Re: [RE-wrenches] Using the North Facing Roof
Jarmo, Your intent was laudable, but simple trigonometry just flat out fails with the complexity of solar geometry. PVWatts is so easy to use that anyone, without any knowledge of trigonometry, can use it with far more accurate results. Take advantage of nice, free software that your tax dollar paid for many years ago. Your harvest calculations don’t take into account about 20 factors that impact solar energy on a PV array. You are only looking at instantaneous sunlight at noon on a south-facing surface. There is almost nothing that we can learn from that simple of an analysis which is why we turned to simulations over 25 years ago. I have all my complex geometry sun position equations from the solar class I took in 1985, but to calculate energy from those equations requires hourly weather data and a computer—no other method will work. PVWatts does this. Use PVWatts and continue to advocate the installation of PV modules wherever they make economic sense—north, south, east, or west. Bill. From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Friday, July 31, 2015 3:53 PM To: RE-wrenches re-wrenches@lists.re-wrenches.org Subject: Re: [RE-wrenches] Using the North Facing Roof Hi: I went over and looked at my calculations whereby I arrived at the simple expression that the change in harvested solar energy is bounded by the sin of the angle of tilt to the North. As I was doing it however, it became clear that the reason this simple result popped up, is simply because, 1. The effect of tilting an array North is exactly the same as if the system was physically relocated farther North by that amount of degrees latitude. 2. There is a linearly decreasing amount of annual insolation which is a linear function of latitude. Latitude versus Average Annual Insolation 30 degrees latitude has 8.7 kWh-m2 40 degrees latitude has 7.8 kWh-m2 50 degrees latitude has 6.7 kWh-m2 60 degrees latitude has 5.6 kWh-m2 3. The SIN function is very linear for small angles up to about 40 degrees Angle versus sin sin(10) = 0.17 sin(20) = 0.34 sin(30) = 0.5 sin(40) = 0.64 The sin expression describing the effect of north tilt is a bounding function, whereby it bounds the maximum reduction in energy harvest as a function of tilt. It is a bounding analysis as it does not take into account the effect of atmospheric diffuse radiation which has the effect of making the tilt loss less than it would be if the earth had no atmosphere. For example if an array was tilted north by 40 degrees in Vancouver, with no atmosphere the modules would see no sunlight for 6 months of the year. With an atmosphere, there is still a lot of light to be gathered. Regardless, my intent with the exercise from the beginning was to find a bound for the potential loss effect of North tilt so that I could continue to advocate the maximum use of roof space even when that roof is North facing. 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: mailto:jarmo.venalai...@schneider-electric.com jarmo.venalai...@schneider-electric.com | Site: http://www.xantrex.com/ www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: billbroo...@sbcglobal.net mailto:billbroo...@sbcglobal.net To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org mailto:re-wrenches@lists.re-wrenches.org , Date: 07/28/2015 12:20 PM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org mailto:re-wrenches-boun...@lists.re-wrenches.org _ Jarmo, Unfortunately, simple is wrong in this case—and detrimental to the PV industry that needs all the roof real estate it can find. Bill. Bill Brooks, PE Principal Brooks Engineering From: RE-wrenches [ mailto:re-wrenches-boun...@lists.re-wrenches.org mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com mailto:jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 10:43 AM To: RE-wrenches re-wrenches@lists.re-wrenches.org mailto:re-wrenches@lists.re-wrenches.org Subject: Re: [RE-wrenches] Using the North Facing Roof Hi: Granted that the description is very simple, but that is the intent. The essence of it is that the loss for small variations in angle of incidence is approximately bounded by, (less than), the sin of the angle between the orientations of two panels/arrays in question. 10 degrees --- minus 17% 20 degrees --- minus 33% 30 degrees --- minus 50% If you go through the detailed math and take into account atmospheric effects
Re: [RE-wrenches] Using the North Facing Roof
