[robhlt]

Air conditioners don't need to use fossil fuels. Solar power and AC work really well together because peak solar energy is exactly when you need AC the most.

No heat is created either, that would explicitly violate the first law of thermodynamics. An air conditioner powered by solar energy (or anything solar powered) ends up releasing the exact same amount of "excess" heat as the sunlight would have if it hadn't been absorbed by the panels.

[ssl-3]

They don't always overlap well -- certainly, not exactly. Thermal lag is a thing, and it is promoted by increases in both insulation and mass.

As an example of thermal lag: My present home doesn't have aircon upstairs. I've got a room with a west-facing window up there, and I just happen to chart temperatures in that room.

The daily temperature peaks in that room during the warmer months tend to happen at night -- sometimes, as late as midnight. The daily temperature minimums tend to happen around noon.

This suggests that solar power is least-useful for that particular room when solar availability is greatest. It doesn't overlap very well at all.

(I'm still looking into installing fairly modest solar rig, though, just to help offset my own baseload when I can and maybe make extended power outages more survivable.)

[thayne]

> An air conditioner powered by solar energy (or anything solar powered) ends up releasing the exact same amount of "excess" heat as the sunlight would have if it hadn't been absorbed by the panels.

Sure. But solar panels are intentionally designed to absorb a lot of energy. So if you are putting the panels over a dark surface, like asphalt, you'll probably have a net zero effect on heat. If you put them over something light colored, you are now converting more visible light that would have been reflected into space into heat. To be clear, that is still a lot better than burning fossil fuels, but it isn't completely free either.

[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.