Mismatched Solar Panels for Van Build

I've got a van build where I've managed to cover the roof almost entirely, but that leaves me with an interesting set of mis matched panels. I'm looking at connecting them in this way. I was wondering if anyone has any advice or improvement ideas?

Can't make sense of that.

Two rules:
All parallel strings must be the same Vmp within 10%, and entire array will have penalty of that differernce.
All panels in series will operate at the lowest current panel in the string. Put a 10A panel in series with a 5A panel, will work at 5A only.

Wow 4 different panels… with 7 panels in total…

1 200w
2 100w
2 55w
2 35w

This will be a fun problem. To get started we need to know for each panel the following specs.
Voc
Vmp
Imp
And your battery voltage and type.(example - 12v LiFePo4).

Also, have you already purchased any Solar Charge controllers? - I hope not.

The easy answer is four runs of cables going into four Victron 75/15 solar charge controllers. But with the specs from each panel we may be able to combine them in fun and interesting ways without too much of a penalty.

Also how tall and how much space is around the two other items on the roof (fan & A/C?)? How much shade will they cast on the panels?

hello,

Mixing solar panels – Dos and Don’ts​

These are all Rich Solar Mega panels...

1 200w

• Maximum Power(Pmax): 200W
• Maximum Power Voltage(Vmp): 20.4V
• Maximum Power Current(Imp): 9.80A
• Open Circuit Voltage(Voc): 24.3V
• Short Circuit Current(Isc): 10.2A
• Maximum System Voltage(Vmax): 1000VDC

2 100w

• Maximum Power(Pmax): 100W
• Maximum Power Voltage(Vmp): 19.5V
• Maximum Power Current(Imp): 5.13A
• Open Circuit Voltage(Voc): 22.8V
• Short Circuit Current(Isc): 5.44A
• Maximum System Voltage(Vmax): 1000V DC

2 55w

• Maximum Power(Pmax): 55W
• Maximum Power Voltage(Vmp): 18.7V
• Maximum Power Current(Imp): 2.94A
• Open Circuit Voltage(Voc): 22.4V
• Short Circuit Current(Isc): 3.29A
• Maximum System Voltage(Vmax): 600V DC

2 35w

• Maximum Power(Pmax): 35W
• Maximum Power Voltage(Vmp): 17.9V
• Maximum Power Current(Imp): 1.96A
• Open Circuit Voltage(Voc): 21.6V
• Short Circuit Current(Isc): 2.13A
• Maximum System Voltage(Vmax): 600V DC

Battery system is 12.8v Lithium Iron Phosphate... 3x SOK 280ah. Also have 2x 50 amp DC / DC chargers.

I understand I'm going to lose efficiency by not using multiple solar controllers, I'm hoping to find a somewhat (85-90%) efficiency combination that can use a single Victron MPPT controller... I have a MPPT 100 | 50 currently. I don't have a lot of space to add extra equipment but I could possibly if I had to.

There's not much space around the fan and AC. Fan is 1.5" higher than the surrounding panels and the AC is about 5" tall.

Rocketman said:

Wow 4 different panels… with 7 panels in total…

1 200w
2 100w
2 55w
2 35w

This will be a fun problem. To get started we need to know for each panel the following specs.
Voc
Vmp
Imp
And your battery voltage and type.(example - 12v LiFePo4).

Also, have you already purchased any Solar Charge controllers? - I hope not.

The easy answer is four runs of cables going into four Victron 75/15 solar charge controllers. But with the specs from each panel we may be able to combine them in fun and interesting ways without too much of a penalty.

Also how tall and how much space is around the two other items on the roof (fan & A/C?)? How much shade will they cast on the panels?

Click to expand...

I'd wire all panels in parallel

b33son said:

These are all Rich Solar Mega panels...

1 200w

• Maximum Power(Pmax): 200W
• Maximum Power Voltage(Vmp): 20.4V
• Maximum Power Current(Imp): 9.80A

2 100w

• Maximum Power(Pmax): 100W
• Maximum Power Voltage(Vmp): 19.5V
• Maximum Power Current(Imp): 5.13A

Click to expand...

