You can do a search on youtube & watch dozens of videos of solar ovens in action. They work very well!
And a solar water heater works good too. A black plastic bag with water, left out in the sun!
peace
doublejj
AGAIN. Quit watching Youtube and go TRY it , and try that Solar Still too. Do THAT prior to depending on them in a survival situation.
Beware of making too much of stuff seen on Utube , and by the way BOTH Bear Grylls and Les Stroud are a coupla damn fools , they *might* survive for three days until a rescue plain gets there , beyond that I seriously doubt it , and their cold country skills are dramatically lacking.
Want *real* practical survival skills , then watch what the folks who are living in a specific environment *longterm* are doing , not what some fool guru on the TV is doing.