Solar Wiring Size

[machyoung]

Have read through hundreds of posts however can not find the definitive answer that I am looking for. Installing solar on my 18 Ace 29.3 which is "pre-wired" for solar. We all know that means 10g wire from roof to inside. I am installing 2 - 170 watt panels to a MPPT charge controller and so on. Question; How inadequate is the 10g wire for 340 watts and what we would be the best wire size? I ask because the wire routing is a challenge and I am trying to avoid it until my next upgrade? I will eventually upgrade the wire and possibly install a third panel. Thanks in advance for any suggestions. Robert

[taylorbob1]

I used 10 gauge stranded wire for my 200 watts of solar (two 100 watt panels)
If I add another 200 watts (four 100 watt panels total), I will NOT change the wire size to 8 gauge

That is, I feel comfortable with 10 gauge for 400 watts of solar


P.S. see my solar install on this thread

Drill-less Solar Mounts

[Chance]

Originally Posted by machyoung

....cut.... Thanks in advance for any suggestions. Robert

The issue with wire size to worry about is Amps, not Watts. Therefore, it depends on whether you will wire the two panels in series or parallel. If you have specs on panels, maybe post a link.

[Crossleyt]

Originally Posted by machyoung

Have read through hundreds of posts however can not find the definitive answer that I am looking for. Installing solar on my 18 Ace 29.3 which is "pre-wired" for solar. We all know that means 10g wire from roof to inside. I am installing 2 - 170 watt panels to a MPPT charge controller and so on. Question; How inadequate is the 10g wire for 340 watts and what we would be the best wire size? I ask because the wire routing is a challenge and I am trying to avoid it until my next upgrade? I will eventually upgrade the wire and possibly install a third panel. Thanks in advance for any suggestions. Robert

348 Watts at 12 VDC is 29 Amps of current. 10 AWG wire is rated for 30 minimum. Some insulation types are rated higher.

[Chance]

Originally Posted by Crossleyt

348 Watts at 12 VDC is 29 Amps of current. 10 AWG wire is rated for 30 minimum. Some insulation types are rated higher.

With panels flat on roof like in most installations, and voltage from panels to controller significantly higher than 12 VDC, it would not surprise me if current is closer to +/- 20 Amps, even when wired in parallel.

Panel performance curves would be valuable.

[machyoung]

https://amsolar.com/s/AM-SOLAR-ZS170.pdf

I attempted a link to the panels above. I appreciate all input.

[Chance]

Originally Posted by machyoung

https://amsolar.com/s/AM-SOLAR-ZS170.pdf

I attempted a link to the panels above. I appreciate all input.

Thanks.

You can see each panel should not even reach 10 Amps, so if you connect them in parallel, your current should be under 19 Amps.

If you connect them in series, your current should be under 10 Amps.

From a wiring perspective you should be able to expand system in the future. Note maximum power is at 18 VDC, with open circuit about 24 VDC. If you decide to wire in series, the max voltage should still be relatively safe.

In future you could expand to 4 panels in combination of series and parallel, which would limit your current to under 20 Amps from roof to controller, assuming MPPT controller has adequate capacity. Just saying that if it were me, I’d size other components and wiring for future expansion just in case you decide to add more later.

[machyoung]

https://amsolar.com/rv-controller-sy...0s-sig-mpp-40a

This is the system I have w/ 2 of the panels I attached in the previous post. I will not be running the 4/2 wire from the roof to the charge controller.

[Ejohn2317]

www.mobile-solarpower.com

Mobile Solar power made easy by William Prowese
His book sold on amazon is a step by step guide to rv solar install.

[petefoss]

Originally Posted by Ejohn2317

www.mobile-solarpower.com

Mobile Solar power made easy by William Prowese
His book sold on amazon is a step by step guide to rv solar install.

