[RE-wrenches] Using the North Facing Roof

Tue Jul 28 09:24:59 PDT 2015

Jarmo,

The sun’s geometry is not nearly that simple. To understand the impact of north-facing arrays, you have to perform a simulation. PV:WATTS does this just fine and it is easy to show that a 18-degreed North-facing tilt produces 75% of a perfect 30-degree south-facing array. Far more than your assumption of 50%.

To compare 15-degrees South to 15-degrees North, the numbers are slightly better at 77%. We are going to see a lot of north-facing arrays once people understand that low tilt angles are very forgiving on North slopes. Steep slopes are a totally different story and you have to run the numbers….

Bill.

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jarmo.Venalainen at schneider-electric.com
Sent: Tuesday, July 28, 2015 8:04 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Using the North Facing Roof

I did a slide on the effect of North facing modules.  For even a fairly aggressive rotation North as shown, the effect is "only" a 50% reduction. 

The questions of whether or not to do it, are, 

- is the mounting structure simpler, lower cost 
- security against wind 
- can I put a larger array on the roof  (typically yes, if you make back to back pyramid shaped structures) 
- overall, what is the cost versus benefit 

JARMO
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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 
petertor at pobox.com <mailto:petertor at pobox.com>  

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