PV north facing in US [RE-wrenches]

Thu Jul 24 12:27:39 PDT 2003

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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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