I keep reading how you do better with the higher voltage in series unless there is shading. With no shading I have switched my three 100w panels back and forth several times (in bulk MPPT that is 51 vs 17 volts for me), and cannot get any better amps to the battery either way.I even did the "low light" test with overcast grey sky so I was only getting about 2.5 amps at noon, and still got no difference. It was not low light enough so I could see whether you do keep getting at least some amps with the high voltage and none when in parallel as in the "story". It would be lower amps than the 2.5 I got in better light obviously, even it if were true (which I doubt), but then who cares if you are getting 1 amp instead of none? In four hours that would get you a whole 4 AH. Gosh! :)Anyway, I just couldn't make it happen no matter how many times I tried it.I did have a thought that the MPPT controller efficiency might counter any good effect from the higher voltage. The buck converter is less efficient going to a 13v battery from 51 volts than it is with less of a drop from 17v.You still get the wiring advantage of a higher panel to controller voltage by being able to use thinner wire, but that does not help me with my already fat wire in that path.I just can't see the point except for the wiring thing. If your wires are fat enough, why not just leave the panels in parallel in case there is some shading, since you (at least I ) get the same amps either way, even in "low light" ?

BFL13 wrote: but then who cares if you are getting 1 amp instead of none? In four hours that would get you a whole 4 AH. Gosh! :)I just can't see the point except for the wiring thing. If your wires are fat enough, why not just leave the panels in parallel in case there is some shading, since you (at least I ) get the same amps either way, even in "low light" ?1 amp might matter to some, not me.My coach was "solar ready" with 10awg wire from the roof to basement. For 6 panels that means higher voltage. And series wiring is so much simpler. Plus I just like doing things differently than most. You know, a bit "out of the box."

2oldman wrote:BFL13 wrote: but then who cares if you are getting 1 amp instead of none? In four hours that would get you a whole 4 AH. Gosh! :)I just can't see the point except for the wiring thing. If your wires are fat enough, why not just leave the panels in parallel in case there is some shading, since you (at least I ) get the same amps either way, even in "low light" ?1 amp might matter to some, not me.My coach was "solar ready" with 10awg wire from the roof to basement. For 6 panels that means higher voltage. And series wiring is so much simpler. Plus I just like doing things differently than most. You know, a bit "out of the box."Your high voltage is for the wiring for sure. You were sneaky in getting around the controller efficiency by going to higher voltage everything.As an aside, ISTR you had shading issues from having a panel behind another, and we discussed ways to get around that--even going to just five panels always un-shaded which might average out better over all. What was/is your work around for the shading?

First, was your battery sufficiently charged that it would always want more current (e.g. controller in bulk charging) during all your tests ?But, yea, for short wiring runs the difference may not be much, if anything - if you look at the charts some manufacturers provide, the higher the voltage input, the less efficient the controllers are. So unless the wiring loss exceeds that loss of efficiency, things might even be worse at higher voltages.The whole low light tale doesn't make any sense, and I've never heard any reasonable scientific explanation for the belief. But you're right - at such low levels the available power is mice nuts.When panels were $5+/W, maybe it made sense to spend money to eek out every coulomb. But at current prices, it makes more sense to just add another panel, space permitting. But going a step higher higher in voltage to get back 3% wiring loss but lose 2% in controller efficiency - meh. If that 1% makes a difference, you're in trouble either way.I think the best reason for higher voltage MPPT is that the large higher voltage/wattage residential panels are much cheaper per watt, if you can get them locally and not have to pay shipping.

I'm in partial shade too often to chance the, IMO, small advantage of panels in series.

Yes, the tests were all done with thirsty batteries so that was not an issue.Good to get some confirmation on my musings about all this. Another factor that might come into play is the cost of a controller that can handle the higher voltage input (at Voc ratings)I have an Eco-Worthy 20 amper that can only take in 42 volts (newer ones can take in 50v) so while the Eco-W is fine for my single 255w panel (now all in the truck camper), it could not handle three 100w panels in series at 3 x approx 23 = 69 volts that I am now using with the 5er. ( I went crazy and bought a Tracer 20 amper that an do 100 volts input so I could run the three 100w panels I got on sale --crazy, crazy, which I thought would be better than swapping the Eco-W and "wasting" my three 100s by having to leave them in parallel.)As reported, it was all bogus. I could have done just as well with the cheaper Eco-W on the three 100s by leaving them in parallel. Only good thing is I don't have to swap the controller over depending which RV we are going to use. So getting a "better" controller that can do higher voltage so you can be in series instead of parallel is bogus IMO, unless the wiring issue is driving the whole thing. At least, based on what I have learned.

Solar- Series for Higher Voltage vs Parallel Lower Voltage

28 Replies

time2roll
Nomad
Jul 28, 2017
The reason to go parallel is to use a PWM controller.
Did you do that when you switched to parallel?
BFL13
Explorer II
Jul 28, 2017
2oldman wrote:
BFL13 wrote:
As an aside, ISTR you had shading issues from having a panel behind another, and we discussed ways to get around that--even going to just five panels always un-shaded which might average out better over all. What was/is your work around for the shading?
For the small shade produced by the a/c cowling, I fashioned a 2nd footing for when it's tilted. The bottom of the panel is moved farther away from the cowling, and tilts that panel at a slightly higher angle.

