I'm surprised too. I've looked into this before, and it's absolutely right - just not intuitive to me. We do have radio-photo-voltaic devices, but they're so

I'm surprised too. I've looked into this before, and it's absolutely right - just not intuitive to me. We do have radio-photo-voltaic devices, but they're so inefficient it's laughable. And we have RTG generators, which are only practical in limited situations, and again have a very low efficiency. So hot water it is!!