One of my favorite online comic sites is XKCD. If you have never seen this very unique site, do yourself a favor and check it out. One of my favorite topics to write about is solar energy. When I can combine the two, it is a happy day. XKCD humorously documents the decision tree on where solar truly works. Solar is fantastic on sites where you have some fixed real estate, there are relatively expensive energy sources, or non-existent and/or unreliable energy sources, and you have plenty of sunny hours in the day. It does not work so well on moving objects, or where it is much cheaper to find other sources of energy. This is why you don't see folks just bolting solar panes onto the family sedan. First, you would have to cart around the batteries to store up the energy, and second, the real estate just isn't there for the power needs of the typical automobile. Unless solar panels get dramatically more efficient, there isn't any way that you will get enough energy to store for your grocery runs. Follow the link, and you will see how easy it is to break it down - just pick a use case, and plug it into the comic. Brilliant!