I'm excited right now because this idea works! Last week I cooked some carrot cake in a really cheap and simple solar cooker. I got a windowshade at D.I. for $1.50, used a canning jar spray-painted black for a cooking pot, and fastened the edges of the shade with metal brads (like you use in kids’ projects). I set it outside, angled it so my shade fell right into from in front, and left it for an hour. Yummy! Not only that, but my 'carrot cake' was just my simple muffin recipe with cinnamon, raisins, and a handful of dried (not reconstituted, either) carrots from the Family Home Storage Center.
So how did I make it? Mine looked like these two solar cookers- the first uses that car windowshade, and the second just uses cardboard and aluminum foil. Both designs are VERY similar, they just use different materials. Use what you have; if you didn’t have aluminum foil but had one of those Mylar emergency blankets, you could use that. Solar cooking works best from March through October, though you can still use your solar cooker in the cooler months. It helps to put the cooker against a south-facing wall, to get more reflected energy, during the ‘off’ months. Here’s the first link: http://www.solarcooking.org/plans/windshield-cooker.htm . The other version (from Dr. Steven Jones @ BYU) is made with cardboard and aluminum foil; the website has great info on why, how, and what to cook, including cooking times. You can even make ICE with a solar cooker. No kidding. It's at http://solarcooking.org/plans/funnel.htm This link also has cooking times for different types of food.
To cook a meal for a family, one way to cook a bigger amount is just use a bigger container. Maybe layer multiple containers? Or layer food in one container. Usually not every part of a meal needs cooked, anyway. I have pans that stack together, to cook things simultaneously. You could also use a gallon-sized glass jar painted black; I got a couple from a store that makes chocolates. They got the jars when full of maraschino cherries, and sold them to me (empty) for $1. But any container that is dark (black or dark blue) can be cooked in. Maybe use a Dutch Oven or enameled cooking pot.
And if you wonder why the instructions for the foil/cardboard solar cooker say to put a wooden block under the jar/pan before cooking, I found out why- it's to keep heat from escaping out from underneath. The first time I cooked with this, my carrot cake was a little underdone on the bottom. Apparently that's why.
I have also baked cookies in my van window. I was told that it has to be at least 95 degrees outside for that to work, it gets to about 250 degrees in the window that way. I tried it on a slightly cooler day (93?) and it worked, barely. Now if you put the food next to the glass, and put a sunshade BEHIND the food, on the dashboard, that might give you a much warmer (and bigger) cooking spot. Hopefully it doesn't bake your dashboard! The glass IS tempered, though, so that part should be OK.
You can also use a vehicle for dehydrating food because it gets so hot. Just be sure to open windows a bit for airflow. ( I haven't tried that one yet, though.) You can use clean window screens or an old screen door for a drying tray. Cookie sheets work, too, but drying will take a little longer because the bottom can’t get air.
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Those of you who planted potatoes this year probably now have those delicious, creamy ‘new potatoes’ ready. (Or just use whatever kind from the store….) Maybe try cooking these in your solar oven!
2-10 potatoes- however many you want
1-2 Tbsp. vegetable oil
Seasoned salt, dry ranch dressing mix, or Parmesan cheese
Heat oven to 450 degrees. Wash potatoes well, then cut into strips or wedges about 1/4-1/2-inch thick , unless they're 'new potatoes'; leave those whole or cut into bite-sized pieces. Put them all in a bowl, drizzle the oil over them, and then sprinkle a good amount of seasoned salt, dressing mix, or Parmesan cheese over the top. Stir well and add more salt or cheese if it looks like they need it. Spread potatoes out on an ungreased cookie sheet. Bake for about 15-30 minutes or until lightly browned and tender when you poke the thickest one with a fork.