Is it possible to make a device that could store all the heat put into it, until it builds up and amounts to something significant? It would basically be a capacitor for heat. I was thinking that since if it touched anything cooler than it, heat would drain out, so it would have to be in a vacuum. Is that correct? Also, would the heat energy escape as light faster than it could build up? I imagine that the source of the heat could be something like the Sun's rays. Again, this is only hypothetical and I just want to know why heat can't be contained and gradually built up (I'm assuming that it can't be).