Don't get me wrong. Flat panels get dirty and raised frame edges collect
dirt. Monitor the system output to determine when to wash the array. The
economic trade-off is kWh lost to dirt vs. cleaning costs.
----- Original Message -----
From: "August Goers" <[EMAIL PROTECTED]>
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>
Sent: Wednesday, November 05, 2008 2:52 PM
Subject: Re: [RE-wrenches] Flat Panels
Joel and Bill -
Interesting dialogue... My point was that flat panels won't wash off in
the
rain because heavy sediment (dirt) can't flow over the module lip.
Instead,
it continues to build up to a point where it clouds rows of cells. This is
what we see here very clearly in San Francisco.
It sounds like Bill is trying to say that Velux puts a minimum tilt
requirement to their installations for a similar reason. That said, I've
seen plenty of arrays tilted to 5 or 10 degrees which clean off just fine
in
the rain. Sure, there is a sediment layer at the very bottom of the module
lip but it doesn't affect the output because it isn't covering the cells.
It
is only flat panels that get that really dark sediment stain covering a
significant portion of the panel.
I suppose Joel has a good point that areas that don't have lots of
airborne
debris and lots of good heavy rain might be ok with flat panels. I just
don't have any experience to prove that one way or another. It is a good
point that location could make a big difference.
Best,
August
August Goers
VP, Engineering
Luminalt Energy Corporation
O: 415.564.7652
M: 415.559.1525
F: 650.244.9167
www.luminalt.com
[EMAIL PROTECTED]
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Joel
Davidson
Sent: Wednesday, November 05, 2008 7:04 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Flat Panels
It's not as simple as tilt angle. Modules in Los Angeles (34 degrees
latitude) at 35 and even 45 degrees tilt get dirt buildup caused by night
and early morning dew and dust and no rain to wash the buildup. Flat roof
arrays stay fairly clean in locations with regular cleansing rainfalls.
----- Original Message -----
From: "Bill Loesch" <[EMAIL PROTECTED]>
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Sent: Wednesday, November 05, 2008 5:51 AM
Subject: Re: [RE-wrenches] Flat Panels
Hi August,
For what it is worth, Velux, one of the premier skylight manufacturers,
limits the minimum angle of the roof (and the parallel skylight) to 15
degrees. With the roof windows/skylights the customer has direct
observation
of how much puddling and subsequent dirt is blocking the window.
Anyone care to estimate just how much performance is lost with 5-10
degrees
off optimum tilt vs.no "ring around the collar" improved performance?
Bill Loesch
Solar 1 - Saint Louis Solar
----- Original Message -----
From: "August Goers" <[EMAIL PROTECTED]>
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>
Sent: Tuesday, November 04, 2008 8:43 AM
Subject: [RE-wrenches] Flat Panels
Wrenches -
Lately we've been called out to repair or upgrade several ~5 year old PV
installations in the Bay Area. It is always interesting to see how
they're
holding up. Apparently it was common to mount panels completely flat
(horizontal) on flat roofs back then. This poses a serious problem
because
the module frame lip catches water and dirt and prevents the panel from
washing off in the rain. See a photo here:
http://luminalt.com/temp/flatpanel.JPG
Note that two of those panels were broken by a baseball, but you can
still
see the dirt buildup on the adjacent panels right across all three rows
of
bypass diodes.
Any ideas on what percentage loss that dried dirt is causing?
Lesson learned: never tilt panels below 5 degrees, preferably 10
degrees.
Cheers,
August Goers
Luminalt Energy Corporation
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