I think you my also ignoring the potential for the creation of much more efficient collectors. Just like the first computers like ENIAC were the size of buildings, we now have computers 1000's of times more powerful, in something smaller that a deck of cards. I think the will be a breakthrough in size the will enable solar become significant. It makes no sense to suggest that we won't be able to figure out how to use the most abundant and renewal energy source in the Solar System, the Sun. It may not happen in precisely 15-years but I think it will in my lifetime, and I'm over 50. We'll figure it out.