Hacker News Reader

Comment by scheeseman486 | Hacker News Reader

They don't generate heat in the sense that heat is generated from nothing. If the AC is being powered by solar, then the energy that is powering the heat pump has already hit the earth and has become part of that system. The energy that would otherwise have hit the roofing and been radiated is more focused around the radiators, but as soon as that dissipates into the air the difference to the local climate isn't any different.

If the roof was white and reflective then a lot more of that light would be reflected, but most roofing isn't.

Your logic isn't really compatible with the laws of thermodynamics.

View on HN

Solar energy is not just infrared, and infrared is not what is used by PV solar. So not it’s not equivalent and anyway doesn’t in any way impact the extra heating effect of a new heat source on the ground.

Instead of generate heat you could say they move heat if you like, from inside to outside.

All absorbed light gets turned into heat, infrared or otherwise (I'm not sure why you brought up IR?); solar panels catch some of that spectrum. I'm not sure what argument you're trying to make here, particularly given the second paragraph seems to contradict the first; "extra heating effect" (from where does this "extra" come from?) vs "you could say they move heat if you like" which yeah, not really about what I like, that's just how physics works, can't get any more fundamental than the law of conservation of energy.

You said that AC/heat pumps "generate" heat and if they were powered by fossil fuels, in an roundabout way they do. But if they're driven by solar, there's no long-trapped energy being expelled and therefore no "extra" energy added to the system beyond what the sun is providing.

Not all light is absorbed and turned to heat, much is reflected, for PV some turned to electricity.

I think we can agree energy is conserved. Extra heating effect OUTSIDE.

AC moves heat from inside to outside, ergo outside is hotter than it would be, this is not complicated.

Yes, for a time, there is a temperature difference between indoors and outdoors. Air conditioners push heat outside. But they reach equilibrium eventually. (At night, or I suppose in the autumn).

Similarly heat pumps (which is what air conditioning is) also push cold outside when you use them for heat, so the outdoor environment is colder than it would otherwise be, again until equilibrium is reached.

Similarly your refrigerator is cold inside but makes your home warmer.

My point was just that the -net- heat added to the city is zero if you’re using solar.

Reply on news.ycombinator.com