Boil water just by placing it in the sun.
This is a simple process to make your owns solar evacuated vacuum tubes from any bottle and a $2 vase from Walmart. The vacuum is drawn between the walls of the outer cylinder and the inner bottle replicating a thermos with one distinct difference. The sunlight is allowed to penetrate the clear vase and is absorbed by the dark inner bottle transferring the radiant heat into the liquid in the inner bottle. The vacuum acts as a super insulator. The stronger the vacuum, the less air molecules = better insulation. This vacuum is strong enough to crush metal cans.
This is an off the shelf instant option. These tubes are very inexpensive BUT often break during shipping. Large 1800mm tubes like the one in the link are near impossible to ship without "delicate freight". There are small 20oz and 8 oz version that are sold on the net. They ship fine.