PV orientation [RE-wrenches]

[Bill Brooks]

Monseur Marco,

If the arrays are in California and the east-west subarrays are not wired in
series with each other, the east-west arrays will underperform the south
array by about 12% (0.88). In New York east-west would underperform south by
about 13% (0.85/0.98 = 0.87) since latitude is not exactly the best tilt
angle.

It is easy to see how even a small amount of shading on the south face could
cause you to look more seriously at the east or west faces. A separate
shading analysis should be done for each potential location before you can
diffinitively say that a given orientation is best.

The only way to get the data that Joe is looking for is to set up five
identical systems, side-by-side at east, south-east, south, south-west, and
west. Each inverter has to behave perfectly and no shading can be anywhere
on the horizon. That will yield a good test, but who is willing to do it?
You can also use a $50K multitracer from Daystar and put up to 15 or so
modules of the same type in whatever orientations you want. The Daystar will
operate the modules at max power and record the energy delivered for each
module. That would probably be the best--but who's going to pay for it?

I guess we have to trust our models for now and keep first things first.
Shading is a WAY bigger issue than orientation.

Bill.


-----Original Message-----
From: Mangelsdorf, Marco [mailto:mmangelsdorf at hei.com]
Sent: Thursday, August 22, 2002 1:35 PM
To: RE-wrenches at topica.com
Subject: SPAM: RE: PV orientation [RE-wrenches]


Massuh Bill and others,

Here's a teaser.  Let's look at two identically sized PV arrays.  One facing
due south at latitude.  The other one is split 50-50 due east and due west
at a slope of, say, 15-20 degrees.  Figure no shading issues for either
system along with clear sky insolation throughout the whole day.  I'd think
that the due south system would put out more solar kWhs over the course of
the year.  What would you estimate the percentage difference to be, on a
yearly basis, between these two systems?

marco
ProVision Technologies
Hilo, Hawai'i


These are orientation multipliers for the two states

For New York:

Direct./ oTilt	0o	15o	30o	45o	60o	90o
South			0.87	0.96	1.00	0.98	0.92	0.66
SE,SW			0.87	0.93	0.94	0.91	0.85	0.62
E,W			0.87	0.85	0.81	0.74	0.67	0.49


For California:

Direct./ oTilt	0o	15o	30o	45o	60o	90o
South			0.89	0.97	1.00	0.97	0.89	0.58
SSE,SSW		0.89	0.97	0.99	0.96	0.88	0.59
SE, SW		0.89	0.95	0.96	0.93	0.85	0.60
ESE,WSW		0.89	0.92	0.91	0.87	0.79	0.57
E, W			0.89	0.88	0.84	0.78	0.70	0.52

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