ballast pans [RE-wrenches]

[Jeff Clearwater]

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Hi Kirk,

We recently did a look at various ballast systems for a small
commercial install and discovered a few things.

The FS system gets away with low weight and integral frame/plate
design by keeping their tilt at 5º -  - typical of large commercial
systems tilts.   The loss of total energy by going with a flat tilt -
even in northern climates is not seen as sufficiently large  - not
large enough to justify the expense of tilting - mostly due to
exponentially increasing wind load as you tilt up (and reduced total
KW having to space rows).  The ballast gets heavy fast as the tilt
increases.

For smaller commercial systems (< 30 KW) John Randall at DPW
generated a series of drawings/quotes for us for 30º, 20º, and 10º
tilts that utilize a very simple frame that holds concrete pavers in
1.5" 2" and 4" sizes.   So you can get some good tilt with a ballast
system if your roof can hold it.  Additional dead load psf was in the
order of 6-18 psf for the ballast/racks/panels.

The advantage to tilt in northern snow climes is as much snow
shedding as it is increased energy production.  You can still get
87/91/94 % of total energy production at a 0 /5/10º tilt
respectively (Worcester, MA data) but you'll lose quite a bit to the
snow not having a place to go at those tilts.  I'm pretty sure that
the NREL data is theoretical, it doesn't take into account the snow
shedding factor (or the rain washing off dust factor that diminishes
greatly at flat tilts).

But if you really need ballast mounts but wanted to go with a steeper
tilt than the 5º that Schott offers, then give Jeff Randall at DPW a
call -  (and then hire an extra guy to move the concrete pavers from
the crane to the racks.)  A nice simple system.

Nice meeting you at SolFest, Kirk,

Peace,

Jeff C.


>Group,
>Are there any good systems out there to ballast a tilted roof-mount array? I
>have to avoid penetrating a flat roof on a commercial building.
>
>thanks, Kirk
>
>Vermont Solar Engineering
>a Xantrex / Trace Certified Dealer Charter Member
>Kirk Herander
>PO Box 697
>Burlington, VT. 05402
>www.vermontsolar.com
>www.backeastsolar.com
>800.286.1252 - 802.863.1202
>fax 802.863.7908
>
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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

877-SOLARVillage
413-256-6777,  Fax 413-825-0372
61 Baker Rd
Shutesbury, MA 01072

PO Box 115
Boonville, CA 95415
707-895-9015, Fax 707-897-0024
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