silentgoodbye

Hello! I am in no way, shape, or form a scientist. I would consider myself smart, but I wouldn't consider myself educated. I have always wondered about reverse engineering and how one goes about it. You see, I've always looked at heating pads and electric blankets, and wondered, "we can use electricity to create heat, why can we not use heat to create electricity in a wrap or pad type format"? My main reasoning has always been because of cars. Why we can't create a type of film that can be applied to the outside of the car with thermo-electric receptors in them to create electricity from the heat absorbed. I would appreciate it if someone can fill me in on why it can't be done, why it hasn't been done, or if it has what the product is called. A specific scientific explanation and then a lay-man's explanation would be much appreciate as well. I'm sorry, but I didn't know exactly where to post this, so any moderators please feel free to move this where it is needed.