Re: [VAC] Location of solar panels on roof

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Fred,
 Actually, the solar installation is on my 1973 25' Avion. The shape of
the trailer is much like the newer A/Ss, in that the roof profile is
kind of squared off, not nearly as rounded as my '68 A/S G.T. In any
event, we mounted the panels on either side of the front vent,
lengthwise to the trailer body. They have about 2" of clearance under
them for air circulation. These 75-watt panels are about 21" X 48" and
are mounted in frames in which we installed 4 pairs of 8-32 RivNuts.
There's 4 brackets, made from 1/8" X 2" aluminum, attached with 8-32
screws, then fastened to the roof with 1/4-20 stainless steel bolts with
a pair of rubber washers and a stainless steel flat washer at each
mounting point. RivNuts are installed into the roof for the mounting
points.

I used to use one of these panels with my A/S, mounted on an aluminum
fold-up frame (see http://www.oldengine.org/members/jdunmyer/airstream/
for details) and that worked well. Obviously, this is more convenient,
even if I can't tilt or aim the panels for optimum output. It does make
a large difference, based on my experiments with the freestanding panel
that I used on my A/S.

There are many different kinds and sizes of solar panels, but you should
do some studying before settling on a particular configuration. For
instance, 'amorphous' panels are less affected by partial shading, but
give less power in the first place. So-called 'crystalline' panels have
higher output; mine are right at 4 amps in direct, bright sun. Flexible
panels are amorphous style. Panels also come in 32 or 36 cell designs;
the former are often sold as "self regulating". The problem with 32-cell
panels is that they don't have enough overhead to do a really good job
of charging your batteries. Solar controllers are cheap and easy to
wire, so there's no reason to limit yourself with 32-cell panels.

As far as fitting panels to your particular A/S, I'd cut a piece(s) of
thin plywood or even cardboard and place it/them on the roof in your
intended location to see how they fit and look.

Once again (and I know I sound like a broken record), it's very
important to spend a bit of time figuring up your usage and doing
whatever you can to minimize it. For instance, an inverter is very nice
if you want to run a microwave or coffee pot, but they draw 10 times the
current from the battery bank as what they deliver at the 12VAC outlet.
That means that that 800-watt microwave will require 70 amps or more
from the battery; running it for 15 minutes is 17.5AH. (due to technical
considerations, it's quite a lot worse than running a 3-amp 12VDC TV for
6 hours) It's possible to operate nearly any load from a solar/battery
system except your A/C, but it comes with a cost in dollars, weight for
batteries, and roof real estate to mount the panels. Smaller trailers
are quite limited in the latter, especially, and you should keep in mind
that batteries weigh nearly 70#/each.

Phred's Poop Sheets have rules of thumb for sizing a solar system, as
does Terry Tyler's article on the Tin Can Tourist site (sorry, I forgot
the URL). Looking at them will give you an idea of what's involved.

One of the really neat things about solar electrical systems that Fred
points out is that you don't have to buy the whole thing at once. You
can start with a single panel, as I did, and add more later. I did start
with a 6-amp controller, so I had to upgrade it when I put the panels on
the Avion, but I think I paid only about $20.00 for that first one. The
panels are the big cost, running about $6.00/watt last I looked. Mine
were bought at the Dayton HamVention for about half that, easily paying
my way to that shindig.

If you're to live off battery power, you should also educate yourself on
batteries and their care & feeding. Like solar panels, they're not all
created equal, and there's tradeoffs involved. Good ol' lead-acid
batteries are still the cheapest and have the most bang for the buck. A
pair of golf cart batteries will give you a true 200AH supply, and can
be bought for about the same price as a pair of Group 27 RV/Marine
batteries that will supply only about 160AH. Also available are gelcells
and AGM batteries. These tend to be much more expensive, but have the
advantage of not needing to be vented, thus giving you more flexibility
in mounting locations.

I know I didn't give you any real answers for YOUR situation, but the
above is what I did, and so far, it seems to work well.

                                            <<Jim>>