Having made hot water solar heating that uses simply thermosyphon principle, using a bout an 8 gal. plastic pail with lid, 1/2" dia copper household piping with 90 deg elbows, all soldered, with a half days exposure to the Michigan (USA) sun it was more than hot to bathe/shower in.
Hence I suggest using scrap aluminum, be it heavy foil pans/cans etc, of same size, and arraying the pans via a simple rod embedded in a wood block same size as the pans. You also need a dished backer, perhaps even a 'simple' large plastic bowl or such. Locate the center of focus for your hot spot via an x'd string, now you simply start epoxying the pans edges to the dished backer. Continue in this manner, clipping sides of pans so you get
max coverage. Voila. Recycled cheap solar cooker for whatever you want, even a cup
of Java, be it instant?
It WILL work.
LarryinMICHIGAN USA