STRING 1:

2X 100W in parallel, wired in series with 1 200W:

39.9 Vmp
9.8A Imp (limits 5.13A * 2 = 10.26A to 9.8A)

b33son said:

2 55w

• Maximum Power(Pmax): 55W
• Maximum Power Voltage(Vmp): 18.7V
• Maximum Power Current(Imp): 2.94A

Click to expand...

STRING 2:

In series with each other

37.4Vmp
2.94A

b33son said:

2 35w

• Maximum Power(Pmax): 35W
• Maximum Power Voltage(Vmp): 17.9V
• Maximum Power Current(Imp): 1.96A

Click to expand...

STRING 3:

In series with each other
35.8Vmp
1.96A

Parallel all three strings:

35.8Vmp
9.8A + 2.94A + 1.96 Imp = 14.7A

35.8Vmp * 14.7A = 526W vs. 580W rated

Or parallel all of them and get comparable results.

You aren't going to get the full output from the array, no matter how you arrange them (voltages and currents are too unmatched, all will some degree of loading on them regardless of the configuration...)
You would need to run 4 separate charge controllers with the 200w on one, the two 100w in series on another, the two 55w in series on a third and the two 35w in series on the fourth, or accept that this system will never hit its full potential...

By paralleling everything, that both lowers your daily total generation and restricts all panels to the poorest performing ones output
Doing an all parallel array will drop your total daily generated power by about 30% over using a series higher voltage system (the 100/50 needs the panels to be 5v over the battery voltage to start up in MPPT mode- with the array all in parallel, and needing 5v above the battery voltage, an all parallel system may NEVER get into MPPT mode at all, and only run as an very expensive PWM controller!!!), by putting the panels in series (or in this case a mix of series and parallel strings), it allows starting earlier and finishing later, it will actually get into MPPT mode (gaining that 30% over a PWM one), hence the smaller daily total for all in parallel over series strings...


The most practical solution imho given what you have for running the whole set on the single Victron is a mixed series and parallel system ie the 200w in series with the two paralleled 100w in one string, the two 35w in series as the second string, and the two 55w in series in a third string, then parallel the three strings, but you lose a bit of your total output doing this... (526W out of your 580w at STC or about 10% lost, running at about 36v with 14.7A out)
This is still a low voltage for the Victron 100/50 (max 100v PV input at 50A output into the battery bank) so its efficiency will suffer because of it (MPPTs really like their input voltages as high as is safely possible, the lower the PV array voltage, the poorer their efficiency is- and yours is running at only about a third of its max voltage...) a 50v 50A MPPT would have been a better choice to begin with...

The only upside with using that existing controller is you have excess capacity- maybe some 'portable'/temporary panels (100W 19.5v/5.13A same as your existing ones) hook up in the same pattern (2x 100w panels in series, and that string in parallel with the roof array- that will slightly 'overpanel' the victron (700W max on a 12v nominal battery bank) but considering the shading issues, I don't see that being an issue lol
(The 100/50 can handle substantial overpaneling, but it would only come into play on overcast days, and in this case would all have to be in the 'portable' temporary array...) more than that pair of 100w ones would be a pain and only occasionally come into play, but the extra 2 100w panels would add a noticeable increase during normal days for only the two extra panels to set up while camping and use the excess capacity up...

Bop said:

You aren't going to get the full output from the array, no matter how you arrange them (voltages and currents are too unmatched, all will some degree of loading on them regardless of the configuration...)

Click to expand...

Agree.

Bop said:

You would need to run 4 separate charge controllers with the 200w on one, the two 100w in series on another, the two 55w in series on a third and the two 35w in series on the fourth, or accept that this system will never hit its full potential...

Click to expand...

Disagree if the small penalty is acceptable.

Bop said:

By paralleling everything, that both lowers your daily total generation and restricts all panels to the poorest performing ones output

Click to expand...

This is just plain wrong. It's literally backwards. Parallel panels have minimal influence on each other only restricting to a common Vmp.

Bop said:

Doing an all parallel array will drop your total daily generated power by about 30% over using a series higher voltage system (the 100/50 needs the panels to be 5v over the battery voltage to start up in MPPT mode- with the array all in parallel, and needing 5v above the battery voltage, an all parallel system may NEVER get into MPPT mode at all, and only run as an very expensive PWM controller!!!), by putting the panels in series (or in this case a mix of series and parallel strings), it allows starting earlier and finishing later, it will actually get into MPPT mode (gaining that 30% over a PWM one), hence the smaller daily total for all in parallel over series strings...

