Simple Airstrteam Series/Parallel Solar System

[KSA63]

I have been considering a simple 400W Series Parallel solar system for a couple of years. In all of the information that I have researched online I was able to figure out what I needed and how it needed to be wired but I was unable to find a simple wiring diagram for what I am planning to do. I have put together a drawing/diagram myself and would like to know if I have made any mistakes or if I have left off any critical components that I will need.


Thanks
Kevin

[AirMiles]

Originally Posted by KSA63

I have been considering a simple 400W Series Parallel solar system for a couple of years. In all of the information that I have researched online I was able to figure out what I needed and how it needed to be wired but I was unable to find a simple wiring diagram for what I am planning to do. I have put together a drawing/diagram myself and would like to know if I have made any mistakes or if I have left off any critical components that I will need.


Thanks
Kevin

Looks good to me. The only difference between my installation and yours is that I used a switch on the prewire before the solar controller where you have a 40A breaker. Yours will work fine with the breaker and is probably better because we found there was no breaker in the last Zamp Rooftop Box that was removed. You may want the breaker on the battery side of the solar controller closer to the solar controller.

[KSA63]

Thanks Airmiles,
Just gathering the parts now. I have the 4 Renogy Panels the Victron 100/50 and the BMV-712. Ordering the bits and pieces and trying to decide on mounting hardware for the panels. The mounting brackets are likely the hardest thing of all to get right. I like the AM solar solution but at $120CAD per panel (Amazon) they are a tad over priced. I only paid $105CAD for each panel. How can mounting brackets be worth more than the panels?

[AirMiles]

I feel the same way about the AmSolar mounting bracket prices, but I really like them. Some people have been happy with the Renogy Curved mounting brackets which I think are much cheaper. Others have made their own brackets out of 2" aluminum angle stock. I'm not good at cutting aluminum and making it look professional, so I just bit the bullet and bought the AmSolar mounts.

[Kalashnikov]

Any reason you're going with 10ga wire OUT of the victron controller? I'd go with something a little fatter (eg 6 gauge)

[HiHoAgRV]

One suggestion based on my experience with a series/parallel system like yours, rewire the panels differently. When a shadow crosses one of the series panels, it limits the output of both panels. My typical shadowing is when parked in a non-East/West position so a single tree branch/pole/... kills everything. Wire both forward panels in series and both rear panels in series. A single shadow only kills one set.

Attached shows how this happens

[DntheRoad69]

Thank you for sharing. I am still in the planning stage. Your plans help me visualize the system

[AirMiles]

Originally Posted by HiHoAgRV

One suggestion based on my experience with a series/parallel system like yours, rewire the panels differently. When a shadow crosses one of the series panels, it limits the output of both panels. My typical shadowing is when parked in a non-East/West position so a single tree branch/pole/... kills everything. Wire both forward panels in series and both rear panels in series. A single shadow only kills one set.

Attached shows how this happens

I too put my panels in series on opposite sides versus on the same side. I think its better because both sets of panels will always be receiving equal sunlight, no matter the position of the sun, which should always keep voltage, watts and amps similar on each set.

I think the same idea would work in HiHoAgRV's shading example. If a shadow went across both rear panels with them wired in series-parallel as in the example HiHoAgRV used, you would not lose all power. You would lose 1/2 the power just like if they were wired in series-parallel on each side of the Airstream. I've done this test to prove it in the past. Here are my results:
https://www.airforums.com/forums/f44...ml#post2242341

Notice on the screen with 57W of output how the voltage dropped from 30V to 14V? That is what happened when three of the four series-parallel connected panels were covered with a towel. I did not lose all four panels, I lost three. If two panels were covered, either both from one series pair or one from each series pair, I believe you would get 1/2 the total array output either way. I think the voltage would drop from 34V to 17V if one panel from each series pair was covered. I think the voltage would be 34V but the watts would cut in half if both panels from one series pair were covered. Either way, you would get 1/2 of the potential battery charging.

I know this is a mind bender and I apologize if I have the Volts, Watts, and Amps mixed up. Bottom line is that I am certain it would make no difference in the charging of the battery how the shadow went across two of the four panels. Even if all four panels were configured in parallel, you would still lose two of four panels with two shaded. The only time 400W of series-parallel loses to full parallel is when one panel gets completely shaded. If two panels get shaded, no matter which two, you will lose output from two panels. If three panels get shaded, no matter which three, you will lose output from three panels.

