Solar Panel mounting question.

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dsciacca

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Nevada City,CA USA
I have an as-built plan to mount 12 240v panels in a stand constructed in pine trees. the stand is approx 20 ft above the ground and is totally built in using 7or 8 live trees to support it. I know that section 225.26 prohibits the use of trees to support overhead conductor spans. These conductors are DC run down the tree, below grade,and 200 ft to the inverter. The entire run is in conduit. I have pictures of this existing work. Any thoughts?
 
dsciacca said:
I have an as-built plan to mount 12 240v panels in a stand constructed in pine trees. the stand is approx 20 ft above the ground and is totally built in using 7or 8 live trees to support it. I know that section 225.26 prohibits the use of trees to support overhead conductor spans. These conductors are DC run down the tree, below grade,and 200 ft to the inverter. The entire run is in conduit. I have pictures of this existing work. Any thoughts?
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Never mind the code, how does this work from an engineering perspective? I assume the trees are stil live and growing, yes? They are growing up and out; how long before the conduit starts to lift out of the ground, or pull away from the stand? Or break apart in the middle? What about the differential growth of the trees causing the stand to tilt? I'm sure others can add to the litany of potential "live support" issues. Sounds like a project a 9-year old dreamed up and it didn't get reviewed by an adult.
 
gadfly56 said:
Never mind the code, how does this work from an engineering perspective? I assume the trees are stil live and growing, yes? They are growing up and out; how long before the conduit starts to lift out of the ground, or pull away from the stand? Or break apart in the middle? What about the differential growth of the trees causing the stand to tilt? I'm sure others can add to the litany of potential "live support" issues. Sounds like a project a 9-year old dreamed up and it didn't get reviewed by an adult.
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I agree that the project sounds ill-conceived, but FWIW, trees grow from the top, not from the bottom. If you nail something to a live tree 6' off the ground and come back 100 years later, it will still be 6' off the ground.
 
ggunn said:
I agree that the project sounds ill-conceived, but FWIW, trees grow from the top, not from the bottom. If you nail something to a live tree 6' off the ground and come back 100 years later, it will still be 6' off the ground.
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Some species, maybe. My dad put eyehooks in a couple of oaks 40 years ago for a hammock. They are now about 12' off the ground. When the builder did my parents' subdivision he planted one or two trees in just about every front yard. A seven-year old couldn't clear the bottom branches. Now my FIL, who is 6'7", wouldn't have a problem. I suggest that at 20' above the ground there is plenty of "up" left in the trunk.
 
gadfly56 said:
Some species, maybe. My dad put eyehooks in a couple of oaks 40 years ago for a hammock. They are now about 12' off the ground. When the builder did my parents' subdivision he planted one or two trees in just about every front yard. A seven-year old couldn't clear the bottom branches. Now my FIL, who is 6'7", wouldn't have a problem. I suggest that at 20' above the ground there is plenty of "up" left in the trunk.
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http://dendro.cnre.vt.edu/forsite/howdoes.htm
 
Shout out to Nevada City! (I lived there from 1995 to 2000.)

As others have suggested, this sounds ill-conceived. It's had to imagine a scenario where it makes sense to make structural use of the trees, just from a solar access perspective.

While it is possible to use trees structurally, it's a little tricky to do it right. I once stayed at a tree house resort in Southern Oregon that had developed some best practices:

http://www.treehouses.com/treehouse/treesort/institut.html
 
I agree 100% but I have a local engineering firm that has stamped this and provided calculation. The calcs appear to be based on dead or cut trees, you have to admit that the size of the material will only get bigger.
 
Exactly. If the trees are big enough to support the structure, how could they not shade the array? (Assuming the trees have not been topped, in which case they are basically standing dead trees.)

Even if none of the trees are located to the south of the array, it stands to reason that they will shade it in the morning and evening. That shading is likely significant when factored over the course of a year. It will also get worse over time.

Did the consulting engineer provide a shade analysis?

They should really evaluate the seasonal shading at each corner of the array, ideally with a Solmetric Suneye or similar, then plug the data into a simulator and quantify the shade impacts.

http://solarprofessional.com/articles/design-installation/solar-site-evaluation?v=disable_pagination
 
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If shading is likely to be an issue, it can be minimized by use of either balancers or microinverters. The options available will depend on whether this is a an off-grid, grid-tied, or hybrid system.

As for the wiring, a simple conduit system without flexible elements will be broken by horizontal growth, although more slowly than by vertical growth.
 
GoldDigger said:
If shading is likely to be an issue, it can be minimized by use of either balancers or microinverters. The options available will depend on whether this is a an off-grid, grid-tied, or hybrid system.
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Of course such devices can pull shaded modules out of the system, but if the array is under a tree canopy, then they really can't help the overall picture very much.
 
ggunn said:
Of course such devices can pull shaded modules out of the system, but if the array is under a tree canopy, then they really can't help the overall picture very much.
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Two words: Amorphous Silicon.

Mono and poly-silicon are worse with shading than amorphous. However, this is still a highly questionable installation.
 
This is a terrible idea! you want to install something, in a living growing and dying group of trees, that will be producing leathal voltage for the nest 1/2 century plus. What about this sounds like a good idea?
 
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