The descriptions are saying they are collecting 225/450/900 KW of heat
But the tooltips are saying 225/450/900 Watts, not Kilo-Watts
I've checked prototypes (in-game with Ctrl+E) - and it seems that the Watts is the actual case, not Kilo-Watts
Anyway, which way it supposed to be?

It is very strange how no one reported this yet. No one cares of solar collectors?

That's purely cosmetic. Ignore it. There has to be a constant heat generation value, so it's chosen to be something that makes it easy to calculate the heat bonus. In reality the solar collectors heat generation is variable.

No, I mean Kilo-Watts in descriptions should be Watts - that's all
Because there is two values in the UI describing heat generation - with one 1000 times bigger than the other right next to it

I know what you're talking about. The kilowatts in the description is accurate. The constant watts value is meaningless. If you don't believe me, try using one. It works. If it was in watts it wouldn't generate any significant power.

I see. So then the other way around maybe - multiply generation values by 1000?

Then it would no longer be merely cosmetic. It actually generates that amount of heat all the time, even at night. It's just a negligible amount that has no real effect on the overall heat generation. But if it was 1000x more, then it would no longer be trivial.

It has to be set to something, so it was set at a level where you could use it as a tool to determine the real max heat generation without breaking out a calculator for the neighbor bonus.

There are little quirks like this when you try to shoehorn in non-vanilla behavior into the prototypes designed to accommodate vanilla entities and things that behave similarly to them.

Got it.
I'm sorry for that you had to take so much of your time and effort to explain this to me.
But maybe someone else will find this discussion before asking the same questions though