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Old 10-08-2019, 08:57 PM   #1
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In series or parallel

I have two 100 watt solar panels and a mppt charge controller. This is to charge a 12v battery. Should I wire the panels in series or parallel?
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Old 10-08-2019, 09:05 PM   #2
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Parallel for sure.
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Old 10-08-2019, 09:27 PM   #3
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Parallel for sure.
Why? I am thinking (watch out) that if the panels are not getting much sun then in series may provide enough voltage. Won’t the mppt controller handle the high voltage of in series full sun?
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Old 10-08-2019, 09:39 PM   #4
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if the panels are not getting much sun then in series may provide enough voltage.
This is a fallacy promoted by non-technical individuals on these boards. Even when disproved, they continue the spread of false information.

Truth is, all panels are rated at a nominal voltage higher than system voltage. i.e. 19V vs 12V system voltage.

If there's insufficient sun or shade enough that a panel is not producing near nominal voltage, there's simply not enough solar energy to be had to produce meaningful watts/power. Series connected panels won't change that fact.

That said, in a 2x panel setup, it won't matter as much if it's series or parallel with an MPPT controller, yet parallel still has a distinct edge in overall production.
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Old 10-09-2019, 05:24 AM   #5
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pteck is correct. Shoot me a PM if you like. I would be glad to speak with you on the phone.
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Old 10-09-2019, 08:59 AM   #6
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Never mind that the Victron owners manual recommends using a series connected pair when using 100W panels for the very reason the op asked the question.

I use series connected pairs with my Victron MPPT controllers as recommended by the manufacturer because it provides the “highest controller efficiency”. I’ve documented hundreds of days of actual usage throughout the Solar Show and Tell thread. It works very efficiently as the manufacturer suggests.

Will parallel work with 100W panels? Yes very well as documented by Bigventure in the Solar Show and Tell thread. http://www.airforums.com/forums/f448...ml#post2296220

Both will work, but series pairs of 100W panels will work more efficiently than full parallel configurations on Victron MPPT controllers.
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Old 10-09-2019, 09:09 AM   #7
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Efficiency

Yes. If operating at a higher (in series) voltage to the MPPT controller, there is higher efficiency and less voltage drop through wiring which the Victron can convert to the batteries.

This assuming your MPPT controller open circuit input voltage input is compatible with the series panels output voltage.
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Old 10-09-2019, 09:19 AM   #8
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Yes. If operating at a higher (in series) voltage to the MPPT controller, there is higher efficiency and less voltage drop through wiring which the Victron can convert to the batteries.

This assuming your MPPT controller open circuit input voltage input is compatible with the series panels output voltage.
Which results in higher Amps of battery charging per Watt of input. All day everyday.

Now the parallel side will bring up shading. First, no solar panel works well in the shade. Choose to park in the sun. Any time shading was enough of an issue to stop my series-parallel configuration from fully charging my batteries, a parallel configuration would not have made the difference. Again, all documented in the Solar Show and Tell thread.

This whole topic has been beaten to death in many threads, including the Solar Show and Tell thread. I recommend reading through that thread.
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Old 10-09-2019, 09:30 AM   #9
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Hi

First question would be - just what controller do you have? The term MPPT covers a whole lot of devices. A "12V" panel can indeed get up near 30V. A pair of them in series can hit around 60V. (yes, it has to be pretty cold out ...) If your controller is "only" rated for 50V ... that's not a good thing.

At least if I'm putting things together, anything that hits 80% of a "max voltage" rating is not going into the system. That's a personal choice, but it's also my money being spent. A "75V" controller is right at that limit with two panels.

The magic math:

-0.5% per degree C (yes you could get more exact than that).

Voc at 25 C 23V

Cold = -25C

Delta = 60C

60 x 0.5 = 30%

23 x 1.3 = 29.9V

Yes those numbers are picked to make the math easy. The -25C number is about as cold as
it gets in my part of Pennsylvania.

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Old 10-09-2019, 09:48 AM   #10
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AirMiles,

I won't play this game with you again, as you are bent on "enlightening", including every professional contractor out there that installs solar panels for RVs in all parallel fashion. Because you assume a single detail consideration for static home installs where shade is well controlled to be a factor against 1st order considerations for a mobile installs where shade handling is the name of the game.

This is the salient point:

From your other thread, your series-parallel systems have always struggled to show significant daily production. Your 400W system routinely tops out around 1.2kWH in daily production. Your 600W has only shown a high water mark around 1.54kWH.

Whereas my all parallel 400W system regularly produces over 1.7kW even against shade.

Even over factory pre-wire which is why you considered series-parallel originally.

It's easy to be confused with the amount of trade space there is in optimizing volts here or amps there. There's no single number that matters more than daily production over varied situations and your data points have shown your series-parallel setups are not showing its full potential.

