Hey all, First off, thks to everyone here on physicsforums, this is such a great resource for anything physics-related. I was thinking today about the photoelectric effect, and a scenario popped into my head which seemed counter-intuitive. Please correct me if I'm wrong, it's been a while since I've been at the University: Photovoltaic cells utilize the photoelectric effect to produce a voltage whenever an incident photon's energy is higher than the band gap of the silicon used for the cell. All matter above absolute zero emits thermal radiation, and the energy of the radiant photons is distributed by Planck's law. Planck's law implies that at all (even very low temperatures) high energy photons are radiated. Let's assume I throw a photovoltaic cell in an isolated physical system that is above absolute zero. Assuming that the voltage produced is being utilized outside of the system, how is this not an ideal heat sink?