[yrjrjjrjjtjjr]

You gotta take entropy into account too. Sunshine is high grade energy, infrared is low grade. Reflecting high grade energy is a huge waste. You could even (in theory) run a solar powered space-ir-dumper and end up with net cooling of earth.

[thayne]

Solar panels work by taking "high grade" energy from sunshine, doing some useful work with it, and increasing entropy by producing heat. That heat does radiate energy away at infrared wavelengths, but then greenhouse gases come into play. Greenhouse gases are very effective at reflecting infrared radiation back down to earth, so the heat is trapped.