utility line shadows [RE-wrenches]

[Jason Fisher]

EH has a good idea about direct measurement at the site. I would add that it
all depends on how the shading hits the strings. Assuming that the bypass
diodes are working properly, a passing shadow line across a module might not
present too much of an impact if the string's voltage remains well within
the inverter's tracking window as it might only shut down 18 cells at a
time. This assumes that the shadow will only be on a module or two in any
one string at a time. If the shadow falls across many modules in the string
at the same time, it could push the voltage way down, possibly out of range
of the inverter. The high voltage inverters give us a lot more play room
than we used to have when talking about partial shading, particularly if
each string is tracked independently or on a dedicated inverter.

Jason Fisher

Aurora Energy LLC
P.O.Box 3315
Annapolis, MD 21403

voice 410-268-3088 / fax: 410-268-3684
email: jason at aurora-energy.com


-----Original Message-----
From: EH Roy [mailto:ehroy at solar-works.com]
Sent: Thursday, August 28, 2003 11:21 AM
To: RE-wrenches at topica.com
Subject: RE: utility line shadows [RE-wrenches]

Andy,

I had a utility line shadow over one of several 400V series strings of
multicrystalline modules a few years ago. I could easily detect the lower
output of that string when the sun was positioned to cast a shadow over it.
It was right up with other string outputs when the shadow was not there. I
can't give you anything quantitative, it was too long ago - it was
noticeable but it did not totally eliminate the output of that string by any
means.

If you want something quantitative, you might hold one of the modules you
plan to use at the design tilt angle and measure the Isc with and without a
utility line shadow on it to get a percent output loss. Combine that with
some pathfinder analysis of your proposed array site to determine how many
series strings of the array will have utility line shading and when.

Hope that is helpful.

E. H. Roy
Solar Works Inc.
64 Main Street
Montpelier, VT 05602
802 223-7804 x306
ehroy at solar-works.com


-----Original Message-----
From: Andy Cochrane [mailto:andy at powertripenergy.com]
Sent: Wednesday, August 27, 2003 8:41 PM
To: RE-wrenches at topica.com
Subject: utility line shadows [RE-wrenches]


Hi all,

I'm looking at a potential array location that has excellent solar
exposure EXCEPT for those 4 or 5 nasty utility lines about 20 feet up.
They cast a thin and diffuse shadow on the ground, but I wonder if this
will be enough of a shadow to limit the production from Sharp
multi-crystalline panels mounted on a 10 foot high roof?

Anybody have experience with this?

Andy Cochrane
andy at powertripenergy.com

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