Richard Bates wrote:

3. Do not believe ignoramuses who suggest that you will not get much heat -
that did apply to the old flat panel stuff, still being sold by B&Q, but the
vacuum tubes now being used on the continent are vastly superior. I recently
went to a demo and noted a cylinder water temperature of 48 c being obtained
on a relatively cloudy and cool day. I am reliably advised that on a warm
summers day, the tube manifold can reach well over 100 c and hence so much
heat is being soaked up that one can have 3 to 4 free baths and still have
to dump excess heat into a loft radiator - that's how good they are.
4. If you have already signed up and paid a deposit for a flat panel system
do your best to get out of it.

You'll notice the thread is posted to uk.d-i-y as well as other ngs.
This tells me the OP is in Britain.

First, flat panels give much better ROI than vac tubes
Second, British winters are mostly overcast, and flat panels work ok on
indirect sun, whereas silvered evacuated tubes work a lot less
efficiently under these conditions.

3rd, it is all more complex than that, but suffice it to say that flat
panels are very much a going concern in Britain.

An optimally designed system would have a mix of both flat panel and
vac tube, with each heating a separate part of the system. Flat panel
is best for mid-temp water, as it gives much more output per £/$. Vac
tube is best for the final max temp water, as it gives high output
temps that flat panels cant consistently deliver. However, the ROI on
the flat tubes will be much poorer, so spending some of the money on
flat panels will much improve total annual output.


NT