[RE-wrenches] Using the North Facing Roof
Jason Szumlanski
jason at floridasolardesigngroup.com
Tue Jul 28 14:27:16 PDT 2015
This assumes 180º is optimum, which it may be for you, but 170º is actually
closer to modeled optimum in my area. Bill Brooks nailed it by clarifying
that it's all about the kWh/m^2/day, or more accurately kWh/m^2/year for
netmetered customers without TOU metering. My research at the link below
covers 36 azimuth at five popular roof pitches in my area (180 data
points). This is the analysis you need to do if you want really good
answers fro your customers, which is what Will has done below on a smaller
scale.
http://floridasolardesigngroup.com/solar-electricity-output-based-on-tilt-and-orientation/
If you are familiar with APIs, you can get the data from PVWATTS
programmatically without too much difficulty.
Jason Szumlanski
On Tue, Jul 28, 2015 at 2:23 PM, Will White <William.White at rgsenergy.com>
wrote:
> I did a quick simulation using PV Watts for a small system in Western
> Mass. Here’s what I found:
>
>
>
> Azimuth Roof Pitch kWH/year % of optimum
>
> 180 40
> 2593 100%
>
> 0 40
> 1291 49%
>
> 0 10
> 1996 79%
>
> 75 40
> 1829 70%
>
>
>
> Looks like roof pitch makes a pretty big difference in our area.
>
>
>
> Thanks,
>
> Will
>
>
>
> *Will White*
> Director of Construction – East Coast
>
> RGS Energy
>
> 64 Main St. |Montpelier, VT 05602
> tel 802.223.7804 | mobile 802.234.3167 | fax 802.223.8980
>
> *RGSEnergy.com <http://www.rgsenergy.com/> **|
> william.white at rgsenergy.com <william.white at rgsenergy.com> *
>
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>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Chris Mason
> *Sent:* Tuesday, July 28, 2015 1:50 PM
>
> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Subject:* Re: [RE-wrenches] Using the North Facing Roof
>
>
>
> In the Caribbean, low tilt roofs that face North can work very well, we
> (16 degrees) are below the Tropic of Cancer (23 degrees) and the sun is in
> the North for much of the year.
>
>
>
> On Tue, Jul 28, 2015 at 12:24 PM, <billbrooks7 at sbcglobal.net> wrote:
>
> Jarmo,
>
>
>
> The sun’s geometry is not nearly that simple. To understand the impact of
> north-facing arrays, you have to perform a simulation. PV:WATTS does this
> just fine and it is easy to show that a 18-degreed North-facing tilt
> produces 75% of a perfect 30-degree south-facing array. Far more than your
> assumption of 50%.
>
>
>
> To compare 15-degrees South to 15-degrees North, the numbers are slightly
> better at 77%. We are going to see a lot of north-facing arrays once people
> understand that low tilt angles are very forgiving on North slopes. Steep
> slopes are a totally different story and you have to run the numbers….
>
>
>
> Bill.
>
>
>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Jarmo.Venalainen at schneider-electric.com
> *Sent:* Tuesday, July 28, 2015 8:04 AM
> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Subject:* Re: [RE-wrenches] Using the North Facing Roof
>
>
>
> I did a slide on the effect of North facing modules. For even a fairly
> aggressive rotation North as shown, the effect is "only" a 50% reduction.
>
> The questions of whether or not to do it, are,
>
> - is the mounting structure simpler, lower cost
> - security against wind
> - can I put a larger array on the roof (typically yes, if you make back
> to back pyramid shaped structures)
> - overall, what is the cost versus benefit
>
> JARMO
>
> _____________________________________________________________________________________
>
> * Jarmo Venalainen* | * Schneider Electric | Xantrex Brand* |
> *CANADA* | *Sales Application Engineer*
> * Phone:* +604-422-2528 | * Tech Support:* 800-670-0707 | *Mobile:*
> +604-505-0291
> * Email:* jarmo.venalainen at schneider-electric.com | *Site:*
> www.Xantrex.com <http://www.xantrex.com/> | *Address:* 3700 Gilmore
> Way, Burnaby, BC V5G4M1
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> From:
>
> "Peter Parrish" <peter.parrish at calsolareng.com>
>
> To:
>
> "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>,
>
> Date:
>
> 07/28/2015 12:22 AM
>
> Subject:
>
> [RE-wrenches] Using the North Facing Roof
>
> Sent by:
>
> "RE-wrenches" <re-wrenches-bounces at lists.re-wrenches.org>
>
>
> ------------------------------
>
>
>
>
> 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
>
>
>
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> --
>
> Chris Mason
>
> NABCEP Certified Solar PV Installer™
>
> Solar Design Engineer
>
> Generac Generators Industrial technician
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