Solar- Series for Higher Voltage vs Parallel Lower Voltage

red31 wrote:

BFL13 wrote:
I keep reading how you do better with the higher voltage in series unless there is shading.

stop reading!

yup, it's one of those "it depends" situations. first look at the efficiency curves on the controller, since it's likely a MPPT controller, ones I've seen have a varying efficiency as the panel voltage deviates from battery voltage. On mine max efficiency is when panel and battery voltage are a near match . When they are far apart there is a noticeable decrease in efficiency, more than one would often get from lower cable IR losses from series.

and then the panels need to be matched for best series performance as well. mixing panels can make series worse than parallel. Usually the max current will be limited by the lowest panels current. In parallel, each panels current adds to the total. But then mismatched panels with different Vmp can effect overall efficiency as well.

My experience is that when I have 150Ft portable runs with #10 wire AND 480W of panels AND well discharged batteries, AND no shading, AND bright sun series wins noticeably. Otherwise parallel is less hassle with shade and neither has enough benefit to dominate decisions, but parallel seems to be more forgiving.

BFL13 wrote:
I keep reading how you do better with the higher voltage in series unless there is shading.

stop reading!

Phil, yes there are days without much sun. After the sun returns, in theory you could work your way back to "full" by having a surplus every day, doing some "management". Phooey on that! Out comes the Honda 3000 and two PowerMax converters (100ampADJ and a 55ampADJ) and get caught up in about two hours (50-90) and then let solar do the rest so we are back to "normal" the same day.

It is better for the batts not to leave the batts not fully charged over several days until you catch up with just solar, so get them back up as high as possible as soon as possible (within reason of course)

Phil, you need a little cargo trailer to tow along. You can store your Honda and a couple panels in that. Add a big inverter and a couple batteries. Now you have your very own power station. Plug the shore power cable into it. For extra points make that trailer a station wagon toad. Now you can take the power station to town to buy groceries without having to break camp with the motor home.

BFL13 wrote:
It would be different for a full- timer on solar all year, but not for me with the 5er using solar only in the summer. We can be 12v pigs with the big inverter and microwave. toaster, kettle, used like crazy, and have no problems at all in the summer with about 230 watts in the tilted twirler. No need for more watts.

Thanks for your excellent run-down on solar issues and considerations!

So - even during extended summer rainy days - you think "you can't have too much solar" doesn't apply to you? I remember once when stationed in Utah we had a freezing sleet storm with dark daytime skies in AUGUST ... so you never know what Mother Nature is going to throw your way!

If I didn't want full-time access to my RV's roof area, I would really load it up with panels to both - keep the interior cooler in the summer (via the solar panels providing an air-insulating buffer between them and the roof surface), plus keep the batteries continually full so we could use electricity with impunity 24/7 regardless of daytime sun conditions.

P.S. Do you have a site reserved along the August Path of Totality so you can get a few minutes of daytime data on your solar panels' energy harvesting capability with "no sun"? :)

You are the man BFL13! Thanks for sharing.

Based on this "lesson learned" and after some thinking, I have decided to revert to what I had a couple years ago for the 5er in summer for the rest of this year, and dump the three 100s for that job.

I am back to the single 255 panel in the tilting twirling ground mounted contraption as before, which was fine for enough AH a day. I have put the three 100s on the truck camper instead of the 255w single.

I can get the "value" of the 300 over the 255 (by "over-panelling" but with the three lying flat) that way more likely in the scenarios with the TC where and when it goes. The 255 is easier to handle physically as a portable when setting up/breaking down for use with the 5er. It is also a lot easier to haul the three 100s up top on the TC one at a time than that heavy 255. ( I have them in a sort of tray up there so I can take them down when parked at home in winter when tree branches might fall on the panels)

As I have stated before, contrary to those who say you can never have too much solar, I have found that I can have too much. We only need so much a day, and when I have taken along more solar for a more complicated set-up, all it does is get me "done" somewhat earlier in the day, but to no advantage really.

It would be different for a full- timer on solar all year, but not for me with the 5er using solar only in the summer. We can be 12v pigs with the big inverter and microwave. toaster, kettle, used like crazy, and have no problems at all in the summer with about 230 watts in the tilted twirler. No need for more watts.

I screwed up getting a second, higher intake voltage MPPT controller just so I could get the "benefit" of going series with the three 100s. Waste of money. Oh well, same money as a tank of gas for the truck, and did learn something, so not hurting too badly.

Maybe somebody can save a dollar or two by reading how I screwed up, who knows? Anyway, it should be of interest to the usual suspects. :)

BFL13 wrote:
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" ?

One correction to what you said - ".... since you (at least I) get the same ENERGY either way ...".

With your fat wires ... IMHO stay in parallel with your panels so that you get redundancy in energy output - in that if one panel gets shaded you still get the full, or nearly the full, energy output from the remaining array of panels that they are capable of. With all your panels in series, the energy capability of the array can be drastically reduced.

I do not have solar on our RV ... I just applied electrical principles to come to that conclusion. The Solar Magic power optimizer for solar panels in series was supposed to help get around this limitation of what a shaded panel in a series array could do to the rest of the array's output capability, but I don't believe it lived up to it's claims.

It's totally

Transmogrificating

Yes it's a real word in a verb conjugation.

Ok.lol.. just thought I was going to learn a new word. All I could think of was "measurements", but instruments makes more sense.

2oldman wrote:

Searching_Ut wrote:
I learned when I first got into testing and evaluations decades ago was to trust the interments.

What is that word.. interments?

To be honest, I didn't have a clue what the word was until you pointed it out, and I googled it to see. I would guess it got there as a result of my fat fingering the word instruments, and spell checking deciding the word needed buried. Of course in my limited version of proof reading, I evidently saw the word I expected to see rather than what I wrote. (How's that for an attempt at recovery?:S)