MarkB

This seems the right idea to me. The sunlight is providing an energy (heat) input, to get a high temperature you just need to insulate the system well enough that it loses heat slower than it comes in. I would be trying to design something with roughly 2 boxes, one above the other : - the bottom one would be enclosed on 3 sides (maybe partly dug into the ground?) with a glass cover on the 4th side. Light would enter through here and roughly focus on a metal receiver which would form a pillar of some kind inside the box. - the box on top would be your chamber to put stuff in and would sit on top of the heated pillar. This would be heavily insulated on all sides and the top to retain the heat rising from the heating element. You would need a air escape somewhere and I imagine that would be best as some kind of hole/pipe at the bottom of the oven chamber leading down to minimize hot air loss. The idea is that light doesn't have to be accurately focused on the heating pillar - my understanding is that it doesn't make any difference how tight you focus it, a given size of lens is going to supply the same total energy whether it's going into a half-inch spot or into a 4 inch spot ... the point is that you want to keep that heat in there. So you enclose the heating element behind glass/similar and cover the oven itself up completely. (I'm not good on insulation at these temps, so suggestions gratefully received.) A question from me - how many hours would this need to be getting the sun? I'm wondering if you could half-dig this into a South or SW facing slope to help with the insulation? I'm thinking maybe a foot wide window, with an 8 inch heating element a couple of inches behind it, would allow a fair range of angles, assuming your lens arrangement could be moved around it ... MB

Hi all, I'm a computer/maths type guy and I've found this place via a link to the discussion about charcoal makers - great thread! I'm more of a programmer / theory type guy so am unlikely to get round to building actual physical "things", but hopefully I can help out occasionally with a bit of maths or theory or something ... Mark