I was serious. Solar cells are like solid state heat engines in that they’re fundamentally limited by Carnot Efficiency (which is theoretically high for solar c

I was serious. Solar cells are like solid state heat engines in that they’re fundamentally limited by Carnot Efficiency (which is theoretically high for solar cells as the effective temperature of sunlight is high). If we’re going to use “primary energy” and not useful electrical or mechanical energy, then we’d need to include the energy of sunlight falling on the solar panels, which is about 5 times the useful electrical energy produced. And just like actual heat engines, solar cells are improving. The best cells have achieved 47% efficiency in the lab, comparable to a high performance combined cycle natural gas plant (note that thermal power plants often cheat a bit by listing the efficiency in terms of the low heating value of a fuel, ie the heat produced not counting condensing the water vapor out).