I'm getting baked...
OK, not really but I got your attention. Last night I had a conversation with a friend's wife who is very much into all things green. She was telling me about how this past weekend the family went out to make coq au vin in a solar cooker, and I had to pause and think how cool is that. Now on the day in question, it was a bit overcast and I asked how it went, and she said pretty good. A quick internet search revealed that there are a lot of people experimenting with ways to cook using free energy as witnessed at http://www.solarovens.org/ which advertises the "Sport Solar" oven. This site has plans for making your own.
There are others, but the designs focus literally on capturing the sun's heat and concentrating it into a small area that is insulated. The principle is easy, but the control is hard. I'm not sure this is something you could use regularly but it does demonstrate that there are alternatives. A lot of our preservation in the past focused on drying foods to make them last, taking advantage of nature's energy.
Solar is extremely viable in the passive sense, from heating your water to warming a sun room. The trick is energy storage for when it is needed. I'm really glad that I had the conversation, because even though I knew of solar ovens in the past, it's good to be reminded that we are not resource poor. we just need to put our thinking caps on again and figure out a way to harness the power that we have.