$2 solar sand battery

Magnifying sheet from dollar store 3x magnification listed

Stainless steel bowl from dollar store

Paperclip sand filled bowl to magnifying sheet. —-x see note at end

Sunlight.

The sand can heat to over 250 C+ in the sun with magnification.

This is free energy that can be used for heating and cooking. Handle metal with oven mittens, beware of flammable items in area. Theoretically with enought sun and time, it should work marvellously!

p.s: I obviously overlooked the fact that as the sand gets hotter and hotter heating the metal bowl, the magnifier made of plastic will melt, therefore create distance between the two preferably a big distance, focus the magnifer on a stand, or makeshift branch stand to direct light to the sand.