PV north facing in US [RE-wrenches]

[Tom Rentz]

To continue on this thread, (Shady Boy -- good one!)
The Watt Sun tracker does a very good job tracking north/south/east/west, even works at artic circle locations, if you employ the dual tracker model. Of course, cost vs. payback must be calculated for the installation, and large array combinations could prove expensive. But we have one 1800W array (AZ 300) that we certainly are happy with!

Tom Rentz


Our office is powered by the sun and the wind! You can produce your own renewable energy!

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--- William Korthof <wkorthof at earthlink.net> wrote:

There's another variable to this north-facing equation, I think...

Another metric besides annual kWh is annual $$$$----for many
or most customers, $cost and $payback are the "bottom line".

PG&E offers TOU pricing, which is generally the best bet for
E-NET + PV customers. The E7 rate is great----summer peak
"sell" power is worth about 4 times as much as off-peak power.

Consider that a north-facing (or east or west) roof performs
similarly (kWh output) to a south roof in the summer months.
Also, a west roof puts out the most summer on-peak kWh.

So overall, for a PGE customer with E7, west-facing may be
a bit better economically than south, even though the annual
kWh output is 15-20% lower. North facing gets about as much
of the on-peak summer output as south, so even though the
winter output of north-facing approaches nil, the annual value
of north-facing solar arrays in PG&E might not be so bad.


/wk



At 12:57 PM 7/23/03 -0700, Bill Brooks wrote:
>Tom,
>
>I agree with your previous post about the north side of a 7:12 pitch (30
>degrees) being in the shade during the winter. However you are mistaken with
>the information below.
>
>I live in Vacaville and we get very little Tule fog since we are on the
>extreme edge of the Big Valley. Tule fog causes scatter such that it almost
>does not matter where your collectors point in the winter (north is almost
>as good as south--both are poor but that are not zero).
>
>Where are you getting your information? The sources of data for Tom Hoff's
>Clean Power Estimator and PVFCHART are backed up by good correlations to
>field performance. Where do you get the less than 50% number? --sounds like
>a suburban myth to me.
>
>People should not put systems in the shade on the south roof. My example was
>merely to stimulate the mind to find a location that is closest to south
>with the least amount of shade. For low-pitch roofs, that could be the north
>side as crazy as that sounds. The whole purpose is maximizing performance.
>Site performance is a function of two variables--orientation and shading.
>These factors need to be calculated separately and multiplied together to
>determine the overall effect.
>
>I was hoping someone would question my results. If you can produce good data
>that contradicts this analysis, I am more than happy to change my mind.
>
>Bill.
>
>
>-----Original Message-----
>From: Tom Lane, Energy Conservation Services
>[mailto:solar8 at ehostingbiz.com]
>Sent: Wednesday, July 23, 2003 12:08 PM
>To: RE-wrenches at topica.com
>Subject: Re: PV north facing in US [RE-wrenches]
>
>
>This is ridiculous a 4:12 pitch roof in Vacaville, CA will not produce
>50% of the solar gained from on a year round basis if you had clear
>skies every day.  The "Tule fog" in the Vacaville area results in almost
>0 gain no matter how you face solar panels during the winter.  Lurkers on
>this wrenches site will pick up the wrong impression.
>
>You have to take the microclimates into account if
>microclimates are not taken into account serious misinformation can get
>spread to people who do not understand the local situation.  In no cases,
>should people be encouraged to face solar panels north on a north facing
>roof above 30 degrees latitude with a 4:12 or steeper pitch.
>
>Gator Tom
>
>
>----- Original Message -----
>From: "Bill Brooks" <billb at endecon.com>
>To: <RE-wrenches at topica.com>
>Sent: Tuesday, July 22, 2003 6:41 PM
>Subject: RE: PV north facing in US [RE-wrenches]
>
>
>Bill and Joel,
>
>My SPAM filter caught this because it said north facing PV in the US (not
>really). However, Joel asks a good question and there is very good answer.
>
>Case in point. A homeowner has a south-facing house with a 4:12 roof pitch
>(18 degrees). The detailed version of Clean-Power Estimator works for a
>North facing array. In Vacaville (Northern California) the north roof face
>will produce 75% of the south face on an annual basis. Now consider a short
>and fat tree on the south side that provides lovely shade to the house and
>south roof, but leaves the north roof unshaded. The Pathfinder shows that
>the tree limits performance by 40% on an annual basis.
>
>Question: Which location will produce more energy?
>Answer: North face (and we're not in New Zealand!)
>
>Of course system performance could be improved by going flat or tilted on
>tilt legs to the south, but the owner may think that is ugly (and they would
>be right).
>
>As long as you and the customer know the impact of the decision, go for it.
>
>Bill.
>
>
>-----Original Message-----
>From: Bill Roush [mailto:solarguide at everestkc.net]
>Sent: Tuesday, July 22, 2003 1:50 PM
>To: RE-wrenches at topica.com
>Subject: RE: PV north facing in US [RE-wrenches]
>
>
>Why North facing? I will never speak ill of a client, they are so rare
>in these parts, so my lips are sealed.
>
>Best,
>Bill Roush
>Solar Electric Systems/KC, Inc.
>
>
>
>
>-----Original Message-----
>From: Joel Davidson [mailto:joeldavidson at earthlink.net]
>Sent: Monday, July 21, 2003 9:17 PM
>To: RE-wrenches at topica.com
>Subject: Re: PV north facing in US [RE-wrenches]
>
>Bill,
>You can input north-facing azimuths in PVWATTS
>http://rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/text_only.html
>I've heard about north-facing arrays in Hawaii because the islands are
>so
>close to the equator and I saw a grid-connected 25 kW array in India
>that is
>manually tilted north and south depending on the season. But PV on a
>north-facing roof in the U.S.? Why?
>Best,
>Joel Davidson
>
>Bill Roush wrote:
>
> > I am not finding the references I see periodically to de-rating for a
> > north facing roof in the US. Any links for me?
> >
> > Best,
> > Bill Roush
> >
> >
> >
> >
> >
>
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