panels on a bowed roof [RE-wrenches]

Sat Mar 4 09:46:47 PST 2006

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Hey Kirk,

To do PV on a arced roof and follow the arc, a few more thoughts:

1) Ideally one row would be long enough for an 
inverter string.  If the degree of arc is not 
great then two or even three rows could make up a 
string if their tilt was not more than, let's say 
5º apart.  If the arc is big enough portrait 
mounting would ensure more watts per row at the 
same angle.  Or with landscape mounting, you 
would get more "facets" but less watts at the 
same exact angle.  But this might be fine if two 
adjacent rows were really close in angle.  Two 
rows of landscape might end up with more watts 
per string than one row of portrait.

2)  If you used either a Magnetek inverter or a 
Sharp inverter you would have multiple MPPT 
channels to work with and so could keep good per 
watt inverter economics but still have more 
strings to work with.  Alternatetely you could 
use a number of smaller inverters  to match the 
rows - like a SB700 or SB1100 or the PV Powered 
smaller units. (there was a wrenches thread on 
the small configurations a while back)

Also in VT, snow and ice might want to catch in 
the Vs between the facets - another reason to 
consider a perimeter mounting system so you can 
smooth that out and get good snow shedding.

It would look really nice!  Anyone else done PV on an arc?

Have other practical considerations killed the 
idea?  or are you pursuing it?  Evacuated tubes 
solve the hot water problem?   just curious.

Best,

Jeff C.
Village Power Design

>Hi Kirk,
>
>Yes, that's one way that might work nice for the PV.
>
>Perhaps instead of trying to shim each rail row 
>to square off to the panel with top clips , you 
>could use a perimeter mounting system like 
>Sunframe or Comprail (Sunearth) or the new ITT 
>rail (www.thompsontec.com) and then each common 
>rail would be only a few degrees off of flat to 
>each of panel row - it might work depending on 
>the degree of change of your bow.  The ITT has 
>the biggest "shelf", the comprail is not much 
>smaller - those might work better than the 
>narrow shelf of the Sunframe.
>
>For the DHW, Could you perhaps used evacuated 
>tube collectors?  - then your "facet" size would 
>be your header size.  Apricus tubes are my 
>favorite.  Drainback with Apricus makes a very 
>simple sweet high reliability hot water system 
>and looks a whole lot nicer than 4 x 8 boxes.
>
>Just a thought - seems a shame to put a big flat collector on a convex roof!
>
>Best,
>
>Jeff C.
>
>>
>>Jeff,
>>
>>Its not easy to follow the arc when 4 x 8 DHW collectors have to be
>>mounted in side-by-side in portrait mode per customer request.
>>
>>I could mount multiple rows of PV panels in landscape mode, on Unirac
>>rails. The rail feet would have to be shimmed to allow the panel to lay
>>flat on the rail, and Unirac sells shims. Each row of panels would
>>"follow the arc" on its respective slope.
>>
>>Kirk Herander
>>Vermont Solar Engineering
>>802.863.1202
>>fax 802.863-7908
>>NABCEP(tm) Certified Solar PV Installer
>>Xantrex Certified Dealer Charter Member
>>NYSERDA-eligible installer
>>VT Solar and Wind Partner
>>
>>
>>-----Original Message-----
>>From: Jeff Clearwater [mailto:clrwater at earthlink.net]
>>Sent: Wednesday, March 01, 2006 7:47 PM
>>To: RE-wrenches at topica.com
>>Subject: RE: panels on a bowed roof [RE-wrenches]
>>
>>Hi Kirk,
>>
>>Again, why not follow the arc?  It would look so much better, be so
>>much easier to rack, have less uplift and support problems???  Your
>>facet lengths would be your panel width.  You simply use standoffs to
>>each panel.  Clean follows the architecture and elegant.
>>
>>Best,
>>
>>Jeff C.
>>
>>>
>>>William,
>>>Thanks for your good advice.
>>>To be clear, this is not to compensate for an old sagging or warped
>>>roof.
>>>>From a side view, the roof is not a straight slope but rather a long,
>>>sweeping arc, the slope of which varies depending on the height of the
>>>roof you're at. Call it a bell curve, sort of. It has a name
>>>architecturally, but I forget it. The challenge is to create an
>>>evenly-sloped rack to mount panels which is "tangent" to the arc and at
>>>proper tilt angle at point of mounting.
>>>After looking through some catalogs, I found that unistrut makes a 6"
>>>strut welded to a 2 hole mounting plate. They also make a hinge. So the
>>>tangent can be made by bolting one end of the hinge to the top of the
>>6"
>>>unistrut mount, then bolt unistrut rail to the top end of the hinge (2
>>>feet per rail). The rail is the tangent line running up/down the roof.
>>>Several of these rail assemblies across the roof form the base to bolt
>>>on horizontal unistrut rails and problem solved. I hope.
>>>
>>>Kirk Herander
>>>Vermont Solar Engineering
>>>802.863.1202
>>>fax 802.863-7908
>>>NABCEP(tm) Certified Solar PV Installer
>>>Xantrex Certified Dealer Charter Member
>>>NYSERDA-eligible installer
>>>VT Solar and Wind Partner
>>~~~~~~~~~~~~~~~~~~~~`~
>>
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>
>
>--
>~~~~~~~~~~~~~
>Jeff Clearwater
>Village Power Design Associates
>Sustainable Energy & Water Solutions for Home & Village
>http://www.villagepower.com
>gosolar at villagepower.com
>NABCEP (tm) Certified Solar PV Installer
>
>530-470-9166
>877-SOLARVillage
>877-765-2784
>72 Baker Rd.
>Shutesbury, MA 01072
>425 Nimrod St.
>Nevada City, CA 95959
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~

-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design Associates
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
NABCEP (tm) Certified Solar PV Installer

530-470-9166
877-SOLARVillage
877-765-2784
72 Baker Rd.
Shutesbury, MA 01072
425 Nimrod St.
Nevada City, CA 95959
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~

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