Here is another "real life" shading test I did using tree shade instead of towels: https://www.airforums.com/forums/f44...ml#post2102863 The shading results in this test with real tree shade were less dramatic than those using towels. Real tree shade has less effect on output than towels because the MPPT solar controller can adapt to partially shaded panels better than completely shaded panels.

[KSA63]

Originally Posted by Kalashnikov

Any reason you're going with 10ga wire OUT of the victron controller? I'd go with something a little fatter (eg 6 gauge)

Thanks for the observation. One Change I have already made is to go with 10ga wire on the roof (haven't updated my drawing) and since it will make little (if any) difference in output from the controller by using the same wire for the few feet it will need to travel, I will just order enough 10ga to do it all. By the way, I had been reading your struggles with your 100/50 and hope I do not have the same issue. Glad you got it sorted.

Originally Posted by HiHoAgRV

One suggestion based on my experience with a series/parallel system like yours, rewire the panels differently. When a shadow crosses one of the series panels, it limits the output of both panels. My typical shadowing is when parked in a non-East/West position so a single tree branch/pole/... kills everything. Wire both forward panels in series and both rear panels in series. A single shadow only kills one set.

Attached shows how this happens

HiHoAgRV, thanks for your contribution. I had thought of shadow losses as being an issue and will think a bit more about it before doing the installation. I am not too concerned about maximum solar harvest as I believe that 400W will be more than I need most of the time. If I need to address a problem I can rewire or add two more panels down the road.

Originally Posted by DntheRoad69

Thank you for sharing. I am still in the planning stage. Your plans help me visualize the system

DntheRoad69, I'm happy they could help you. I had trouble visualizing the system until I put it into the drawing.

Originally Posted by AirMiles

I too put my panels in series on opposite sides versus on the same side. I think its better because both sets of panels will always be receiving equal sunlight, no matter the position of the sun, which should always keep voltage, watts and amps similar on each set...

Airmiles, I think you are saying that you feel the shading losses may be similar in either situation. I tend to agree and will likely wire the panels as I have drawn them.
EDIT: On reading again, it seems that I misread your answer and in fact you agree with HiHoAgRV's view. I will take a look at rewiring to suit.

[Hermes]

Why not simply wire each panel in parallel? Running a 10 ga wire from each panel to the combiner box is no more complicated than running a wire from one panel to the next then to the combiner box.

I must be missing something... In my full parallel setup, I only need one of my five panels to be unshaded to maintain the battery bank in "normal" usage and sunshine conditions, and I don't care which panel that is; this would not be the case with a series-parallel setup.

If I was covering my house or cottage with solar panels, it would be a different matter. For an RV, given their mobility and the environments in which we park them, I want to maximize my options.

[KSA63]

Originally Posted by Hermes

Why not simply wire each panel in parallel? Running a 10 ga wire from each panel to the combiner box is no more complicated than running a wire from one panel to the next then to the combiner box.

I must be missing something... In my full parallel setup, I only need one of my five panels to be unshaded to maintain the battery bank in "normal" usage and sunshine conditions, and I don't care which panel that is; this would not be the case with a series-parallel setup.

If I was covering my house or cottage with solar panels, it would be a different matter. For an RV, given their mobility and the environments in which we park them, I want to maximize my options.

Hi Hermes, I was looking at all options and decided on series-parallel for a few reasons. One of my main reasons was that I wanted to get the most out of the Airstream Pre-wire. Since that Pre-wire is 10ga then going parallel with all four panels would potentially result in some higher currents and loss. For instance at Vmp or 17.9 Volts and Imp of ~22.9 Amps the loss in a 50 foot circuit will be 12.75% or >2.25Volts. Over that same circuit the losses in the 35.8 Vmp and 11.4 Imp series parallel arrangement would be only 3.2% or 1.14 Volts.

Using the Victron MPPT solar charge controller will make good use of the higher Voltages to put more energy into the battery than the same system operating in a Parallel arrangement. At least I hope it will.


Kevin

[AirMiles]

Originally Posted by KSA63

Airmiles, I think you are saying that you feel the shading losses may be similar in either situation. I tend to agree and will likely wire the panels as I have drawn them.
EDIT: On reading again, it seems that I misread your answer and in fact you agree with HiHoAgRV's view. I will take a look at rewiring to suit.

I was not agreeing with HiHoAgRV's view. I was trying to say it doesn't matter how a shadow would cross two panels because you will lose two panels in all configurations (series-parallel on the same side of the Airstream, series-parallel on opposite sides of the Airstream, or four parallel configured panels).

