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mounting panels on a misshaped roof?

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Posted by elijahs@gmail.com on August 25, 2008, 10:06 pm
 
Hi, folks; I'm looking for advice:

I've been living in a cabin in Hawaii for years now, getting along on
the simple solar system I inherited when I got here - a few old panels
on a rusty rack on the roof; 10 gauge wire going down to an old 15 amp
PCM charge controller, and a collection of old 6v batteries.

However, recent events have necessitated me upgrading this beastie.
The
most obvious room for improvement that I can see is the location of
the
panels - where they are now, they are surrounded by trees (the jungle
grows close to the cabin) so they only receive good sunlight when the
sun is directly overhead.

What I'd like to do is figure out a way of placing them on the peak of
the roof, not on the top of a shed that sticks off the side.  This
would
place the panels in a position where they would receive much more
direct
sun, as they would be about as high as the surrounding trees.
However, this is a steep roof - 45 degrees slope - and the peak runs
north-south.

I've been online all evening trying to find a good mounting option;
however, all the modular mounts I can find are for mounting directly
to
the roof, and that won't work here.  I thought for a while that
maybe I could poke a pole up through the top of the roof and mount on
that using a pole top mount but everything I read says you need to
embed
that pole in concrete.  Is that true?  is there a way of doing a pole
mount through a roof?

Do you see my predicament?  no existing structure gives me something I
can place a few panels on and get a good angle that's out of the
shade.

a few notes:

  during the summer, the sun goes directly overhead (actually, a bit
to
the north) so I'd like to be able to adjust the panels to get close to
laid back flat at that point

  it rains a lot here, so we have big overhangs - like 4'+.  i thought
of a south wall mount but the overhangs, plus the above mentioned sun
path
during the summer, makes that impractical

  many of the trees in question are sweet old growth native forest;
I'm
loath to top them for my project

  there is no close place that there aren't tall trees around (for a
ground pole mount)

I guess what I've imagined all along is forming a sort of aluminum
"table" that spans the ridgeline, with four legs going down and tying
into the roof rafters, two on either side.  These four legs would be
tied together with a horizontal square of metal, which forms a flat
plane (the tabletop, without any actual tabletop to it) that I can
build
a regular strut-mount on.

Is that my best bet?  At best it will be a hack job and I'm a little
nervous to just dive in on something that's going to be punching holes
in the roof and exposing expensive panels to winds, etc, without
anyone
else taking a look at it.

alright, thanks in advance for any help!


e

Posted by bealiba on August 25, 2008, 11:19 pm
 

You can start with

http://s78.photobucket.com/albums/j103/GGhio/

and look at the drawings for the panel rack. This rack can be modified
to suit almost any structure.

What is the roof made of?

Posted by elijahs@gmail.com on August 26, 2008, 11:21 pm
 On Aug 25, 1:19pm, beal...@gmail.com wrote:

those drawings are great - is that your design?

the roof is a corrugated metal roof, directly onto purlins onto
rafters.  The spacing on rafters & purlins is rather wide but I can
beef up areas and tie in right next to the rafters.  It looks like
you're specifying a foot that has holes spaced as wide as two ridges
on the corrugate, and you bolt through the purlin below.

What material are you specifying there?  stainless or aluminum or just
heavy pipe?

It's kind of hard for me to tell - is there just one support leg for
that array of panels or is there one at each intersection of 4 panels
or?

and lastly - this is something I've been dreaming of playing with -
how would you modify that design to allow for a tracker setup?  could
there be bearings placed at the top of the uprights, supporting a
horizontal pipe that had crossmembers holding the panels, and a linear
actuator + one of the Redrok trackers to pivot the whole thing?  I'm
not a structual engineer so the limitations of that sorta thing aren't
instinctual...

awesome stuff....  thanks

Posted by bealiba on August 27, 2008, 3:11 am
 
Yes, based on a friends prototype.

Power drive screws or bolts if the timber is a bit sus.

The uprights are 40mmx40mmx2mmgal square gal tube

The struts are 40mmx40mm gal angle

The pivots are 32mmN/B gal water pipe. Medium wall

The pipe that holds the panels is 25mmN/B. Medium wall.

The feet are stainless.

It would depend on what sort of wind loading you have.

I have a modification to make mounting bearings easier. They can be
real buggers to align properly. But, yes this rack can be made to
track.

If you want feet I have a box full. You can have some for the price of
postage. They need to be drilled for the width of the iron on your
roof.



Posted by elijahs@gmail.com on August 27, 2008, 4:58 am
 

can you give any details or photos of this?  this is my long-term
interest, but I'd like to just get the panels up there to start
with...


you mean the stainless bits?  that's a really nice offer - my only
concern is that you're giving metric dimensions, which means you're
probably in a pretty expensive place to stuff to/from!


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