Hi: I went over and looked at my calculations whereby I arrived at the simple expression that the change in harvested solar energy is bounded by the sin of the angle of tilt to the North. As I was doing it however, it became clear that the reason this simple result popped up, is simply because, 1. The effect of tilting an array North is exactly the same as if the system was physically relocated farther North by that amount of degrees latitude. 2. There is a linearly decreasing amount of annual insolation which is a linear function of latitude. Latitude versus Average Annual Insolation 30 degrees latitude has 8.7 kWh-m2 40 degrees latitude has 7.8 kWh-m2 50 degrees latitude has 6.7 kWh-m2 60 degrees latitude has 5.6 kWh-m2 3. The SIN function is very linear for small angles up to about 40 degrees Angle versus sin sin(10) = 0.17 sin(20) = 0.34 sin(30) = 0.5 sin(40) = 0.64 The sin expression describing the effect of north tilt is a bounding function, whereby it bounds the maximum reduction in energy harvest as a function of tilt. It is a bounding analysis as it does not take into account the effect of atmospheric diffuse radiation which has the effect of making the tilt loss less than it would be if the earth had no atmosphere. For example if an array was tilted north by 40 degrees in Vancouver, with no atmosphere the modules would see no sunlight for 6 months of the year. With an atmosphere, there is still a lot of light to be gathered. Regardless, my intent with the exercise from the beginning was to find a bound for the potential loss effect of North tilt so that I could continue to advocate the maximum use of roof space even when that roof is North facing. 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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: billbroo...@sbcglobal.net To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org, Date: 07/28/2015 12:20 PM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org Jarmo, Unfortunately, simple is wrong in this case—and detrimental to the PV industry that needs all the roof real estate it can find. Bill. Bill Brooks, PE Principal Brooks Engineering From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 10:43 AM To: RE-wrenches re-wrenches@lists.re-wrenches.org Subject: Re: [RE-wrenches] Using the North Facing Roof Hi: Granted that the description is very simple, but that is the intent. The essence of it is that the loss for small variations in angle of incidence is approximately bounded by, (less than), the sin of the angle between the orientations of two panels/arrays in question. 10 degrees --- minus 17% 20 degrees --- minus 33% 30 degrees --- minus 50% If you go through the detailed math and take into account atmospheric effects, especially when the sun is near the horizons, temperature, location, weather, etc., the result will vary, but will not be worse than the sin of the angle. I'll draw out better picture with more detail for Vancouver. We're at a fairly high latitude, so overall array orientation is a more sensitive factor than farther south. 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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Brian Mehalic br...@solarenergy.org To: RE-wrenches re-wrenches@lists.re-wrenches.org, Date: 07/28/2015 09:48 AM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org The analysis of 50% of south facing production is too simplistic; running some modeling shows that, depending on the latitude, the difference can be much smaller, approaching 25% less for the north facing. I think this layout could become more common especially on low slope commercial roofs, where the north facing module would occupy space that was already unused due to interrow shading. Of course the closer to the equator the less difference between production of the north and south arrays...and you better be careful when stringing them in series so
Re: [RE-wrenches] Using the North Facing Roof
Chris, Just enter the address as lat,long with negative for south or west. For example, USVI: 18.3500,-64.9333 Leave the city, state, zip blank. No spaces. Let me know if that doesn't work. It's going to pick the closest TMY3 weather station. Jason On Thu, Jul 30, 2015 at 5:42 PM, Chris Mason cometenergysyst...@gmail.com wrote: 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 ja...@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. :) Once again, enjoy! Jason On Wed, Jul 29, 2015 at 10:56 AM, Jason Szumlanski ja...@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. Enjoy! Jason Szumlanski On Tue, Jul 28, 2015 at 7:01 PM, Allan Sindelar al...@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* ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
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 al...@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* al...@sindelarsolar.comal...@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, billbroo...@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-boun...@lists.re-wrenches.org re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Starlight Solar Power Systems *Sent:* Tuesday, July 28, 2015 9:41 AM *To:* RE-wrenches re-wrenches@lists.re-wrenches.org re-wrenches@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
[RE-wrenches] Using the North Facing Roof
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 peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
WrenchesI see this working south of the tropic of cancer but at 1000 watts per meter squared tilted north might work for a month a year but I don't think the tax credits were proposed for poor performance module installations. I see enphase annual readings prove the point. Jerry Sent from my Verizon Wireless 4G LTE smartphone Original message From: Peter Parrish peter.parr...@calsolareng.com Date: 07/27/2015 7:21 PM (GMT-10:00) To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org Subject: [RE-wrenches] Using the North Facing Roof 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, SolarGnosis1107 Fair Oaks Ave., Suite 351South Pasadena, CA 91030(323) 839-6108peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
