My husband and I recently went to a Self Reliance Expo and I bought a sun oven. You have the initial cost of it but after now I can cook using solar power every day and save the cost of using my regular oven, plus, in summer, I don't heat the house so the A/C works harder.
So far, I've cooked all types of soups, a chicken and veggie dinner, bread, muffins, beets and I've dehydrated a pile of spinach in it.
It doesn't have to be warm out, only bright, so even in winter, you could use it. I really love it!