That doesn't even make sense.
behold
this is why mathematicians should not try to play physicists outside of theoretical physics and its direct applications
because then you get dumb shit like this:
Lenses and mirrors work for free; they don't take any energy to operate.[2] 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.
Obviously, if you could concentrate heat from the sun to achieve temperatures higher than on the Sun, then you could make perpetual motion machine. This is why we, obviously, live in the current age of infinite energy, thanks to our laser-based perpetual motion machines, than generate temperatures higher than 6000 K. OBVIOUSLY
Well... Yeah? I think? I'm unsure because of your wording but you seem to be implying that he's saying that sunlight does violate conservation of energy when he's saying the exact opposite.
he doesn't say that
he says that you can't use sunlight to generate temperatures higher than 6000 K
which is obviously false because you can use photovoltaic cells to gather the energy and then use a laser to ignite things to millions of degrees (in fusion reactors, for example)
that post of his is actually choke-filled with falsehoods; I mean, he even aknowledges that moonlight is not black body radiation - and then he just, well, does this:
"But wait," you might say. "The Moon's light isn't like the Sun's! The Sun is a blackbody—its light output is related to its high temperature. The Moon shines with reflected sunlight, which has a "temperature" of thousands of degrees—that argument doesn't work!"
It turns out it does work, for reasons we'll get to later.
No reasons are actually given btw
And this one is just, fucking, fuck:
But first, hang on—is that rule even correct for the Sun? Sure, the thermodynamics argument seems hard to argue with,[3] but to someone with a physics background who's used to thinking of energy flow, it may seem hard to swallow. Why can't you concentrate lots of sunlight onto a point to make it hot? Lenses can concentrate light down to a tiny point, right? Why can't you just concentrate more and more of the Sun's energy down onto the same point? With over 1026 watts available, you should be able to get a point as hot as you want, right?
That [3] says "because it's correct", in a true assholish manner of a person that cannot even comprehend that he may be wrong
After this btw he uses some inane optics-based argument (that's also completely wrong):
In other words, you can't smoosh light beams together without also making them less parallel, which means you can't aim them at a faraway spot.
It's amazing that he doesn't know about such simple concept as "elliptical mirror", which TOTALLY CAN "aim smooshed-together but less parallel light beams" at a faraway spot
this thing is just a fractal of failure
EDIT:
Just because a "scientific paper" says something, it doesn't mean that it's actually true, or that it's true in all conditions. Such as, the usually assumed, and usually wrong, conditions of "things are in equilibrium", or a condition of "Solar system is a closed system".