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diy solar

More sun hours or optimized direction?

Joes_Going_Solar

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Jul 2, 2022
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I live in LP of Michigan, my house roof faces North/South and my garage roof faces East/West. both have a somewhat shallow pitch 4/12 & 5/12, but both get sun for probably 2+ hours a day over any open space where I would be able to place a ground mount. Would it be better to optimize direction and angle on a fixed ground mount with less sunlight hours or use my home and garage roof with longer sun exposure? Is there a calculator somewhere for this?
 
There's arguments either way depending on who you ask, and I bet someone will be along shortly to link to studies that have been done about it, but it really comes down to personal preference.

Myself, if I had 1200w worth of panels (as an example that napkins easily) I would rather do 3 strings across the southern sky than do a single larger array just due south and that's because while a single large array will probably produce more usable watts at once, the window of opportunity is very narrow and if there's a cloud at noon you're screwed. With a wide angle array if there's clouds in the morning I still get SOME production later in the day rather than NO production all at once.

Other people who don't have to worry about clouds and overcast in desert-y places will probably gain more benefit from one HUGE array all facing south because the sun will always be perfect and clear.

Tl;Dr: It really depends on your environment and location, and if you ask 500 forum members you'll get 768 different answers. :)
 
What are you using the power for?
Seasonal? Snow cover?

Your roofs are pretty shallow. Can you tilt the panels? Latitude +/- 15 deg would be good.
 
PVwatts is the program you want.

 
My neighbor finally cut down a tree and I was able to have east facing panels. They produce more power than all my other panels combined. I get power just when I need it in the morning. Panels are cheap now. This whole idea of throwing everything into a big battery is just an old way of thinking when panels were expensive and batteries were cheap. All my other panels see less than 2 hours of sun and they are still worth having.
 
My own house faces E/W and I opted for a ground mount facing south to increase production. At my location, tilt isn't a huge factor. I lose about 8% from the optimal tilt to where I have them at 10deg, which is not a lot IMO because the alternative on the roof was 20% less when facing E/W. I modeled all these options.

If you have a roof facing South without a lot of shading, that is your best option. If there is morning/evening shading, facing panels in that direction (E/W) will worsen the production.

Also, a roof-mounted racking system with rails is about $60/panel. A 10-deg ballasted system like mine is about $75/panel, and a full-tilt ground mount is between $100-$200 per panel, depending on if you use wood, pipes, Unistrut, or single-post. I haven't seen a ground mount done for less than this without the builder having the materials already on-site and available for free.

You should consider what the ROI is to you. Paying 2X to 3X more for racking will take how long to pay off, compared to putting them on the roof?

Screen Shot 2022-06-15 at 3.29.16 PM.png
 
My own house faces E/W and I opted for a ground mount facing south to increase production. At my location, tilt isn't a huge factor. I lose about 8% from the optimal tilt to where I have them at 10deg, which is not a lot IMO because the alternative on the roof was 20% less when facing E/W. I modeled all these options.

If you have a roof facing South without a lot of shading, that is your best option. If there is morning/evening shading, facing panels in that direction (E/W) will worsen the production.

Also, a roof-mounted racking system with rails is about $60/panel. A 10-deg ballasted system like mine is about $75/panel, and a full-tilt ground mount is between $100-$200 per panel, depending on if you use wood, pipes, Unistrut, or single-post. I haven't seen a ground mount done for less than this without the builder having the materials already on-site and available for free.

You should consider what the ROI is to you. Paying 2X to 3X more for racking will take how long to pay off, compared to putting them on the roof?

View attachment 101013
What are those, lawn chairs with a brick on them?
 
The greatest insolation is mid-morning to mid-afternoon so you want to maximize panel face exposure during these times.

In Michigan you have low sun angles above horizon, especially in winter, so shallow pitch roof is not good. Shallow roof and snow buildup is another consideration.

solar-intensity-vs-incidence to horizon.png

NREL solar data Lansing MI.jpg
 
What are those, lawn chairs with a brick on them?
LOL! No, they are Unirac RM10 racking systems for flat roofs. There is also an RM5 and a Gridlock ballasted system.
Iron Ridge makes a similar system out of plastic, the BX10 but it requires bonding jumpers between rows, this one does not. It is easy to set up alone, no posts, no rails, and no mixing concrete. All it really needed was to roll out some weed barrier and lay down the racks as level as possible. They can take quite a bit of offset between racks.
 

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I plan to use the solar to take most of my home off grid. I'm going to keep my large loads (AC, dryer) on the grid. My WH and oven are propane. My house roof faces 185 deg south this may be my best option. The area where I could place a ground mount is approx 220' away from my garage (where I plan to mount the inverter and battery). And my detached garage is only 25' from the house. There will be snow cover in the winter but the house is a single story so I should be able to remove it fairly easily. On another note my entry Door knob is dark bronze color and in the summer it will nearly burn my hand when the sun is shining in the afternoon.
 
I have 36 used panels, divided into 4 strings of 9 panels. I have one string pointed East, and one pointed West, combined. Then I have two pointed South, combined.

Here are the East/West and the South arrays inputs overlayed:
56A1C6DC-2664-45A5-96D0-F5398C5E38BE.jpeg316E3D0D-E184-4D69-A17C-B84607A9A464.png
(Putting in xeriscape landscaping, front yard done now.)
 
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