Unisolar Roofing [RE-wrenches]

Bill Brooks billbrooks7 at earthlink.net
Wed Mar 14 15:47:44 PST 2001


I realize that ASCII can be cruel, but hopefully you can read this. This is
top secret so make sure you spread it around ;-). This chart tells us the
impact of fixed orientation on annual energy production for a
grid-connected, net-metered PV system. Do not use this for off-grid since we
cannot predict array utilization nearly as well. The interesting thing about
this chart is that it clearly shows that annual energy producting is not
very sensitive to fairly wide variations in orientation (4:12 to 12:12, SE
to SW only has about 5% loss from ideal). Moral of the story is don't tilt
your modules on rooftop PV systems because it looks like hell, costs more to
install, and often doesn't buy much as far as performance.


Roof pitch	Flat	4:12	7:12	12:12	21:12	Vertical
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



Okay all you Wrenches out there, on the chart below are some real-life
numbers you should be using for grid-connect PV systems that are properly
oriented. This should generate some good controversy because nobody I know
states numbers this low. However, these are real-life conservative numbers.
A well installed system with minimal shading should be able to consistently
produce this much electricity or more in a year. If it doesn't, there is
something wrong with it (equipment or installation). The new California
Buydown guidelines require a meter come June 1, 2001, so sharpen your pencil
because customers are now going to need energy estimates. This means you
need to do a detailed shading analysis with a Solar Pathfinder, use the
chart above to adjust for orientation, and multiply that number by your
location below and you're done! Piece of cake.

CITY			kWh/kWstc
Arcata		1092
Shasta		1345
San Francisco	1379
Sacramento		1455
Fresno		1505
Santa Maria		1422
Barstow		1646
Los Angeles		1406
San Diego		1406


Anybody want to comment?

Bill.

> -----Original Message-----
> From: William Miller [mailto:wrmiller at slonet.org]
> Sent: Wednesday, March 14, 2001 2:13 PM
> To: RE-wrenches at topica.com
> Subject: RE: Unisolar Roofing [RE-wrenches]
>
>
> Bill:
>
> I am located in San Luis Obispo County.  I have a client that
> installed his
> own ground mount array at 210 deg. true.  I need to know in this type of
> situation, how much reduction in output will they have?  I would like to
> own software that can determine this as it comes up frequently.
>
> William
>
>
>
> At 09:40 AM 3/14/01 -0800, you wrote:
> >Where are you located. I have a chart for the state of California. It
> >doesn't necessarily work in other locations. A similar chart was done for
> >Colorado. It's just a series of PVFCHART simulations--works great.
> >
> >Bill.
> >
>
>
> __________________________________________________________________
> William Miller
> SLO Communications: Communications and Power Systems Consulting
> PO Box 50, Santa Margarita, CA 93453
> Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
> email: wrmiller at slonet.org
> License No. C-10-773985
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