|MadSci Network: Physics|
This is a tricky one. It all depends on the amount of insulation you use. To have any chance of this working, you will need to crush the can down as much as possible first to minimise heat loss. The sun puts out a nominal energy flux of around 1400 J/m2/s at 1 a.u. (the distance to the earth). I believe you would need between 10 and 20 kJ to melt an empty coke can. This kind of excludes the use of a lens system unless you really go to town with many lenses all focussed down on the can. The alternative would be to use parabolically or hemispherically convex mirrors. For the same power, the area of mirrors required is much larger, so a logistical problem may be encountered here. You may find more optimistic news at foundry or aluminium_cycle But my feeling on this is that you will have to move the can a lot closer to the sun to get this to work. Alternatively you could capture the sun's energy as stored electrical energy via solar cells and use the derived electrical current to melt the can in an inductive or electric arc furnace. But I expect you will come up against power constraints again here. Sorry I can't be of more help. Good luck if you do go for it.
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