If you want 80% + of hot water, you may need a heat disipator for the summer
for tubes ... Also, if you can angle the panel to lattitude + 15 degrees,
you will maximize winter sun and minimize summer sun. (Still may need a
disipater for summer... depends on several factors.
Some tubes have a flat collector, some have a round collector. the flat
ones can be turned to accept less sun but it requires a trip to the roof a
couple times a year.
Fredrick Skoog wrote:
Well, I'm a home brewer, so I have no direct knowledge of tubes.
As has been pointed out, solar collectors have losses. The ratio of
heat output out to sunlight energy in called the instantaneous
efficiency. This is plotted at delta ambient to collector out temp
divide by solar insolation. There should be some data on this for your
In general a vacuum tube should have have a higher efficiency under
adverse conditions. That would be under poor light and when the outdoor
temperature was low.
A very good flat plate can rival a vacuum tube collector under poorer
conditions. And there are some tube collectors that aren't very good
(low efficiency and cracking).
A well designed tube collector should be able to be used in drain
back. It'll take more care in the installation also.
Flat plate collector are less expensive (about half for the collector
itself) and you can get more collector area for the same money. Hence
more hot water under average conditions.
If you have a lot of cloudy weather and live in a very cold climate,
then a good evacuated tube collector should be your choice. If you live
in a mild sunny climate, then a flat plate. Somewhere in between and
this is more of a toss up.