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 al...@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 cell On 7/28/2015 11:15 AM, billbroo...@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-boun...@lists.re-wrenches.org] On Behalf Of Starlight Solar Power Systems Sent: Tuesday, July 28, 2015 9:41 AM To: RE-wrenches re-wrenches@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
Re: [RE-wrenches] Using the North Facing Roof
Within the last year a fairly large (~100-130kW?) system was installed on a 4-sided building in Alberta that had PV installed on all four vertical walls. Each side's PV system operating independently, of course. We were not involved in this project and i'm not totally up to speed on the why's, how's and expected productions and so on... but i know the designer and i'm pretty sure he already has a good idea what range the production output of each different facing wall will fall in. I can inquire if he has any articles or insight he would be willing to share with this group. *Benn Kilburn * CSA Certified Solar Photovoltaic Systems Electrician, SkyFire Energy Inc 6706 – 82 Ave NW | Edmonton, AB | T6B 0E7 P: 780-474-8992 | F: 888-405-5843 | www.skyfireenergy.com [image: email] b...@skyfireenergy.com [image: facebook] https://www.facebook.com/SkyFireEnergy [image: twitter] https://twitter.com/SkyFireEnergy [image: linkedin] https://www.linkedin.com/company/283735?trk=tyahtrkInfo=tarId%3A1408655033432%2Ctas%3Askyfire%2Cidx%3A2-2-5 [image: google] https://plus.google.com/+SkyFireEnergy/ [image: SkyFire Energy Logo_horizontal] On Mon, Jul 27, 2015 at 11:21 PM, Peter Parrish peter.parr...@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 peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
I think the point of view Peter shared has more to do with lower sloped North facing or other non-ideal orientations. The proof is in the pudding – just simulate the production and utility bill offset and see if the proposed orientation makes sense financially. We haven’t done any North facing arrays (yet?) but we have a few that are North-West in orientation and they are working as projected. I think a side question that this poses is whether, for example, it makes sense to install a reverse tilt on a North facing roof or just mount the panels flush and install more of them. My calculations show that the reverse tilt is still a better economical choice but it is no longer as cut and dry as it once was when modules were more expensive. Of course reverse tilt arrays pose structural engineering and aesthetic considerations so we really try to shy away from them. Best, August *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *jerrysgarage01 *Sent:* Tuesday, July 28, 2015 12:29 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Using the North Facing Roof Wrenches I see this working south of the tropic of cancer but at 1000 watts per meter squared tilted north might work for a month a year but I don't think the tax credits were proposed for poor performance module installations. I see enphase annual readings prove the point. Jerry Sent from my Verizon Wireless 4G LTE smartphone Original message From: Peter Parrish peter.parr...@calsolareng.com Date: 07/27/2015 7:21 PM (GMT-10:00) To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org Subject: [RE-wrenches] Using the North Facing Roof 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 peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
We get this question all the time, mostly due to aesthetic concerns. The location is obviously a huge factor in this decision, but the mounting pitch is also very important. I did a PVWATTS-based study recently based on our local area, and the results are here: http://floridasolardesigngroup.com/solar-electricity-output-based-on-tilt-and-orientation/ Other related resources: http://floridasolardesigngroup.com/pitch-solar-panels-on-my-roof-is-it-necessary/ http://floridasolardesigngroup.com/can-i-put-solar-panels-on-my-north-roof-in-southwest-florida/ The bottom line is that the marginal cost of adding solar panels to a north roof may be completely viable in some scenarios, and even a completely north facing array in others. It often depends on the investment requirements of the buyer. I can see benefits to off-grid systems, too, where production on even a north vertical wall can provide critical power at certain times of day at certain latitudes. If aligning production with consumption is important in a situation, every pitch and azimuth is on the table for analysis. Jason Szumlanski Florida Solar Design Group On Tue, Jul 28, 2015 at 1:21 AM, Peter Parrish peter.parr...@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 peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@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-boun...@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 peter...@pobox.com __ This email has been scanned by the Symantec Email Security.cloud service. __ ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
