PV north facing in US [RE-wrenches]

[Bill Roush]

Just to further clutter up the debate I started, keep in mind that coal
plants aren't often placed for maximum efficient power delivery to the
consumer either, as they are located many miles and transmission
efficiency percentage points away from their end users. There are many
more examples we could site. This customer probably won't buy anything
here in the land of NO subsidies anyway, and if they do they will be
told what to expect of the systems production. I'll be lucky if they go
with a 'token' solar installation. If they still want to spend their
money that way, they are free to do so in the land of the free and the
home of the brave. I would still rather have people 'waste' money on a
good, but less than perfect solar installation than most of the things I
see money 'wasted' on. 

Best,
Bill Roush
Solar Electric Systems/KC, Inc.

  


-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com] 
Sent: Wednesday, July 23, 2003 11:51 PM
To: RE-wrenches at topica.com
Subject: RE: PV north facing in US [RE-wrenches]

Graham,

The thermal efficiency of a thermal collector goes to pot at low
irradiance
depending if the ambient temperature is low so there is some difference
to
the response of PV vs. Thermal at low irradiance. Off-angle irradiance
would
have a greater effect on a thermal collector and I think that is born
out in
the incident angle modifiers that are used in the performance models for
each.

To develop a valid performance model you have to take into account
irradiance, temperature, and incident angle modifier to get the answer.
You
also must validate that information against a real world installation.
There
are some very well validated models out there that do this stuff.

There are a lot more people that use various computer models without a
full
understanding of how they work (e.g. PVWATTS) and end up with ridiculous
results. Garbage in is, in fact, garbage out.

Mounting collectors on the north side of a very low pitch roof would
admittedly be a last resort, but I can't say that I would never do it. I
have seen plenty of people install systems that perform below 75% of
optimal
(like about half the systems in California if the truth were known). It
does
not justify bad performance, but many installations have far worse
performance than expected for a variety of reasons. The pictures you
posted
on your website are an excellent case in point.

The desire of that installer to get better performance by facing the
panels
to the south had a much worse effect than laying them in the roof
orientation--but the installer clearly had no idea--that's the scary
part
and why I will continue to teach basic PV courses to neophytes.

Bill.


-----Original Message-----
From: Graham Owen [mailto:graham at solarexpert.com]
Sent: Wednesday, July 23, 2003 5:41 PM
To: RE-wrenches at topica.com
Subject: RE: PV north facing in US [RE-wrenches]


Hi Doug, The street name was changed in Photoshop.

I would NEVER install a solar panel facing north in So Cal.  If you look
at the performance of solar water heaters on tract homes the water in
the north facing systems will be approximately the same as ambient, when
the south facing systems are HOT.  Maybe the photon absorption on PV
modules is completely different than thermal collectors, but as a solar
guy it seems wrong to install solar panels facing north.  Am I wrong?

Graham


-----Original Message-----
From: Doug Pratt [mailto:dmpratt at sbcglobal.net]
Sent: Wednesday, July 23, 2003 5:27 PM
To: RE-wrenches at topica.com
Subject: RE: PV north facing in US [RE-wrenches]


Is this wonderful example REALLY on "Total Eclipse Dr.", or did someone
Photoshop in that street sign?  Too cute... -Doug

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