As I mentioned in the other thread. You are well written and a good influencer. Don't be a modern day youtube star where substance is lacking. You have a responsibility to be factually correct when you have the ear of many.
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Old 10-09-2019, 10:06 AM   #11
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Given your question, I would have a professional install it.
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Old 10-09-2019, 11:48 AM   #12
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Originally Posted by pteck View Post
AirMiles,

I won't play this game with you again, as you are bent on "enlightening", including every professional contractor out there that installs solar panels for RVs in all parallel fashion. Because you assume a single detail consideration for static home installs where shade is well controlled to be a factor against 1st order considerations for a mobile installs where shade handling is the name of the game.

This is the salient point:

From your other thread, your series-parallel systems have always struggled to show significant daily production. Your 400W system routinely tops out around 1.2kWH in daily production. Your 600W has only shown a high water mark around 1.54kWH.

Whereas my all parallel 400W system regularly produces over 1.7kW even against shade.

Even over factory pre-wire which is why you considered series-parallel originally.

It's easy to be confused with the amount of trade space there is in optimizing volts here or amps there. There's no single number that matters more than daily production over varied situations and your data points have shown your series-parallel setups are not showing its full potential.

As I mentioned in the other thread. You are well written and a good influencer. Don't be a modern day youtube star where substance is lacking. You have a responsibility to be factually correct when you have the ear of many.
The limiting factor in my configuration is the battery. It’s difficult to post over 1.5kWh daily production with a 235AH battery and while using about 100AH per day from it.

Since installing my 600W system, I’ve either been parked under significant tree canopy and/or overcast conditions. And again I will be using my old 235AH batteries. Don’t worry though, I’m sure I’ll be posting some 600W real-time production numbers when the conditions are right, a bright sunny day with a high real-time Amp draw.

Here’s what my 400W series-parallel solar array could do when needed by the batteries or real-time Amp draw. 403W and 30.1A of charge - the limit of the Victron 100/30 Controller. If that’s struggling, I’ll take it!
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Old 10-09-2019, 12:24 PM   #13
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I like to provide real-time information. So I went inside my Airstream, turned on the DC refrigerator, a hairdryer on the inverter, and all lights, fans, and radio. Here’s what my 600W series-parallel configuration can do under fairly cloudy conditions. Not bad for real-time information - 408W and 31.4A of charge. See first two photos.

The best I’ve gotten, in the 30 days I’ve had 600W of solar, was 491W of production while sitting in storage with a fairly drained battery. See last two photos.
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Old 10-09-2019, 12:42 PM   #14
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I like to provide real-time information. So I went inside my Airstream, turned on the DC refrigerator, a hairdryer on the inverter, and all lights, fans, and radio. Here’s what my 600W series-parallel configuration can do under fairly cloudy conditions. Not bad for real-time information - 408W and 31.4A of charge.
Hi

Worth noting on that screen is the ~30V into the controller. With a parallel setup, you would be at 15V. That gets into "struggling" range for most controllers. Even more so if they are trying to put out ~14V. Net result typically would be a higher operating point and likely a lower output current.

You *could* design a box that didn't work that way. The bottom line is that they don't do that. They all run down conversion (buck) converters. That means they have a finite "headroom" requirement.

More or less - on that day, under those conditions, with that hardware, series wins. On another day, under different conditions .... who knows.

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Old 10-09-2019, 01:52 PM   #15
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The limiting factor in my configuration is the battery. It’s difficult to post over 1.5kWh daily production with a 235AH battery and while using about 100AH per day from it.

Since installing my 600W system, I’ve either been parked under significant tree canopy and/or overcast conditions. And again I will be using my old 235AH batteries. Don’t worry though, I’m sure I’ll be posting some 600W real-time production numbers when the conditions are right, a bright sunny day with a high real-time Amp draw.

Here’s what my 400W series-parallel solar array could do when needed by the batteries or real-time Amp draw. 403W and 30.1A of charge - the limit of the Victron 100/30 Controller. If that’s struggling, I’ll take it!
Negative. Your assumptions again are misleading you.

I have the same 2x 6V batteries and I consistently see more production than your setup. With lower end electronics.

You again presume shade is the exception. Who wants to camp in the open when shade is available. Shade is the norm and a system should be setup and optimized to accommodate this scenario. Not to optimize for some secondary or tertiary concern.

Who care's what peak output you make. Slow and steady is the name of the game in solar. It's not about what the system will do wide open with ideal sun and alignment. The test has and always will be what the system will do on compromised days with weather and shade. Which is why it's what should be optimized for! When the sun is out, even those with minimal solar will be
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Old 10-09-2019, 05:09 PM   #16
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Negative. Your assumptions again are misleading you.

