Posted by ssb on August 8, 2008, 4:14 pm
I have an attractive proposal from a reputable local company for
installation of a "turnkey" solar hot water system for my household of
two adults. The major features of this closed loop system are one
Heliodyne Gobi 410 panel and a 119 gallon preheat storage tank for our
existing 40 gallon propane bulk water heater. The panel would be
mounted in portrait mode (4' dimension horizontal) on a south facing
wall of the house. I live in Vermont near latitude 44N, so mounting
the panel near an angle of 44 degrees would cause the bottom of the
panel to overhang the house footprint by about 7'. Not acceptable.
The company recommends mounting with a 3'-5' overhang, which
translates to 18 - 30 degrees.
The company is very resistant to my suggestion of mounting the panel
in landscape orientation (10' dimension horizontal). They say there
will be a loss of efficiency due to stratification and fluid flow, but
they haven't quantified that loss. They say there may be an
additional problem down the line with copper tubes sagging.
Other solar installers in VT & NH have Gobi panels installed in
landscape mode. Who's right? How can I quantify the trade-off?
Thanks for any advice.
Posted by ssb on August 9, 2008, 1:55 pm
Here's a bit more info that I received from the sales office of the
This fellow tells me that the Gobi line of panels is constructed with
two header tubes running parallel to the short dimension and some
larger number -- I think he said 8 -- of risers running along the long
dimension. So this design means that the risers function in
"parallel", not "series" as would be the case with a single serpentine
tube. The problem, this fellow tells me, is that there's some
probability of bubbles forming in the antifreeze/water solution in the
tubes. (He didn't quantify the probability, but apparently the
company thinks it's not insignificant.) The problem, he says, is that
a bubble can block a (vertical) tube. If the panel is in portrait
mode there are 8 vertical tubes, so lots of redundancy. In landscape,
there are only 2 vertical tubes, so a blockage in one becomes a
serious performance hit.
What I'm trying to sort out is this: Is this installer being
realistic? Are others who intall the Gobis in landscape mode taking
big risks (or passing the risks on to customers)? Why the apparent
disagreement? Under what normal circumstances would bubbles form in
the circulating fluid, anyway?