The problem is that the heat is in the wrong place, right? We're not going to stop needing electricity. If you've got an IR beam and you can point it at something you can heat whatever it is and run a generator.

You need to cool the building anyway, so the added energy from displacing the beam to a (presumably turbine) generator would essentially be 'free.'

This is more efficient than the photovoltaic because you don't have to produce install and maintain a photovoltaic (all of which costs some energy), and you were going to cool this building with this method anyway (so there's little downside to harvesting the energy aside from complexity, which is a concern).

I assume you'd need line of sight from the panel to the generator, which it does seem would be tricky, but doesn't seem insurmountable. (Put the collector on a tower for example, in most areas of the country I think it wouldn't have to be higher than a few hundred feet). It just depends on how much heat you're displacing and whether you can collect enough to run the generator.

If it were "I'm just trying to produce energy", I'd agree that the photovoltaic is better, but if this system happened to be dual use and doing two things we already want to do, it seems like it would be a pretty substantial win.

My understanding of this is that the amount of heat transmission depends on the temperature of your target. You point it at outer space (cold), and you get a win. You point it at some sort of IR collector (necessarily at ambient temperature, or higher), and you've lost your cooling ability.

Right. One must remember that the target sink is going to be throwing radiation right back at the source emitter. Theoretically, they will exchange energy until they reach equilibrium between emission and absorption. Luckily for us, it will take a long time to heat space up enough to make a difference...

This also ties into why a magnifying glass cannot make something hotter than its source of light.

https://what-if.xkcd.com/145/

"Lenses and mirrors work for free; they don't take any energy to operate. If you could use lenses and mirrors to make heat flow from the Sun to a spot on the ground that's hotter than the Sun, you'd be making heat flow from a colder place to a hotter place without expending energy. The second law of thermodynamics says you can't do that. If you could, you could make a perpetual motion machine."

Thanks for that, it really helped me understand the problem with my thinking.

So if you point it at a satellite, or the ISS, and run a generator? Would that be a good backup power source for solar currently used?

That's a great question. The thought of an orbiting IR collector crossed my mind while typing that comment, but I didn't want to think about it hard enough to address that. :)

The "beam" this generates is really more of a floodlight than a spotlight, so only a tiny part of the energy would hit your satellite. If you could focus it down to a narrow beam which hit only your satellite, my gut feeling is that you would simultaneously be focusing the surface heat of the satellite onto your panel. So once again, your panel would only "see" a hot surface, and would lose the benefit of cold space.

Also, as others have calculated in other comments, the amount of energy coming from the sun dwarfs what these panels radiate, so you are better off just pointing your satellite collectors at the sun.

> Also, as others have calculated in other comments, the amount of energy coming from the sun dwarfs what these panels radiate, so you are better off just pointing your satellite collectors at the sun.

Especially in space! We lose a good amount of irradiation energy from the sun to the atmosphere.

The ISS has no shortage of warmth. Their challenge is keeping cool. Adding IR heat will only make things worse and require the use of more (solar) energy to remove that heat again through its cooling panels, which themselves work like this invention by radiating IR heat into space!

Low temperature thermal energy is really worthless unless it's in somebody's home in winter or another case where you need to keep things slightly warm in a cold environment. You can't store it or transport it very far at all. It's the waste product of just about every kind of machine. Look at the steam pouring out of this cooling tower -

https://en.wikipedia.org/wiki/Cooling_tower#/media/File:Cool...

Even a power station doesn't bother trying to use that for anything.

A common use is space heating in buildings in winter, but you won't be running an air conditioner in that case, nor will your neighbors want it.

You're not wrong, but it's also important to remember that they're running a heat engine to extract work. The amount of work that can be extracted is dependent on the temperature differential between the heat source and the heat sink. The water being cooled there is to keep the heat sink cold. And since the heat sink will always be colder than the heat source, they can't recycle any of that heat back to the heat source without expending energy to move it. Which would kind of ruin the point.

It's not that the heat isn't useful, or even that it's not a large amount of heat. It's that the heat is in the wrong place, and they need to efficiently get rid of it.

Maybe we could use it as a distributed way of beaming power to satellites or space probes. Have them all be capable of tilting and network them all together.