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-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 8:04 AM To: RE-wrenches re-wrenches@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: mailto:jarmo.venalai...@schneider-electric.com jarmo.venalai...@schneider-electric.com | Site: http://www.xantrex.com/ www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ http://www.xantrex.com/ https://www.facebook.com/Xantrex https://twitter.com/Xantrex https://twitter.com/Xantrex *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com mailto:peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org mailto:re-wrenches@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-boun...@lists.re-wrenches.org mailto:re-wrenches-boun...@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 peter...@pobox.com mailto:peter...@pobox.com __ This email has been scanned by the Symantec Email Security.cloud service. _ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant
Re: [RE-wrenches] Using the North Facing Roof
The analysis of 50% of south facing production is too simplistic; running some modeling shows that, depending on the latitude, the difference can be much smaller, approaching 25% less for the north facing. I think this layout could become more common especially on low slope commercial roofs, where the north facing module would occupy space that was already unused due to interrow shading. Of course the closer to the equator the less difference between production of the north and south arrays...and you better be careful when stringing them in series so as not to mix N and S facing..plus filling in all those gaps between rows could make servicing the array a bit problematic! Cheers, Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org On Tue, Jul 28, 2015 at 10:24 AM, billbroo...@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-boun...@lists.re-wrenches.org] *On Behalf Of *jarmo.venalai...@schneider-electric.com *Sent:* Tuesday, July 28, 2015 8:04 AM *To:* RE-wrenches re-wrenches@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.venalai...@schneider-electric.com | *Site:* www.Xantrex.com http://www.xantrex.com/ | *Address:* 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ http://www.xantrex.com/ https://www.facebook.com/Xantrex https://twitter.com/Xantrex https://twitter.com/Xantrex *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@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-boun...@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 peter...@pobox.com __ This email has been scanned by the Symantec Email Security.cloud service. __ ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette
Re: [RE-wrenches] Using the North Facing Roof
Maybe I'm a bit slow, but I don't understand this slide at all. This might make sense for expected momentary power output at a particular static sun position (perpendicular to the south panel face) under test conditions, but it doesn't relate to real world energy output with weather and sun position throughout each day relative to the panels. Can you explain further what this slide is intended to show? Jason On Tue, Jul 28, 2015 at 11:03 AM, jarmo.venalai...@schneider-electric.com wrote: 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.venalai...@schneider-electric.com* jarmo.venalai...@schneider-electric.com | *Site:** www.Xantrex.com* http://www.xantrex.com/ | *Address:* 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ http://www.xantrex.com/ https://www.facebook.com/Xantrex https://twitter.com/Xantrex https://twitter.com/Xantrex *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@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-boun...@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 peter...@pobox.com ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
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.parr...@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 peter...@pobox.com ___ ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
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.comhttp://www.rgsenergy.com/ | william.wh...@rgsenergy.commailto:william.wh...@rgsenergy.com Confidentiality Note: This e-mail message may contain confidential or legally privileged information and is intended only for the use of the intended recipient(s). Any unauthorized disclosure, dissemination, distribution, copying or the taking of any action in reliance on the information herein is prohibited. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, or contain viruses. Anyone who communicates with us by e-mail is deemed to have accepted these risks. RGS Energy is not responsible for errors or omissions in this message and denies any responsibility for any damage arising from the use of e-mail. Any opinion and other statement contained in this message and any attachment are solely those of the author and do not necessarily represent those of the company. From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Chris Mason Sent: Tuesday, July 28, 2015 1:50 PM To: RE-wrenches re-wrenches@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, billbroo...