I do think there is a benefit to having the opposing angled panels wired in series because then both sets will be getting equal sun. But then in a case where shading is expected from a dual A/C Airstream (like Kalashnikov with 600W) I think it makes sense to have the series-pairs on the same side of the potential shading. In Kalashnikov's case, there will always be 400W unobstructed no matter how the sun is angled. If Kalashnikov used opposing angled series-pairs, he may end up with shading on two series connected panels. Then the third series-pair would have much higher voltage than the other two series pairs. At that point, the MPPT controller would have to decide if it was better off with only using the 200W from the unobstructed series pair or reduce that pair to match the other two obstructed series pairs. If it chose to use the unobstructed series pair, there would only be 200W of potential. If it chose to reduce the unobstructed pair to the other two obstructed pairs potential, it would only be 300W of potential. Therefore, Kalashnikov's decision to keep potentially shaded pairs on the same side is preferred because it will always result in 400W of potential in the worst case A/C shading scenario.

Again, this gets complicated. But on a 400W series-parallel system on a 25' Airstream it will not make any difference how you lay out your series pairs. If one panel gets blocked you will lose two. If two get blocked you will lose two, if three get blocked you will lose three. If four get blocked you will lose all four. If you choose to go 400W in parallel, when one gets blocked you will lose only one. But I would still use series-parallel because I have never had an issue with shading and Victron recommends a series-parallel configuration when using 100W panels.

[pteck]

To the KSA63, I would take any series advice with a huge grain of salt.

There's individuals on this forum that continue to push their perceived "enlightened" agenda for series/parallel. Against example based evidence, against professional installation best practices, against engineering supported tradespace of first principles.

All of which support that all parallel installations are what is recommended for an RV based installation, where shade handling is the name of the game. Series installations are only preferred on static house based installs where shade is well controlled, with longer wiring runs.

Take the below link as a strong example of what you might be optimizing for.

https://www.airforums.com/forums/f37...ay-206230.html

Series/parallel is optimizing for transmission. Materially representing 1 watt, which is much than 1% of production, on a good day when there's excess production anyways.

Versus shade handling on a compromised day, where series setups will have upwards of 10%+ loss. Situations where every watt of production counts.

Which is why parallel is a best practice for RVs.

If one does want to optimize for transmission on larger arrays, then pull larger gauge wire instead of using the factory pre-wire. IIRC, 2019 and on Airstreams already have the advantage of larger 8 guage pre-wire. Then it's a win win.

[AirMiles]

I am not going through this same argument with Pteck again. Read through the Solar Show and Tell thread: https://www.airforums.com/forums/f44...ll-181608.html . As Pteck said, "Series/parallel is optimizing for transmission." Exactly, transmission efficiency is what is needed to use the 10 gauge factory prewire and achieve the same efficiency as a parallel configuration with 4 gauge wire.

I have installed a 400W series-parallel configuration and a 600W series-parallel configuration on two different Airstream prewires. I have posted over 250 days of use from these two installations, in 30 day continuous periods, to document how well this configuration works for me. I wish more people would post 30 day performance data so we could compare series-parallel configurations to full parallel configurations. My data, and the attached graph, shows that my inefficient wet-cell golf-cart batteries float nearly every day with the series-parallel configuration. If the batteries float every day with series-parallel on the factory prewire, why go through the added effort and expense to install 4 gauge wire? The dark area on the top of each bar in the graph represents the time spent in float mode each day.

[HiHoAgRV]

I guess I should have been more succinct. A quote from Renogy (who’s panels I have)

“When panels are wired in series, they all in a sense depend on each other. If one panel is shaded it will affect the whole string.”

And I have observed this in my setup.

This I suggested that side by side panels (across the width of the roof) be the ones in series. Then when a tree limb/power pole shades across the roof, only one set of series panels is affected. The remaining 2 in series are still at full steam.

It’s really frustrating to see one shadow 6” wide slowly travel down the entire length of my array and reduce my 400w system to a couple of amps.

I have not had a campsite with a shadow from the front (that’s where the driveway is) or the rear do this but I’m sure your mileage will vary.

[cmell]

That's a great diagram you made. My only comment (solar is my day job) is that usually the plastic MC4 connectors coming off the back of a PV panel are such that the male connector is + and the female connector is -. So it looks to be backwards in your drawing.

HOWEVER, to confuse it further... When you order MC4 connectors, they are actually named by the metal pin you crimp onto the wire. And the male pin happens to go into the female-looking plastic connector. The female pin goes into the male-looking plastic connector.

