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Old 08-28-2019, 04:10 PM   #1
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Question Series vs. Parallel Solar Panel Wiring

I am planning an upgrade to 4 x 200 W solar panels on my 2018 Navion with a Victron MPPT charge controller. I am planning to use series configuration in order to use the existing #8 wiring with little loss, and relocating the charge controller to be near the batteries and easily add thicker wire there for up to 40 amps. All other wiring does not need to be upgraded.

I have seen some semi-anecdotal stories that - in most RV installations, it is better to wire panels in parallel due to the likelihood of parking under trees, partial shading, etc. as power degradation due to shadows is worse when in series. Keeping parallel wiring implies upgrading all the wires and connections when substantially increasing power to reduce higher current-induced voltage losses (V = I/R). Whereas with higher voltage, and lower current resulting from series wiring can usually use the pre-existing gauge wires with no detriment.

This makes little sense to me. Solar cells are just a bunch of chemical batteries (cells) that are triggered by photons. Internally these cells are wired in a series w/parallel configuration.

If you take four flashlight batteries, where one is weaker, the total power (I x V) produced will always be the same whether they were all wired in series vs. parallel configuration. MPPT controllers will take whatever available input power and generate the best output current and voltage configuration for the current battery state. Why would solar wiring be affected more that regular battery?

In my (way too many) years of poking around as an engineer, I have found many Old Wives Tales, especially when electricity is involved. Can anybody direct me to some official study or documentation? Or have you done a test?
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Old 08-28-2019, 05:24 PM   #2
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I was going to answer differently up to your last paragraph. Now, I will say, get 2 panels, wire them in series and then in parallel, and do some full sun and shading tests. You could do it with just about any size panels, as long as they are identical.


One other thing that makes sense to me, with my experience. The OWTs (Old Wives' Tales) are likely different, depending on the controller type. Parallel for PWM controllers, and series for MPPT controllers (or, maybe in your scenario, series/parallel for MPPT, depending on the voltage and current ratings of the controller).
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Old 08-28-2019, 08:12 PM   #3
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Have tried it both ways, with most new panels having bypass diodes to shunt the current around shaded cells, don't notice much difference in power production. Now running 120 volts on one series string and 60 volts on another series string. Nice to be able to use lighter gauge wire. Mppt controllers of course. Believe most Pwm controllers are only good for panels less than 24 volts which eliminates bigger panels.
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Old 08-29-2019, 12:37 PM   #4
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We're running 12x180w panels.




We've broken them down into two strings of 6 panels, each in series, into individual Victron MPPTs. 1 string for each side of the roof.

We run ~140vdc @10a into each Victron 150/100 MPPT, and it's been working great.


With the bypass diodes built into the panels, if we have shading due to Satellite dish, AC, or whatever else, it simply drops the volts for that panel and continues to operate normally.

This allows us to use 10awg from the panels to the MPPT.

We can charge our batteries at almost 100a @14vdc per MPPT.

Sometimes we even exceed our rated wattage as shown here where we are making almost 25% more.




Panels in series works great and I wouldn't worry about 'shading'.

You don't spend good $ on building a solar system to simply park in the shade.
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Old 08-29-2019, 01:04 PM   #5
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Natebert - now I have "square footage" envy! Drone picture? My little 25 ft Navion simply does not have your roof acreage, but perhaps when Wonder Wife and I decide to go "full time" ...

I really appreciate the charts provided. I assume those power dips equate to clouds passing over?

SLOweather has a good idea - simply run the experiment myself. My panels are arriving next week. I expect it will take some time to install as I need to build an elevated frame to install for one set over the existing Zamp feed-thru connection box now on the roof. I have watched some Dicor removal YouTube videos, and might just move the box too.

I will temp wire up the new MPPT controller where the existing Zamp PWM is, and experiment with series vs. parallel configurations by moving a few panel connections around.

Sometimes parking in the shade is preferable, and sometime unavoidable, but I see your point.
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Old 08-29-2019, 03:11 PM   #6
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here's a great video that shows you the difference.
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Old 08-30-2019, 10:16 AM   #7
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Quote:
Originally Posted by robburns76 View Post
here's a great video that shows you the difference.
That was very educational! They did not mention if their controller was MPPT. But it appears so by comparing images on the Outback website.

I wonder if these results would be duplicated in a more controlled environment, like within my fluorescent lit garage.
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Old 08-30-2019, 10:34 AM   #8
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Quote:
Originally Posted by GyroGypsy View Post
I need to build an elevated frame to install for one set over the existing Zamp feed-thru connection box now on the roof. I have watched some Dicor removal YouTube videos, and might just move the box too.
IF I were you... I'd remove the Zamp 3-port box entirely and create a new connection box with bus bars. That way you can ditch the silly little Zamp SAE connectors and connect your panels directly to bus bars.

