Author Topic: off-grid wiring best practices?  (Read 3986 times)

Offline Smurf Hunter

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off-grid wiring best practices?
« on: June 30, 2016, 12:29:02 PM »
I know a little about voltage drop on DC wires.  I've read, and it makes sense to me, that I should not have long length of wires between battery and controller.

If I must have some distance between PV panel and battery due to the installation location, can I get away with longer wires between controller and PV panel?  They sell 100 ft. cables with MC4 connectors, so that validates my thinking a bit.

Seems like I could buy the MC4 ends (https://www.amazon.com/RENOGY®-Female-Connectors-Double-Waterproof/dp/B00H1M8ASE), and a long length of 12awg wire and run that to wherever my operating location is. 

I already have some portable 12v battery capability and initially wanted solar to supplement that.  Right now I only have a 100watt renogy mono panel.





Also, for home roof mounting, what are the best practices for running cables into attics, etc?  Last thing I need is a leaky roof and expensive divorce.

Offline Cedar

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Re: off-grid wiring best practices?
« Reply #1 on: June 30, 2016, 12:51:00 PM »
Also, for home roof mounting, what are the best practices for running cables into attics, etc?  Last thing I need is a leaky roof and expensive divorce.

Asking her opinion?  ;)

Cedar

Offline xxdabroxx

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Re: off-grid wiring best practices?
« Reply #2 on: June 30, 2016, 12:58:39 PM »
I know a little about voltage drop on DC wires.  I've read, and it makes sense to me, that I should not have long length of wires between battery and controller.

If I must have some distance between PV panel and battery due to the installation location, can I get away with longer wires between controller and PV panel?  They sell 100 ft. cables with MC4 connectors, so that validates my thinking a bit.

Seems like I could buy the MC4 ends (https://www.amazon.com/RENOGY®-Female-Connectors-Double-Waterproof/dp/B00H1M8ASE), and a long length of 12awg wire and run that to wherever my operating location is. 

I already have some portable 12v battery capability and initially wanted solar to supplement that.  Right now I only have a 100watt renogy mono panel.

Also, for home roof mounting, what are the best practices for running cables into attics, etc?  Last thing I need is a leaky roof and expensive divorce.

Leaving the longer leads between the panel and controller makes sense to me.  The controller is receiving the lower voltage from the panel, and not reading that the battery has less voltage that it really does.  (I'm no expert, but I know a little about wiring FWIW)

Best and easiest option for getting into the roof would probably be to run wire down roof and then back up under the eave and enter there.  That should remove the chance of water intrusion.  As for mounting it to the roof, I'd get in touch with a roofer.  I draw houses for a living but I'm not super familiar with modifying an existing roofing system.  Starting from scratch I'd think you would make roof jacks with flashing that would go over the lower shingles and under the upper shingles to prevent water intrusion.  I'm not sure how to go about retrofitting though.  I hate poking holes in roofing, I have to open one up on my roof soon to run a dryer duct through and I'm not looking forward to it.   

Offline jerseyboy

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Re: off-grid wiring best practices?
« Reply #3 on: June 30, 2016, 01:51:41 PM »
Great purchase!!!

As your system grows you may want to consider an MPPT charge controller that can handle 100V+ inputs.  These take 5 panels in series but still produce electricity in lower sun conditions. As understand it, this works because the voltages add.

Under full sun, let's say one panel makes 17 volts. PWM charger will charge your battery as long as your panel voltage remains high enough. That means if the clouds cover the sun and your voltage drops to 11 volts, you will not be charging.

An MPPT charger that takes up to 100 volts can take 5 full sun panels at 85 volts but let's say you only have two connected in series. In full sun you get 34 volts which can charge your batteries. When the clouds cover the sun the voltage can drop to 22 (2x11) and still be able to charge the batteries.

As you build your system (4x100 watt panels on that 30amp 12V charge controller) preserve a path to go back and wire them in series over the parallel way using the PWM one you are using now.

Jerseyboy

Offline Carl

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Re: off-grid wiring best practices?
« Reply #4 on: June 30, 2016, 04:32:33 PM »
Your assumptions are correct and 12 ga wire is good enough as it is way too costly to chase that 2% loss
(much like SWR,not worth worry) and keep wires short to the battery ,from the controller.
I attached my panel to the facure board and built small legs for best solar angle so as to have a 'wind stable' attachment
with no holes in the roof. Pass wires through vent on roof overhang and pass down through closet ceiling to battery area....
expect about 4 to 5 amps charging with full sun times of 5 to 6 hours.

Offline Smurf Hunter

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Re: off-grid wiring best practices?
« Reply #5 on: June 30, 2016, 04:57:23 PM »
Your assumptions are correct and 12 ga wire is good enough as it is way too costly to chase that 2% loss
(much like SWR,not worth worry) and keep wires short to the battery ,from the controller.
I attached my panel to the facure board and built small legs for best solar angle so as to have a 'wind stable' attachment
with no holes in the roof. Pass wires through vent on roof overhang and pass down through closet ceiling to battery area....
expect about 4 to 5 amps charging with full sun times of 5 to 6 hours.

I like this.  I'm crafting a plan.  I know from backyard gardening, that the south side of my property gets the most sunlight overall.
Problem is, my current shack location is in the NE corner upstairs.  This works well for my antenna feedline, which I run from a bedroom closet up into the attic.  It would be convenient if I could leverage the same path for the 12awg PV panel wire.  We're talking about 50 feet or so of wire if I run everything like this.



I could perhaps move the panel towards the front of the house, but then I have to worry more about it looking pretty.  I also don't have the attic fully above the shack location, so running wire is much more difficult.

Option 2 saves a lot of cabling, but I'd have to sneak the wire under the roof vent on the front of the house.  Higher chance of angering the XYL, but it still warrants consideration.


Offline Carl

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Re: off-grid wiring best practices?
« Reply #6 on: June 30, 2016, 05:14:36 PM »
You can build a PVC rack to hold the panel and use sand bags to weigh it down,plus the wedge of the panel will do OK in wind and the high side of the panel(that would catch the most wind) is protected by the roofline and not so vulnerable...appease the wife and use a bit more wire...it is just not worth the misery to go against the COO.

Just a passing thought.

Your house is tall enough that I think the panel might not be so visible as you may think...few people look UP.

Offline Alan Georges

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Re: off-grid wiring best practices?
« Reply #7 on: July 06, 2016, 05:34:04 PM »
Coming in late to the party, here's an article Jeff Yago published about a year ago:
http://www.backwoodshome.com/solar-system-codes/

It reads like a bunch of dire warnings, but since I'm doing something similar to what you have planned Smurf and haven't had any trouble in 3 years of coastal lightning storms, I suspect you'll be OK too.  Anyway, it's some good background/bathroom reading.  50' with 12ga should be long-ish but fine with the amps your panels will put out.  All looks good, from the pics you've posted.