[RE-wrenches] Using the North Facing Roof

Chris Mason cometenergysystems at gmail.com
Thu Jul 30 14:42:46 PDT 2015


Could you add the ability to use coordinates instead of zip code, otherwise
it is no use outside the US.

On Thu, Jul 30, 2015 at 1:16 PM, Jason Szumlanski <
jason at floridasolardesigngroup.com> wrote:

> I figured while I'm at it I might as well release something else that you
> can actually print out and present to your clients or use for your own
> visualization purposes. This is a very similar tool that will output a web
> page with a radar chart (like a spider web representing the compass) and a
> data table down to the secondary intercardinal directions. Hover over the
> points to see the value.
>
> http://floridasolardesigngroup.com/pva/do-site-analysis.php
>
> Run it at two different tilt angles and check out the differences.
> Eventually I plan to update this to compare two (or more) tilt angles on
> the same radar chart. For now, this is all you get. :)
>
>
> [image: Inline image 3]
>
>
>
> Once again, enjoy!
>
> Jason
>
>
>
> On Wed, Jul 29, 2015 at 10:56 AM, Jason Szumlanski <
> jason at floridasolardesigngroup.com> wrote:
>
>> I want to give back to this forum that has been so valuable to me, so
>> here it is... a tool for you to quickly compile data for multiple compass
>> orientations for a given pitch...
>>
>> http://floridasolardesigngroup.com/pva/do-pvwatts-wrenches.php
>>
>> This PVWATTS derived tool will give you 36 data points for solar energy
>> production with every azimuth from 0º to 350º at 10º increments for a given
>> location and pitch. You can enter your desired system size to model its
>> output and include your desired PVWATTS derate (system loss) factor. It
>> will download a .CSV file each time you run the tool. You can run it for a
>> variety of tilt angles based on your needs to compile data for your own
>> study.
>>
>> There are limits on use, but if everyone does not run out and use it at
>> the same time it should be fine.
>>
>> Once you get your data into a spreadsheet you can easily slice and dice
>> it any way you want and make some great visualizations.
>>
>> [image: Inline image 1]
>>
>>
>> Enjoy!
>>
>> Jason Szumlanski
>>
>>
>>
>>
>>
>> On Tue, Jul 28, 2015 at 7:01 PM, Allan Sindelar <allan at sindelarsolar.com>
>> wrote:
>>
>>> I am paying close attention to this thread, but for different reasons. I
>>> have designed and will install next month an off grid system for a
>>> high-elevation research hut. At 14,242' I believe this will be the highest
>>> elevation off grid system in the continental US (Alaska too?), at the
>>> Summit Hut atop White Mountain, east of the Sierra crest in eastern
>>> California (wmrc.edu/facilities/bar/summit.html). For me it's sort of a
>>> post-retirement summer working adventure. A nearly identical system will
>>> serve an older observatory at 12,700' in the same area. The Summit Hut will
>>> get a roof array where winds of 190 mph have been measured, I'm told. The
>>> roof has about a 5º north-facing tilt.
>>>
>>> I'm old-school too, thinking in terms of a 25º tilt to south. But other
>>> than powering an internet repeater all year, the system is only used during
>>> the summer months, mid-June to mid-October, when the snow has melted and
>>> it's accessible by a long jeep trail. So in that respect it's similar to a
>>> flat- or north-facing array in a grid-tied system, where only summer gain
>>> matters much and a southern tilt matters less that I want to believe.
>>> Jason's chart is pretty useful here, suggesting that I should pay more
>>> attention to handling wind loads with a low angle than maximizing summer
>>> gain.
>>> Allan
>>>
>>> *Allan Sindelar*
>>> <allan at sindelarsolar.com>allan at sindelarsolar.com
>>> NABCEP Certified PV Installation Professional
>>> NABCEP Certified Technical Sales Professional
>>> New Mexico EE98J Journeyman Electrician
>>> Founder (Retired), Positive Energy, Inc.
>>> *505 780-2738 <505%20780-2738> cell*
>>>
>>>
>>> On 7/28/2015 11:15 AM, billbrooks7 at sbcglobal.net wrote:
>>>
>>> Larry and Peter,
>>>
>>>
>>>
>>> You are too old-school to think outside the box. It’s not about direct
>>> sunlight—it’s all about kWh/m^2/day and those numbers don’t lie. Your
>>> analysis is not correct and this is why simple analyses will always give
>>> you a wrong answer.
>>>
>>>
>>>
>>> North-facing arrays have been financially attractive for years, but many