So on a traditional solar module you would order a "Male" MC4 to match up with the positive lead (even though it too looks to be male at first glance).

Hope that helps someone avoid some confusion.

[gator.bigfoot]

You might want to consider running 2 sets of 10 gauge wire and then 2 controllers. Wire 2 of the panels in parallel and the other 2 in parallel to each controller. Then the controllers can work independently based on the shading they receive. You can then also purchase less expensive controllers since you don't need as much power, but you will need 2. But you will also save on the cheap 10 gauge wire. Especially if one is already installed.

As far as brackets go, I made my own out angle iron, but instead of iron it's made out of aluminum. I just went to HD and purchased a 18" length or so from their hardware section and then cut them into 4" lengths. The 3m tape sticks it to the roof really well and the sikaflex 221 around the base will prevent it from getting water under. Drilling the holes in the brackets ahead of time and fastening the brackets to the panels makes short work of it. Then it's just positioning the panels and marking the locations with tape. Then clean the area where the brackets go and peel the other side of the tape off and place the panels. Then caulk around the feet.

[pteck]

Originally Posted by AirMiles

I am not going through this same argument with Pteck again. Read through the Solar Show and Tell thread: https://www.airforums.com/forums/f44...ll-181608.html . As Pteck said, "Series/parallel is optimizing for transmission." Exactly, transmission efficiency is what is needed to use the 10 gauge factory prewire and achieve the same efficiency as a parallel configuration with 4 gauge wire.

I have installed a 400W series-parallel configuration and a 600W series-parallel configuration on two different Airstream prewires. I have posted over 250 days of use from these two installations, in 30 day continuous periods, to document how well this configuration works for me. I wish more people would post 30 day performance data so we could compare series-parallel configurations to full parallel configurations. My data, and the attached graph, shows that my inefficient wet-cell golf-cart batteries float nearly every day with the series-parallel configuration. If the batteries float every day with series-parallel on the factory prewire, why go through the added effort and expense to install 4 gauge wire? The dark area on the top of each bar in the graph represents the time spent in float mode each day.

Lots of data does not stand alone. Logical premise is required for any accurate conclusion to be drawn.

Your data shows nothing more than that your system works.

In your same thread, I've shown you how my comparable 400W system, wired in all parallel, on factory pre-wire works better. Producing a higher watermark of production than any single day in your months of data. Perhaps that's why your felt the need to upgrade to 600W, because your 400W system doesn't perform in difficult scenarios.

Just as the link I showed above that, with tests from MandN showing that parallel works better.

You'll conveniently ignore all this and continue to espouse serial enlightenment, to the detriment of the community.

[Hermes]

Originally Posted by KSA63

One of my main reasons was that I wanted to get the most out of the Airstream Pre-wire. Since that Pre-wire is 10ga then going parallel with all four panels would potentially result in some higher currents and loss. Kevin

Thanks Kevin, that explains it.
Unlike what I posted in a previous thread on this topic (https://www.airforums.com/forums/f44...at-205209.html), after putting my thinking cap back on, if I were in your shoes it would make sense to use the 10 ga pre-wire and see if a series-parallel setup works for you; you can try it for a season or two.

If it doesn't, you can always rewire your panels in parallel to a combiner box and run two 4 ga wires through the refrigerator vent sidewall and down to your MPPT controller and battery bank. But it is obvious that the AS folks didn't have 4,5,6 panels in mind when they pre-wired with 10 ga.

[Kalashnikov]

Originally Posted by Hermes

Thanks Kevin, that explains it.
Unlike what I posted in a previous thread on this topic (https://www.airforums.com/forums/f44...at-205209.html), after putting my thinking cap back on, if I were in your shoes it would make sense to use the 10 ga pre-wire and see if a series-parallel setup works for you; you can try it for a season or two.

If it doesn't, you can always rewire your panels in parallel to a combiner box and run two 4 ga wires through the refrigerator vent sidewall and down to your MPPT controller and battery bank. But it is obvious that the AS folks didn't have 4,5,6 panels in mind when they pre-wired with 10 ga.

These days the prewire is 8ga, wire itself seems to be of very high quality.



I have three sets of [100+100W] panels, I view them as three parallel 200W "panels." On set on each side (and both of those panels shaded by an AC, I have two), one set in the front (no shade whatsoever.) I don't think going fully parallel across all 6 panels would have made any difference.