@sbcglobal.netmailto:billbroo...@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-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.commailto:jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 8:04 AM To: RE-wrenches re-wrenches@lists.re-wrenches.orgmailto:re-wrenches@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 [cid:image001.gif@01D0C941.007047C0] JARMO _ Jarmo Venalainen | Schneider Electric | Xantrex Brand | CANADA | Sales Application Engineer Phone: +604-422-2528tel:%2B604-422-2528 | Tech Support: 800-670-0707tel:800-670-0707 | Mobile: +604-505-0291tel:%2B604-505-0291 Email: jarmo.venalai...@schneider-electric.commailto:jarmo.venalai...@schneider-electric.com | Site: www.Xantrex.comhttp://www.xantrex.com/ | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ [cid:image003.gif@01D0C941.007047C0]http://www.xantrex.com/ [cid:image004.gif@01D0C941.007047C0]https://www.facebook.com/Xantrex [cid:image005.gif@01D0C941.007047C0]https://twitter.com/Xantrex [cid:image006.gif@01D0C941.007047C0]https://twitter.com/Xantrex *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.commailto:peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@lists.re-wrenches.orgmailto:re-wrenches@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-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
Hi: Granted that the description is very simple, but that is the intent. The essence of it is that the loss for small variations in angle of incidence is approximately bounded by, (less than), the sin of the angle between the orientations of two panels/arrays in question. 10 degrees --- minus 17% 20 degrees --- minus 33% 30 degrees --- minus 50% If you go through the detailed math and take into account atmospheric effects, especially when the sun is near the horizons, temperature, location, weather, etc., the result will vary, but will not be worse than the sin of the angle. I'll draw out better picture with more detail for Vancouver. We're at a fairly high latitude, so overall array orientation is a more sensitive factor than farther south. 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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Brian Mehalic br...@solarenergy.org To: RE-wrenches re-wrenches@lists.re-wrenches.org, Date: 07/28/2015 09:48 AM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org The analysis of 50% of south facing production is too simplistic; running some modeling shows that, depending on the latitude, the difference can be much smaller, approaching 25% less for the north facing. I think this layout could become more common especially on low slope commercial roofs, where the north facing module would occupy space that was already unused due to interrow shading. Of course the closer to the equator the less difference between production of the north and south arrays...and you better be careful when stringing them in series so as not to mix N and S facing..plus filling in all those gaps between rows could make servicing the array a bit problematic! Cheers, Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org On Tue, Jul 28, 2015 at 10:24 AM, billbroo...@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-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 8:04 AM To: RE-wrenches re-wrenches@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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@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-boun...@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
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, billbroo...@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-boun...@lists.re-wrenches.org] *On Behalf Of *jarmo.venalai...@schneider-electric.com *Sent:* Tuesday, July 28, 2015 8:04 AM *To:* RE-wrenches re-wrenches@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.venalai...@schneider-electric.com | *Site:* www.Xantrex.com http://www.xantrex.com/ | *Address:* 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ http://www.xantrex.com/ https://www.facebook.com/Xantrex https://twitter.com/Xantrex https://twitter.com/Xantrex *** Please consider the environment before printing this e-mail From: Peter Parrish peter.parr...@calsolareng.com To: 'RE-wrenches' re-wrenches@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-boun...@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 peter...@pobox.com __ This email has been scanned by the Symantec Email Security.cloud service. __ ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- [image: Avast logo] https://www.avast.com/antivirus This email has been checked for viruses by Avast antivirus software. www.avast.com https://www.avast.com/antivirus ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re
Re: [RE-wrenches] Using the North Facing Roof
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-boun...@lists.re-wrenches.org] On Behalf Of Starlight Solar Power Systems Sent: Tuesday, July 28, 2015 9:41 AM To: RE-wrenches re-wrenches@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.parr...@calsolareng.com mailto:peter.parr...@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 peter...@pobox.com mailto:peter...@pobox.com ___ --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Using the North Facing Roof