I have the same 2x 6V batteries and I consistently see more production than your setup. With lower end electronics.

You again presume shade is the exception. Who wants to camp in the open when shade is available. Shade is the norm and a system should be setup and optimized to accommodate this scenario. Not to optimize for some secondary or tertiary concern.

Who care's what peak output you make. Slow and steady is the name of the game in solar. It's not about what the system will do wide open with ideal sun and alignment. The test has and always will be what the system will do on compromised days with weather and shade. Which is why it's what should be optimized for! When the sun is out, even those with minimal solar will be
Is it that you produce more wattage or is it that you consume more?
A critical detail of the Victron "show and tell" is consumption vs. production.
When I was boon docking with heavy inverter usage I could have increased my daily usage by another 1/3 I bet had I been at the trailer to consume more watts. Being gone all day limited my production to what I could actually consume, remember production is both battery charging and live loads.
On my campground trips my daily production was a 1/4 of what I "produced" boon docking but in reality I just used less...

It's all good banter but with out back to back real time testing I can't say which way is better. Bigger cables win either way and my family friend/camping partner EE didn't understand the series/parallel arrangement at all and proclaimed straight series would be be more beneficial than the hybrid method. I didn't have a educated rebutal...
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Old 10-09-2019, 05:43 PM   #17
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I bet by now the original poster is sorry he asked.
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Old 10-09-2019, 05:55 PM   #18
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I sure hope that now that I have three 200W panels in parallel (Same as six 100W panels in series-parallel) that I can park in the shade and produce 1.7kWh of power. That is going to be awesome!

Anyone who has solar knows that production dwindles as batteries get charged. My batteries are in absorption stage before peak solar hours when given enough sunlight. When there’s no sunlight, there precious little production. The only way I can show my system’s capabilities is to force production with real-time use.

Again, I share all my production results, one month at a time, on the Solar Show and Tell thread. When I have an unusually good or bad day of solar production, I post specifics about that day with pictures and performance results. Please start posting your good, bad, and ugly results so we can all learn from each other.

One of us is posting data, pictures and details and the other is posting snarky remarks and opinions. Let’s see everyone’s solar production data with pictures so we can learn something instead of just arguing.
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Old 10-09-2019, 06:04 PM   #19
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For my own education when I get to the point where we want to install 4 x 100w Solar Panels on a Globetrotter 27 and am faced with the smaller AWG of the AS solar prewire and the 3-port combiner box (unless they upgrade both before then---hint, hint, anyone listening?), does anyone know what Lewster says about it?

Or AMSolar?

When doing a 4 x 100w (or more) configuration, do Lewster and/or AMSolar run larger AWG to replace the AS factory pre-wire and replace the combiner box, or take a hybrid approach?

BTW, I'm not saying that how Lewster and/or AMSolar do it means it will be determinative in my decision, as I know others are certainly happy with their hybrid approach. But, interested to know.

Thanks.

Cheers,

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Old 10-09-2019, 06:20 PM   #20
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Is it that you produce more wattage or is it that you consume more?
Yes, it's certainly a variable and the assumption is the trailer under use. AirMiles uses his trailer a lot and posts a lot of data where you can clearly see when it's consumption limited or production limited. His best and high production watermark is lower than expected. You can peruse that data yourself. Never peaking over 1.3kWH with his 400W series-parallel system. Now he has 600W in series-parallel. With limited use, showing a high watermark of 1.54kWH.

Quote:
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I sure hope that now that I have three 200W panels in parallel (Same as six 100W panels in series-parallel) that I can park in the shade and produce 1.7kWh of power. That is going to be awesome!

Anyone who has solar knows that production dwindles as batteries get charged. My batteries are in absorption stage before peak solar hours when given enough sunlight. When there’s no sunlight, there precious little production. The only way I can show my system’s capabilities is to force production with real-time use.

Again, I share all my production results, one month at a time, on the Solar Show and Tell thread. When I have an unusually good or bad day of solar production, I post specifics about that day with pictures and performance results. Please start posting your good, bad, and ugly results so we can all learn from each other.

One of us is posting data, pictures and details and the other is posting snarky remarks and opinions. Let’s see everyone’s solar production data with pictures so we can learn something instead of just arguing.
You know fully well I've posted definitive results on multiple occasions from my own system in your thread, so you can sop pretending here. Like I said, you have a nicer system with more sophisticated electronics that paints pretty pictures.

The numbers speak for themselves. Easily 1.78kWH out of my fully parallel 400W system. On a compromised intermittently shaded day no less. I have had production in excess of this but I have to manually take pictures.

http://www.airforums.com/forums/f448...ml#post2263612
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