Everything Solar Forum

This array faces south but is supported by Unirac high-profile tilt legs on the north side of my hip roof.  I use them to seasonally adjust tilt angle.  I don't think they are really the right solution for you but it may give you some ideas.

This array faces south but is supported by Unirac high-profile tilt legs on the north side of my hip roof.  I use them to seasonally adjust tilt angle.  I don't think they are really the right solution for you but it may give you some ideas.

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Mike Curran
Retired EE
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@Mike Curran:

Just curious, what is the ASCE wind speed in your location, and was the racking with those tilt legs at that high angle assessed structurally to withstand it?

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Ken Nadsady
AviSun Renewable Energy
Hudson OH
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Original Message:
Sent: 09-03-2024 01:40 PM
From: Mike Curran
Subject: Slar panel mounting

This array faces south but is supported by Unirac high-profile tilt legs on the north side of my hip roof.  I use them to seasonally adjust tilt angle.  I don't think they are really the right solution for you but it may give you some ideas.

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Mike Curran
Retired EE

Don't  know, and no structural assessment done.  House is pretty well surrounded by trees, and that array has been up since 2007.  Last August (2023) we had a large live cherry tree fall on our barn during a windstorm.  That occurred with the house array panels/struts in their summer position, fairly flat (~25° IIRC).

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Mike Curran
Retired EE
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Original Message:
Sent: 09-04-2024 09:20 AM
From: Ken Nadsady
Subject: Slar panel mounting

@Mike Curran:

Just curious, what is the ASCE wind speed in your location, and was the racking with those tilt legs at that high angle assessed structurally to withstand it?

------------------------------
Ken Nadsady
AviSun Renewable Energy
Hudson OH


Original Message:
Sent: 09-03-2024 01:40 PM
From: Mike Curran
Subject: Slar panel mounting

This array faces south but is supported by Unirac high-profile tilt legs on the north side of my hip roof.  I use them to seasonally adjust tilt angle.  I don't think they are really the right solution for you but it may give you some ideas.

------------------------------
Mike Curran
Retired EE

Without knowing were you are (Unless I missed it), a comment would be futile for the most part.

North side panel installation was not even a "thing", until they got so cheap it began to make sense, depending on the exact circumstances of the site. Low roof angles are pretty much required and generally you should be happy you get much of anything at all, given a true north install.

Latitudes under 20deg can fair not too badly. North of that gets progressively worse. North of 40, Winter will be in the toilet.

I would be happy and leave it alone, with a quality install. If its not broken, don't fix it.

Hello Michael

I also was shocked when about 8 years ago I saw the first residential system in my neigborhood with both south and north facing modules. (I Live in Delaware). Then I thought about it. (I teach a class on solar technology applications). The cost breakdown for a residential system nowadays has the price of modules at less than 30% of the total installed price. So adding modules on the north makes sense since they incrementally add a small amount to  the rest of the fixed costs.  Adding 10% more cost but getting 60% more energy (see below) makes sense! As others have said, this new strategy was only possible due to the dramatic decrease in module pricing. And remember that rear facing modules see all the same diffuse hazy light that front modules see whcih is about 20-30% of the total over a year.

To verify this, I went to the NREL PVWatts calculator https://pvwatts.nrel.gov/pvwatts.php. I assumed a 1 kW ssytem facing S (180 deg azimuth) or N (0 deg azimuth). I assumed a slope of 30 degrees and calculated the output for a N and S facing systems in Dallas or Chicago. Results are:

Dallas: N- 1516 kWh, S-905 kWh or 40% less energy for the N facing array.

Chicago: N-1329 kWh, S-729 kWh or 45% less energy for N facing. This is expected since the farther N you are the less light on the rear. 

If your slope is less than 30 degrees it gets much better especially the farther N you are. So that is why it is cost effective to put modules on the N.

 I will say I am a little surprised that you ahve THREE times as many modules facing N than S. That is very unusual in my experience and in my opinion not a good deal for you given that 66% of your modules are getting much less energy than the remaining 33%. Which skews the payback against you. 

Steve 

Thanks everyone for your replies and comments!  They were all quite helpful.  With this old farm house, the majority of the panels being on the north side of the house ended up being inevitable, hence the 39 panels for a 14KW system.  I like the "If it ain't broke, don't fix it" quote - as that seems applicable in my situation here in central KY.  My original goal was to ensure as close to 100% electrical cost being covered by the panels, and that has been the case so far.  I had the panels installed in July, and so far they are producing twice the power we use, so I can't complain too much.  I think I'll forego modifications to the angle of the panels on the north side, since they are sitting on the roof of a 150 year old house that was definitely not designed with solar in mind.  If over time I find more production is needed, I always have the option to put panels on the adjacent garage once I have a new roof put on it.  I did end up with the majority of my panels on the north facing roof, due to the area of roof I had available to work with, so with all things considered, I suppose it was cheaper to add more panels there for incremental increases in production over none at all.  Again,  thanks everyone.

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MICHAEL MILLER
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