OR change everything to MC4 connectors and wire up series or parallel MC4 wire looms.

I'm using the Zamp 3-port and I check my wires every time I'm on the roof. Honestly, it feels like the SAE connectors are barely holding on. Though I admit I've never found one that has dislodged. MC4 connectors seem much more robust and secure.

There are tons of YouTube videos showing large RV solar panel systems wired into waterproof boxes with bus bars inside if you need to see how this is an improvement.
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Old 08-30-2019, 10:51 AM   #9
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Yes, interesting video.

I have 1500w - in three strings of 500w each to one controller. Using three pair of #10 wire to a combiner box near the batteries. I like being able to drop breakers in the combiner box and compare string output. Gives me an idea if panels are working ok.
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Old 08-30-2019, 11:09 AM   #10
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Quote:
Originally Posted by GyroGypsy View Post
That was very educational! They did not mention if their controller was MPPT. But it appears so by comparing images on the Outback website.

I wonder if these results would be duplicated in a more controlled environment, like within my fluorescent lit garage.
I saw that video way back when but have found that for my setup shading effects are not that much different if I have the panels wired series vs parallel. Perhaps the panels they used didn't have bypass diodes which would be surprising as almost all do. Also the OP is talking about a portable setup where shading really isn't a concern.
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Old 09-01-2019, 09:21 AM   #11
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Quote:
Originally Posted by Natebert View Post
We're running 12x180w panels.




We've broken them down into two strings of 6 panels, each in series, into individual Victron MPPTs. 1 string for each side of the roof.

We run ~140vdc @10a into each Victron 150/100 MPPT, and it's been working great.


With the bypass diodes built into the panels, if we have shading due to Satellite dish, AC, or whatever else, it simply drops the volts for that panel and continues to operate normally.

This allows us to use 10awg from the panels to the MPPT.

We can charge our batteries at almost 100a @14vdc per MPPT.

Sometimes we even exceed our rated wattage as shown here where we are making almost 25% more.




Panels in series works great and I wouldn't worry about 'shading'.

You don't spend good $ on building a solar system to simply park in the shade.
Aren't you worried about putting 140V into a 150V controller when the temperature drops?
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Old 09-01-2019, 09:45 AM   #12
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The advice to use parallel is based on older panel designs prior to bypass diodes being common. And back then PWM controllers were often used as MPPT was a costly upgrade.

Using present day commodity tech the way to go is series.

But it will take a long time for old ways to change, just like when radial tires couldn’t be rotated. It took two years to fix the issue and twenty years for the information to penetrate.
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Old 09-01-2019, 10:04 AM   #13
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Variations in panel manufacturing from purity of chemicals used for the cells to individual cell connections, etc and type of panel all impact a panel's power production. Not all panels are created equal. Some panels do much better in low light or shaded conditions than others. Keep in mind that are multiple manufactures marketing double sided panels. Yes the back side also produces power at a lower output level.

Exactly which panels you can use depends largely on the roof layout. I used three 350 watt mono panels from Silfab and have had great success with them. Even while parked under trees. My batteries are almost always back to 100% by 10 am. I have never seen what this system is capable off on a clear day at solar noon. Only once did the 100% mark go past noon, made it at 1pm. There had been snow on the roof for much of the morning. I wired them in parallel, each panel produces a measured 44 volts. I have a builtin volt meter attached to the input side of the controller and can see real output anytime. These are large panels and will not fit on many RV roofs.

My advise is to do your own research on line.
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Old 09-10-2019, 10:15 PM   #14
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Quote:
Originally Posted by creativepart View Post
IF I were you... I'd remove the Zamp 3-port box entirely and create a new connection box with bus bars. That way you can ditch the silly little Zamp SAE connectors and connect your panels directly to bus bars.

OR change everything to MC4 connectors and wire up series or parallel MC4 wire looms.

I'm using the Zamp 3-port and I check my wires every time I'm on the roof. Honestly, it feels like the SAE connectors are barely holding on. Though I admit I've never found one that has dislodged. MC4 connectors seem much more robust and secure.

There are tons of YouTube videos showing large RV solar panel systems wired into waterproof boxes with bus bars inside if you need to see how this is an improvement.
One other lesser-known piece about the Zamp combiner is that some models (2018 and earlier) have an auto-resetting breaker inside thatís only rated to 14 VDC maximum. Datasheet: http://www.cooperindustries.com/cont...ortstop_CB.pdf
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