>>> have not done it due to taboos or bad analysis. Reverse-tilt arrays often
>>> look horrible and should be avoided particularly on the street-side of a
>>> house. Also, the structural impacts of tilted arrays on residential
>>> rooftops are not well-understood so wind-loading calculations are complex
>>> at best.
>>>
>>>
>>>
>>> We have been using east and west facing roofs for your years so what’s
>>> the big deal about north? I put together the one of the first tables of
>>> orientation version performance way back in 2001 for the California Energy
>>> Commission to combat the misconceptions that PV arrays had to be mounted at
>>> 45-degrees facing South (the prevailing misconception at the time). I
>>> didn’t print the North facing numbers because the concept would have blown
>>> people’s minds at the time—they weren’t ready for the truth.
>>>
>>>
>>>
>>> 30-degrees facing south is optimal in most latitudes from 20-degrees to
>>> 50-degrees. (perfect in most locations)
>>>
>>> 4:12 pitch (18-degrees) facing south is 97% of perfect.
>>>
>>> 4:12 pitch east or west is 88% of perfect.
>>>
>>> Flat is 89% of perfect.
>>>
>>> 4:12 pitch facing north is 75% of perfect.
>>>
>>>
>>>
>>> The truth shall set you FREE.
>>>
>>>
>>>
>>> Bill.
>>>
>>>
>>>
>>>
>>>
>>> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org
>>> <re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *Starlight
>>> Solar Power Systems
>>> *Sent:* Tuesday, July 28, 2015 9:41 AM
>>> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
>>> <re-wrenches at lists.re-wrenches.org>
>>> *Subject:* Re: [RE-wrenches] Using the North Facing Roof
>>>
>>>
>>>
>>> In Yuma, AZ, north facing modules will have direct sunlight for small
>>> part of the year. In the picture, look at the yellow area above the
>>> East-West line. Thats direct sunlight from the north. The green top line in
>>> the picture shows summer solstice showing sunlight from sunrise to about
>>> 0930 and from 1530 to sunset. The energy harvested during those hours will
>>> be tiny compared to the peak sun hours on the south side. The angle of
>>> incidence will also reduce the total power generated during those hours.
>>>
>>>
>>>
>>> The thin brown middle line is the equinox. By then, there is no direct
>>> sunlight on the north side. I can not see any benefit in AZ even at todays
>>> low prices. Now, if I were building in Quetzaltenango, Guatemala, that
>>> would be a different story. But then again, I would have to clean off the
>>> volcanic ash each morning.
>>>
>>>
>>>
>>> Larry Crutcher
>>> Starlight Solar Power Systems
>>>
>>>
>>>
>>> chart came from http://www.gaisma.com/en/
>>>
>>>
>>>
>>>
>>>
>>> On Jul 27, 2015, at 11:21 PM, Peter Parrish <
>>> peter.parrish at calsolareng.com> wrote:
>>>
>>>
>>>
>>> I recently read a short piece that caught me up short, and I quote:
>>>
>>>
>>> “The fast dropping cost of solar, while a huge boon to the adoption of
>>> solar PV, has counter-intuitively altered design parameters. No longer is
>>> the north-facing roof considered unusable because limited application in
>>> less-than optimal orientations can still show a positive net benefit.
>>> Arrays are thus designed now with elements or sub-arrays in these
>>> locations, increasing overall kW installation while reducing the energy
>>> production per capacity installed. This might have been anticipated based
>>> on sheer economic analysis from a users perspective, but so long has solar
>>> been expensive that these less optimal orientations were never seriously
>>> considered.”
>>>
>>>
>>>
>>> I doubt that the individual who wrote this piece came to these
>>> conclusions him/herself. Does anyone know of a recent article that argued
>>> this perspective? Is this an emerging design practice? If so, I’d like to
>>> know more about it.
>>>
>>>
>>>
>>> -          Peter
>>>
>>>
>>>
>>> Peter T. Parrish, Ph.D.
>>>
>>> President, SolarGnosis
>>>
>>> 1107 Fair Oaks Ave., Suite 351
>>>
>>> South Pasadena, CA 91030
>>>
>>> (323) 839-6108
>>>
>>> <petertor at pobox.com>petertor at pobox.com
>>>
>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>>
>
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-- 
Chris Mason
NABCEP Certified Solar PV Installer™
Solar Design Engineer
Generac Generators Industrial technician

www.cometsolar.com <http://www.cometenergysystems.com>
264.235.5670
869.662.5670
Skype: netconcepts
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