The solar panels that can be bought today typically respond to a relatively small portion of the emission spectrum of the sun. Not so coincidentally, solar panels are rather inefficient, with typical output on the order of a few hundred watts per meter squared. Which inspires the question, what if we could capture 100% of the energy from along the entire electromagnetic spectrum?
Clearly, the second law of thermodynamics forbids perfect efficiency just as it forbids perpetual motion machines, but how much solar energy is there along the entire spectrum? What about from space, where our atmosphere doesn't modulate the energy passing through?