My first experience with a solar oven was in Girl Scouts. We coated the bottom and lid of a cardboard box in shiny aluminum foil. Half was placed in a shallow pit in a sunny spot, our homemade mini pizzas were placed inside, and the lid was placed on top.
It took about 2 or 3 hours for the cheese to melt, and that was a warm summer day with lots of sun.
Obviously, solar cooking works best in hot, sunny climates.
The mid-Atlantic is not as good as some other places, but there are days when it's "hot enough to fry an egg on the sidewalk" as the old expression goes.
I know someone who uses her car trunk as a solar dehydrator in the summer!
We planned to do experiments with solar cooking on our urban homestead since we have a nice sunny yard that faces south. We tried two types of ovens. I am delighted to finally be able to report the results.
The first one we tried is a very basic type that sort of looks like a funnel made of lightweight refective material. You place your pot inside a plastic bag to contain the heat and build it up.
It was cheap to purchase (sorry, don't know the brand name or where we got it), and it is very portable, perhaps a little too portable because it would blow away on a windy day!
Ours never actually blew away, but it was impossible to keep the panels angled properly on a mild day that we didn't think was very breezy.
This style works best on those very hot and sunny summer days when everything is still. It also helps if you have some extra bricks to hold it.
We finally purchased a Solavore Sport Solar Oven. This type can change angle with the seasons which suits us great since we're in the mid-Atlantic region.
It is lightweight enough to move easily but sturdy enough to stay put.
This design is more like a box with a clear cover on top, so you don't need the plastic bag around the pot as with the more basic oven we tried.
We did end up putting a black trash bag around our white Corningware dishes to help them heat better. It still fit inside the oven cover.
You need to have a lid to keep the moisture in what you're trying to warm up otherwise you'll do high-temperature dehydration instead of cooking.
We've mainly used our ovens for reheating leftovers such as things I previously cooked in the Instant Pot. It is a long cooking process more like using a crockpot than an oven since there is no specific temperature.
If you want to boil water or do something like stovetop cooking, try using a rocket stove.