Jarmo, Unfortunately, simple is wrong in this case—and detrimental to the PV industry that needs all the roof real estate it can find. Bill. Bill Brooks, PE Principal Brooks Engineering From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 10:43 AM To: RE-wrenches re-wrenches@lists.re-wrenches.org Subject: Re: [RE-wrenches] Using the North Facing Roof Hi: Granted that the description is very simple, but that is the intent. The essence of it is that the loss for small variations in angle of incidence is approximately bounded by, (less than), the sin of the angle between the orientations of two panels/arrays in question. 10 degrees --- minus 17% 20 degrees --- minus 33% 30 degrees --- minus 50% If you go through the detailed math and take into account atmospheric effects, especially when the sun is near the horizons, temperature, location, weather, etc., the result will vary, but will not be worse than the sin of the angle. I'll draw out better picture with more detail for Vancouver. We're at a fairly high latitude, so overall array orientation is a more sensitive factor than farther south. 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: mailto:jarmo.venalai...@schneider-electric.com jarmo.venalai...@schneider-electric.com | Site: http://www.xantrex.com/ www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Brian Mehalic br...@solarenergy.org mailto:br...@solarenergy.org To: RE-wrenches re-wrenches@lists.re-wrenches.org mailto:re-wrenches@lists.re-wrenches.org , Date: 07/28/2015 09:48 AM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org mailto:re-wrenches-boun...@lists.re-wrenches.org _ The analysis of 50% of south facing production is too simplistic; running some modeling shows that, depending on the latitude, the difference can be much smaller, approaching 25% less for the north facing. I think this layout could become more common especially on low slope commercial roofs, where the north facing module would occupy space that was already unused due to interrow shading. Of course the closer to the equator the less difference between production of the north and south arrays...and you better be careful when stringing them in series so as not to mix N and S facing..plus filling in all those gaps between rows could make servicing the array a bit problematic! Cheers, Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org http://www.solarenergy.org/ On Tue, Jul 28, 2015 at 10:24 AM, billbroo...@sbcglobal.net mailto:billbroo...@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: mailto:re-wrenches-boun...@lists.re-wrenches.org re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of mailto:jarmo.venalai...@schneider-electric.com jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 8:04 AM To: RE-wrenches mailto:re-wrenches@lists.re-wrenches.org re-wrenches@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: tel:%2B604-422-2528 +604-422-2528 | Tech Support: tel:800-670-0707 800-670-0707 | Mobile: tel:%2B604-505-0291 +604-505-0291
Re: [RE-wrenches] Using the North Facing Roof
The intent of the simple example was to show that production is not severely affected by unusual orientations. I will clarify my message. 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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: billbroo...@sbcglobal.net To: 'RE-wrenches' re-wrenches@lists.re-wrenches.org, Date: 07/28/2015 12:20 PM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org Jarmo, Unfortunately, simple is wrong in this case—and detrimental to the PV industry that needs all the roof real estate it can find. Bill. Bill Brooks, PE Principal Brooks Engineering From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 10:43 AM To: RE-wrenches re-wrenches@lists.re-wrenches.org Subject: Re: [RE-wrenches] Using the North Facing Roof Hi: Granted that the description is very simple, but that is the intent. The essence of it is that the loss for small variations in angle of incidence is approximately bounded by, (less than), the sin of the angle between the orientations of two panels/arrays in question. 10 degrees --- minus 17% 20 degrees --- minus 33% 30 degrees --- minus 50% If you go through the detailed math and take into account atmospheric effects, especially when the sun is near the horizons, temperature, location, weather, etc., the result will vary, but will not be worse than the sin of the angle. I'll draw out better picture with more detail for Vancouver. We're at a fairly high latitude, so overall array orientation is a more sensitive factor than farther south. 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.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Brian Mehalic br...@solarenergy.org To: RE-wrenches re-wrenches@lists.re-wrenches.org, Date: 07/28/2015 09:48 AM Subject: Re: [RE-wrenches] Using the North Facing Roof Sent by: RE-wrenches re-wrenches-boun...