"Incidentally, this out-transmission of energy is pretty much the largest heat loss in solar heating panels.
Most of it occurs in the form of radiant heat loss right back out the glass/lens of the panel."
That's not really a big deal on solar hot-water systems, since the pumps turn off when the sun isn't out.
So, only the panel cools off, and not the hot-water in storage.
I remember my old hot-water panels warmed up super quick when the sun hit them in the morning.
I could hear the circulator pumps kick in pretty early in the morning.
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IIRC, there was some kind of scheme to circulate coolant up to the cool
collectors at night, to capture some of that cold and pump it down into
the warmed-up house for cooling during warm summer nights.
Not sure how that would work around here..
(Actually, indoor heat would be pumped up to the roof).