Run PV wiring on Power Poles

mjp24coho · December 2016

Question for the group here. I'm looking at doing a large new solar field on top of the hill behind my cabin (much better solar exposure). It's ~150' from the top of the hill down to my cabin. The only problem is that it is very steep (too steep for trenching equipment), and the hill is full of granite, so trenching is not an option. I'm wondering if running the 2-3 PV strings through the air would work - via (2) power poles. The hill is full of Juniper trees, but none over 30-40', so running the wire over 50' from the tops of the two poles should be free from any obstructions. Any drawbacks to this? Does Code allow for something like this?

BB. · December 2016

Do you have lightning in the area?

Otherwise, need voltage/current of array (panel configuration), charge controller, and battery bank voltage (to figure out wire gauge).

Figure out copper vs aluminum vs MPPT low voltage (100 Vmp max) or high voltage (~400 volts max Vmp) combinations and trade-offs.

-Bill

Photowhit · December 2016

mjp24coho said:

Does Code allow for something like this?

Do you have codes to worry about where you are?

mjp24coho · December 2016

I don't really have code to worry about (remote off-grid). However, I'm looking at this for a possible expansion where I would be building a large cabin/home on my property. If I do it, I'll likely want to make sure I'm code-compliant so that I can get all the necessary property insurance. The array would be quite large - (60) 265W panels (hence the reason for placing it on the hilltop, where the solar production is greatest and it's out of sight. I would likely use (5) Midnite Classics (each Classic would have 3 strings with 4 30V panels per string) with a 48V battery bank. I would use 4 AWG wiring from the combiner to the charge controller (assume 200' one-way). Lightning is a moderate concern in the area.

mike95490 · December 2016

If lightning is a likely, you want to robustly ground your array frame, so it takes the brunt of the hit. You will loose some panels (likely the end panels of the top row, and bottom row - where the pointy corners that attract lightning are).
Think of schemes that will minimize lighting wanting to follow your DC wires down the hill and into your power room.

mjp24coho · December 2016

Good suggestions on the lightning protection. Regarding running the wiring above ground on power poles (panels to charge controller) - does anyone know if this is code compliant?

Photowhit · December 2016

I don't know, I asked about codes since I might consider trimming out a few of the Juniper trees, and ring them (so they die) they have an extensive root system and I would think as good as some poles and the hassle of drilling in rocky area. Just some creative thinking...

mcgivor · December 2016

Do a proper job, use neutral support triplex cable with insulators, ground the support at every pole, put a lightning rod on each pole to ground and make the installation look professional, when the time comes to build it may be accepted as is or with slight modification. Usually it's better to ask for forgiveness than permission, my experience with electrical inspectors.

Estragon · December 2016

The generator shed at my cabin was about 400' away on the far side of a steep hill when I bought the place, maybe to keep the noise down. Power lines were just attached to live trees with ceramic insulators and were like that for 30 years.

Would it make any sense to fuse at the array in case a squirrel chews wire or a tree falls on it and shorts?

mike95490 · December 2016

Estragon said:

The generator shed at my cabin was about 400' away on the far side of a steep hill when I bought the place, maybe to keep the noise down. Power lines were just attached to live trees with ceramic insulators and were like that for 30 years.

Would it make any sense to fuse at the array in case a squirrel chews wire or a tree falls on it and shorts?

Likely not. Just fuse/Ckt breaker back at the controller and use large enough wire. If you try to fuse at the array, you may get false trips from solar peak power, and consume a lot of fuses.
A breaker at the controller PV input is handy for testing, and protects the PV wire from a faulty controller

HarryN · February 2017

It might be worth considering to do the entire (PV panels + 48 volt battery system + inverters) in the same location, and wire over the 120 or 240 VAC to the cabin area. The wire size needed to transmit the same power in 240 VAC will be much smaller than doing it with 48 VDC. Also if you do it with AC, then it is also possible to compensate for wire loss a bit easier with a transformer.

BB. · February 2017

Schneider and MorningStar have some ~600 VDC input max MPPT charge controllers (others too?). You can run the array at Vmp~400 volts in most climates with a 600 VDC input charge controller--Even better than the 120/240 VAC split phase power--Plus you can put all of the hardware and batteries next to the home instead of a long hike out.

-Bill

mvas · February 2017

Photowhit said:

I don't know, I asked about codes since I might consider trimming out a few of the Juniper trees, and ring them (so they die) they have an extensive root system and I would think as good as some poles and the hassle of drilling in rocky area. Just some creative thinking...

The NEC prohibits the use of trees as support between spans of permanent overhead cables.
Trees are allowed to support temporary and/or holiday lighting.

mvas · February 2017

mjp24coho said:

Question for the group here. I'm looking at doing a large new solar field on top of the hill behind my cabin (much better solar exposure). It's ~150' from the top of the hill down to my cabin. The only problem is that it is very steep (too steep for trenching equipment), and the hill is full of granite, so trenching is not an option. I'm wondering if running the 2-3 PV strings through the air would work - via (2) power poles. The hill is full of Juniper trees, but none over 30-40', so running the wire over 50' from the tops of the two poles should be free from any obstructions. Any drawbacks to this? Does Code allow for something like this?

See Article 225 of the NEC for permanent overhead cable span regulations.
Most of the rules that apply to an Overhead Service Entrance would apply to here.

Summary:
http://ecmweb.com/code-basics/article-225-outside-branch-circuits

Overhead cable management systems ...
https://www.cabproducts.com/wp-content/uploads/2014/12/CAB_Cable_Management_White_Paper_9-18-2014_2.pdf

Run PV wiring on Power Poles

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