@lists.re-wrenches.org The analysis of 50% of south facing production is too simplistic; running some modeling shows that, depending on the latitude, the difference can be much smaller, approaching 25% less for the north facing. I think this layout could become more common especially on low slope commercial roofs, where the north facing module would occupy space that was already unused due to interrow shading. Of course the closer to the equator the less difference between production of the north and south arrays...and you better be careful when stringing them in series so as not to mix N and S facing..plus filling in all those gaps between rows could make servicing the array a bit problematic! Cheers, Brian Mehalic NABCEP Certified Solar PV Installation Professional™ R031508-59 PV Curriculum Developer and Instructor Solar Energy International http://www.solarenergy.org On Tue, Jul 28, 2015 at 10:24 AM, billbroo...@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-boun...@lists.re-wrenches.org] On Behalf Of jarmo.venalai...@schneider-electric.com Sent: Tuesday, July 28, 2015 8:04 AM To: RE-wrenches re-wrenches@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
Re: [RE-wrenches] Using the North Facing Roof
Bill and Wrenches, I have been battling this issue for a while. Our sales folks are up against fierce competition and want to design a system that has the best return on investment. So, they will choose a reverse tilt system over a North facing array unless there is a strong deterrent to going with reverse tilt. This deterrent could come in the form of a company policy “no reverse tilts” or by adding significant costs to reverse tilt systems. We’ve tried some of both and there are still cases where reverse tilts prevail – but we do them very seldom and only with careful consideration. Let’s say we have a 5 kW grid tied system (off grid is a whole other ball of wax) and we’re analyzing our options between flush mount North 18 degrees (4:12 pitch) and reverse tilt to South at 5 degrees. The North facing array will produce about 24% less than the South facing reverse tilt system assuming no differences in shade for our Bay Area location or 5126 kWh/yr for North versus 6758 kWh/yr for South. At $0.20/w for electricity this amounts to $326/yr of extra savings for the South facing reverse tilt system. We might charge about an extra $1500 to install the reverse tilt system to account for the engineering cost to check the structure and extra racking material and labor. This means that the reverse tilt system pays off in less than 5 years. The numbers would be more in favor of the reverse tilt if the North facing pitch was steeper. I guess all I’m saying is that the pure numbers still support reverse tilts in some cases. Despite that, my gut is that we should avoid them for the same reasons that Bill lists below. Best, August *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *billbroo...@sbcglobal.net *Sent:* Tuesday, July 28, 2015 11:16 AM *To:* 'RE-wrenches' *Subject:* Re: [RE-wrenches] Using the North Facing Roof 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-boun...@lists.re-wrenches.org re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Starlight Solar Power Systems *Sent:* Tuesday, July 28, 2015 9:41 AM *To:* RE-wrenches re-wrenches@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.parr...@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
Re: [RE-wrenches] Using the North Facing Roof
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.wh...@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.wh...@rgsenergy.com william.wh...@rgsenergy.com * *Confidentiality Note: *This e-mail message may contain confidential or legally privileged information and is intended only for the use of the intended recipient(s). Any unauthorized disclosure, dissemination, distribution, copying or the taking of any action in reliance on the information herein is prohibited. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, or contain viruses. Anyone who communicates with us by e-mail is deemed to have accepted these risks. RGS Energy is not responsible for errors or omissions in this message and denies any responsibility for any damage arising from the use of e-mail. Any opinion and other statement contained in this message and any attachment are solely those of the author and do not necessarily represent those of the company. *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Chris Mason *Sent:* Tuesday, July 28, 2015 1:50 PM *To:* RE-wrenches re-wrenches@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, billbroo...@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-boun...@lists.re-wrenches.org] *On Behalf Of *jarmo.venalai...@schneider-electric.com *Sent:* Tuesday, July 28, 2015 8:04 AM *To:* RE-wrenches re-wrenches@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.venalai...@schneider-electric.com | *Site:* www.Xantrex.com http://www.xantrex.com/ | *Address:* 3700 Gilmore Way, Burnaby, BC V5G4M1 http://www.xantrexrebate.com/ http://www.xantrex.com/ https://www.facebook.com/Xantrex https://twitter.com/Xantrex https://twitter.com/Xantrex *** Please consider the environment before
