[RE-wrenches] Flat Panels

[Joel Davidson]

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" <august at luminalt.com>
To: "'RE-wrenches'" <re-wrenches at 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
> august at luminalt.com
>
>
> -----Original Message-----
> From: re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] 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" <solar1online at charter.net>
> To: "RE-wrenches" <re-wrenches at 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" <august at luminalt.com>
>> To: "'RE-wrenches'" <re-wrenches at 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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