My best remedy for shading is.. ta da.. don't park in the shade. :)

Yes, but ISTR your photo showed the sixth panel behind the fifth when all tilted and you got shading in that back panel for part of the day, killing output of the whole series array while that lasted.

I thought maybe just forget that 6th panel and get full amps all day from five would be more AH per day. Last heard you were going to test disconnecting that panel and see if that was true.

Or you could give that one back panel its own $15 controller and put it on a 12v battery somehow. Or sell it. :)
2oldman
Explorer II
Jul 28, 2017
BFL13 wrote:
As an aside, ISTR you had shading issues from having a panel behind another, and we discussed ways to get around that--even going to just five panels always un-shaded which might average out better over all. What was/is your work around for the shading?
For the small shade produced by the a/c cowling, I fashioned a 2nd footing for when it's tilted. The bottom of the panel is moved farther away from the cowling, and tilts that panel at a slightly higher angle.

My best remedy for shading is.. ta da.. don't park in the shade. :)
BFL13
Explorer II
Jul 28, 2017
Yes, the tests were all done with thirsty batteries so that was not an issue.

Good to get some confirmation on my musings about all this. Another factor that might come into play is the cost of a controller that can handle the higher voltage input (at Voc ratings)

I have an Eco-Worthy 20 amper that can only take in 42 volts (newer ones can take in 50v) so while the Eco-W is fine for my single 255w panel (now all in the truck camper), it could not handle three 100w panels in series at 3 x approx 23 = 69 volts that I am now using with the 5er.

( I went crazy and bought a Tracer 20 amper that an do 100 volts input so I could run the three 100w panels I got on sale --crazy, crazy, which I thought would be better than swapping the Eco-W and "wasting" my three 100s by having to leave them in parallel.)

As reported, it was all bogus. I could have done just as well with the cheaper Eco-W on the three 100s by leaving them in parallel.

Only good thing is I don't have to swap the controller over depending which RV we are going to use. So getting a "better" controller that can do higher voltage so you can be in series instead of parallel is bogus IMO, unless the wiring issue is driving the whole thing. At least, based on what I have learned.
Lwiddis
Explorer II
Jul 28, 2017
I'm in partial shade too often to chance the, IMO, small advantage of panels in series.
mike-s
Explorer
Jul 28, 2017
First, was your battery sufficiently charged that it would always want more current (e.g. controller in bulk charging) during all your tests ?

But, yea, for short wiring runs the difference may not be much, if anything - if you look at the charts some manufacturers provide, the higher the voltage input, the less efficient the controllers are. So unless the wiring loss exceeds that loss of efficiency, things might even be worse at higher voltages.

The whole low light tale doesn't make any sense, and I've never heard any reasonable scientific explanation for the belief. But you're right - at such low levels the available power is mice nuts.

When panels were $5+/W, maybe it made sense to spend money to eek out every coulomb. But at current prices, it makes more sense to just add another panel, space permitting. But going a step higher higher in voltage to get back 3% wiring loss but lose 2% in controller efficiency - meh. If that 1% makes a difference, you're in trouble either way.

I think the best reason for higher voltage MPPT is that the large higher voltage/wattage residential panels are much cheaper per watt, if you can get them locally and not have to pay shipping.
BFL13
Explorer II
Jul 28, 2017
2oldman wrote:
BFL13 wrote:
but then who cares if you are getting 1 amp instead of none? In four hours that would get you a whole 4 AH. Gosh! :)

I just can't see the point except for the wiring thing. If your wires are fat enough, why not just leave the panels in parallel in case there is some shading, since you (at least I ) get the same amps either way, even in "low light" ?
1 amp might matter to some, not me.

My coach was "solar ready" with 10awg wire from the roof to basement. For 6 panels that means higher voltage. And series wiring is so much simpler. Plus I just like doing things differently than most. You know, a bit "out of the box."

Your high voltage is for the wiring for sure. You were sneaky in getting around the controller efficiency by going to higher voltage everything.

As an aside, ISTR you had shading issues from having a panel behind another, and we discussed ways to get around that--even going to just five panels always un-shaded which might average out better over all. What was/is your work around for the shading?
2oldman
Explorer II
Jul 28, 2017
BFL13 wrote:
but then who cares if you are getting 1 amp instead of none? In four hours that would get you a whole 4 AH. Gosh! :)

I just can't see the point except for the wiring thing. If your wires are fat enough, why not just leave the panels in parallel in case there is some shading, since you (at least I ) get the same amps either way, even in "low light" ?
1 amp might matter to some, not me.

My coach was "solar ready" with 10awg wire from the roof to basement. For 6 panels that means higher voltage. And series wiring is so much simpler. Plus I just like doing things differently than most. You know, a bit "out of the box."

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Solar- Series for Higher Voltage vs Parallel Lower Voltage

28 Replies

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