
After receiving it, I found that it did perform as advertised. I built a frame for it and had fun using it to make combustible objects burst into flame, melting golf balls (the rubber cord inside comes writhing out in a most animated fashion), and generally obliterating things. In 1998 I built an altitude mount for the lens, with a tray positioned at the focus on which to place objects to be Seen by the Sun. Not having to hold the lens made it a lot more fun to play with. It made it possible to boil water, melt lead, and such.
On the Summer Solstice in 2000 I first cooked with the lens. At the focus, the Sun's image is about 1cm (½") across, but at this intensity (ten thousand suns) anything is incinerated. Some experimentation showed me that moving the pan out of the focus so that the irradiated area is about 10cm across would be best for "high heat" cooking. I bought a 15cm (6") pan made of cast iron, black so that it would absorb as much as possible of the light.
If the beam could be directed at the bottom of the pan, almost anything could be cooked. But the lens directs light at its focus from above, and reflecting that light is not really feasible. If I built an black oven, I could bake things, but that isn't very interesting. What I'm left with is frying things that can be exposed to intense light. The only foods I've found so far that work reasonably well are bacon and sausage. Even those are somewhat problematic: if any part of the meat is charred (which inevitably happens), it becomes black and so absorbs much more light at that point, and the charring snowballs (a curious term to use to describe escalating combustion!) But even so, with attention I'm able to cook those items pretty well, and it's fun.
I get out the Lens a few times a year, sometimes bringing it to Burning Man where people enjoy using it to destroy things, explode cans of beer, etc. And I get it out every Summer Solstice now, and cook some bacon & sausage :)
I've received some requests for information about the lens frame and mount I made, and so have drawn up some (partial) plans for them.