[RE-wrenches] Using the North Facing Roof
Will White
William.White at rgsenergy.com
Tue Jul 28 11:23:41 PDT 2015
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
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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<mailto: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<mailto:re-wrenches-bounces at lists.re-wrenches.org>] On Behalf Of Jarmo.Venalainen at schneider-electric.com<mailto:Jarmo.Venalainen at schneider-electric.com>
Sent: Tuesday, July 28, 2015 8:04 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org<mailto: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
[cid:image001.gif at 01D0C941.007047C0]
JARMO
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From:
"Peter Parrish" <peter.parrish at calsolareng.com<mailto:peter.parrish at calsolareng.com>>
To:
"'RE-wrenches'" <re-wrenches at lists.re-wrenches.org<mailto: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<mailto: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<tel:%28323%29%20839-6108>
petertor at pobox.com<mailto:petertor at pobox.com>
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Chris Mason
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