E-W Roof Tops [RE-wrenches]

[asap at podnine.com]

Wrenches,

What is the consensus on north-south ridged roof tops with perfect east and
west roof faces?  I keep running into folks that want to go solar, they just
don't have very cooperative rooftops.   I believe we've determined the pitch
question (in this list, you all remember the ASCII chart from Bill?) and
that
*********
Bill said
This chart tells us the impact of fixed orientation on annual energy
production for a
grid-connected, net-metered PV system. Do not use this for off-grid since we
cannot predict array utilization nearly as well. The interesting thing about
this chart is that it clearly shows that annual energy producting is not
very sensitive to fairly wide variations in orientation (4:12 to 12:12, SE
to SW only has about 5% loss from ideal). Moral of the story is don't tilt
your modules on rooftop PV systems because it looks like hell, costs more to
install, and often doesn't buy much as far as performance.
*********
and
*********
Hugh once said:
Tilting east and west is interesting because it creates a 'phase
shift' in the diurnal power cycle, plus a small amount of effective
shading, evening or morning. If you have a building with pitched
roof whose ridge runs north-south, you can spread the peak slightly,
by splitting the pv panels between the two roof orientations. This
leads to a more constant power production with a slightly lower
overall power peak.
*********
I've talked with John Berdner on the subject last year concerning how SB's
would react, but we had 3j/a-Si and S and W faces, and had concerns about
shading as well as having strings "crossing over," etc.  This two inverter
system performs fairly well even with one of 5 strings crossing over
orientations, although I have not done a detailed analysis of the customer's
"data" he emails to me from time to time.
*********
But now I'm wanting to know specifically about homes with 4:12 north-south
ridge lines and designing for one string to be on each E and W side, each
c-Si string feeding its own inverter, grid-tied, net-metered systems.  Both
sides of the roof would have a string and their modules at roof pitch (about
18 degrees). Is this a perfect way to do it or just a great way...an OK way?
What do y'all think?

Seems like many a suburban street grid and row housing are oriented in one
solid direction or the other, so half the homes in the area have e-w ridges
and half the homes have n-s!  Before today, I was considering having one
such home with a long n-s ridge having a 5.5kw array being flat, "hinging"
the unshaded long array up to horizontal, at just below ridge line, but only
on the East side.  This was to consider potential permitting hassle I may
have for "things being able to be seen from the street (W face seen in this
case) and to still get some later afternoon sun.  Does anyone think this
would be better than splitting strings with modules flush on both E and W
sides?

This is in Southern CA.  The aforementioned chart (for all of CA I believe)
shows that modules pitched flat OR at 4:12, for E and W facing roofs, to
have about the same loss (11-12% impact; vs. 7:12/South being 100%).  Does
anyone think tilting modules S on E and W faces is worth it?

My guess, only if you can handle the aesthetics and the extra wrenching, but
then 10% more is 10% more?  But we'd still have the E and W face splitting
question.  I like what Hugh has said but didn't see any comment after that
last year.  I understand that this arrangement would have slightly lower
peak and/or shorter duration of peak but can it be overall more output in
the course of a day?  Could we call it a "fixed-tracking array"? ;)

Also, does anyone know of PV software that can configure/compare multiple
strings/faces out for me?

Thanks!
Peter @ ASAP POWER!
asap at podnine.com

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