Thanks for the link. Interesting stuff

[DenverTransplant]

The size of solar wiring depends upon the losses caused by wire resistance. Typically you don't want to lose more than 5%, although I would rather see 2% if it doesn't make a big difference in wire size. Arizona Wind and Sun has a handy table of wire losses and has a brief explanation of what is going on.

https://www.solar-electric.com/learn...s-tables.html/

With solar you have two choices of charger technology. PWM (Pulse Width Modulation) is for lower power systems and can only handle parallel panels (Nominally 18 volts). MPPT (Maximum Power Point Tracking) can handle higher power and supports panels wired in series (36, 44, 72 volts). MPPT can be more efficient. Running panels in series reduces wire sizes as you have a long more voltage, which means lower current, and lower losses.

Right now I have 200 watts on the roof (2 100 watt panels) wired in parallel with a PWM controller. I can go to 400 watts without having to change out the controller. As I have a parallel installation, the voltage available is 18 volts - I ended up running 10 ga wire from each panel to the refrigerator vent where I connect to 6 gauge wire running down the vent and across the belly compartment to the solar charger. I forget the calculated losses, but they are on the 2% end, assuming that I expand to 400 watts. Each of the 10 gauge sections carries between 5 and 6 amps which results in acceptable losses for the short runs. But the 6 gauge section can carry as much as 33 amps. Running 10 gauge all the way would result in unacceptable losses.

If I'd set up a series installation, 4 panels could generate 72 volts, which means about 5.6 amp in a single circuit. This allows smaller wire. However, in a series set up, shade on one of the panels can kill the whole string so I chose to stay away from series. In some larger installations, people will have 2 or 3 parallel circuits with multiple panels in series in each circuit.

[petefoss]

Originally Posted by DenverTransplant

However, in a series set up, shade on one of the panels can kill the whole string so I chose to stay away from series. In some larger installations, people will have 2 or 3 parallel circuits with multiple panels in series in each circuit.

Interesting comment. First disadvantage I have heard of a series setup besides the cost of the charger.

[Chance]

Originally Posted by DenverTransplant

.....cut....

If I'd set up a series installation, 4 panels could generate 72 volts, which means about 5.6 amp in a single circuit. This allows smaller wire. However, in a series set up, shade on one of the panels can kill the whole string so I chose to stay away from series. In some larger installations, people will have 2 or 3 parallel circuits with multiple panels in series in each circuit.

From a safety standpoint, I’d base voltage at maximum the panel can generate and not what it typically operates at. Manufacturers supply this data. With open circuit, voltage can easily go into mid 20s or higher depending on panel model, so 4 in series can get high enough to shock/kill.

About 60 Volts is maximum considered somewhat safe in case of shock, so many installations with 4 (typical) panels go with 2 X 2 (series and parallel) or all parallel. It’s important to look at maximum panel voltage because some are designed for even higher operating conditions (like those optimized for 48VDC systems).

[Ejohn2317]

https://www.youtube.com/channel/UCoj...q8kmJme-5dnN0Q
Check out William Prowse you tube channel. This guy explains everything you need to know about solar, batteries and inverters.

[AAL787]

Originally Posted by Ejohn2317

https://www.youtube.com/channel/UCoj...q8kmJme-5dnN0Q
Check out William Prowse you tube channel. This guy explains everything you need to know about solar, batteries and inverters.

I agree. Will is a really cool guy. His enthusiasm about “geeking out” is contagious!

[Brabo]

This is a new question from a solar newbie. How much solar do I need. I’m probably not going to do much boondocking but would like to keep my batteries charged and use the power of the sun here in Florida as much as I can. Places like Harbor Freight sell a 4 panel 100w setup, is that enough? My Chateau is prewired and has a controller. What advise can anyone give on the best direction to go, not necessarily the cheapest or most expensive but most effective.
Thanks. David

[taylorbob1]

100 watts may be enough, but no need to have four 25 watt cheap Harbor Freight panels when you can fasten one 100 watt panel for abt $100.

If you have two house batteries, I would recommend two 100 watt panels.
That is about $200 and you have an inexpensive, but efficient way to charge batteries (and even boon-dock)

You can also mount flexible panels instead of solid panels for a small additional cost, but much easier to mount and quick to install.

Search the Forum for lots of insight on this topic.

Please share your final mod with photos and analysis.