Click to expand...

Again, this is just plain wrong. The +5V applies to Voc, not Vmp. And in order to stay in MPPT mode, it only needs to be 1-2V above battery voltage.

A Vmp of 36 isn't going to significantly outperform a Vmp of 18 EXCEPT in the earliest and latest times of day where low light prevails and you can get a performance boost to a very low number. If you want an extra 10W for the first/last 30 minutes of the day, sure.

Bop said:

The most practical solution imho given what you have for running the whole set on the single Victron is a mixed series and parallel system ie the 200w in series with the two paralleled 100w in one string, the two 35w in series as the second string, and the two 55w in series in a third string, then parallel the three strings, but you lose a bit of your total output doing this... (526W out of your 580w at STC or about 10% lost, running at about 36v with 14.7A out)

Click to expand...

Umm...

Bop said:

This is still a low voltage for the Victron 100/50 (max 100v PV input at 50A output into the battery bank) so its efficiency will suffer because of it (MPPTs really like their input voltages as high as is safely possible, the lower the PV array voltage, the poorer their efficiency is- and yours is running at only about a third of its max voltage...) a 50v 50A MPPT would have been a better choice to begin with...

Click to expand...

Again, this is just plain wrong. MPPT actually lose conversion efficiency with higher Vmp. This is usually a wash because of reduced losses due to wiring (higher voltage, lower current), but the actual MPPT efficiency is lower.

There are no reputable 50V MPPT, so referencing it as a better choice is nonsensical.

Bop said:

The only upside with using that existing controller is you have excess capacity- maybe some 'portable'/temporary panels (100W 19.5v/5.13A same as your existing ones) hook up in the same pattern (2x 100w panels in series, and that string in parallel with the roof array- that will slightly 'overpanel' the victron (700W max on a 12v nominal battery bank) but considering the shading issues, I don't see that being an issue lol
(The 100/50 can handle substantial overpaneling, but it would only come into play on overcast days, and in this case would all have to be in the 'portable' temporary array...) more than that pair of 100w ones would be a pain and only occasionally come into play, but the extra 2 100w panels would add a noticeable increase during normal days for only the two extra panels to set up while camping and use the excess capacity up...

Click to expand...

Finally, we mostly agree here. The installation as illustrated is going to have issues with shading on the rooftop panels mostly 100% of the time. The deployable ground array will play an oversized role in production as a result.

2X or 4X 100W of lightweight flexible panels in DIY PVC frames will be a quick and easy setup:

Victron itself states that the 100/50 requires a minimum of 5v above the battery to START... (on a 17.9v array voltage, on a 12.8v battery??? thats 5.1v, which a loaded PV array may not make until well into the morning, in some locations it may never reach it all day!!!) Worse, that 12.8v is itself a wrong value (it is commonly quoted as the nominal voltage, only a very deeply discharged LFP battery would be that low, 13v is closer to the correct value and that pushes the Victrons start voltage to get into MPPT up to 18v, which that 17.9v array all in parallel is quite likely to never get to all day...)

https://www.victronenergy.com/media...0-30__100-50/en/technical-specifications.html
Having measured, repaired and used MPPT charge controllers for over a decade (and PWM for decades before that), I 'disagree' with all your disagreements- a high voltage series array is not an 'extra 10w for 30 mins' it is a very significant 20%-30% boost in total output generated per day, the total efficiency of modern MPPT charge controllers(and the Victron is not a modern design, having used the exact same circuitry for almost exactly a decade lol) is higher at higher voltages, with both IR losses and semiconductor switching losses increased at lower voltages offsetting the conversion losses at higher voltages
Shading can be an issue, but with most modern panels using multiple bypass diodes (the two 35w and 55w panels are a concern, many of these only have a single one- not sure as I have never heard of these brand panels before), it is less of a concern, and due to the layout of the panels, the only way to increase output any further would be fitting an individual charge controller to every single panel...

Bop said:

Victron itself states that the 100/50 requires a minimum of 5v above the battery to START... (on a 17.9v array voltage, on a 12.8v battery??? thats 5.1v, which a loaded PV array may not make until well into the morning, in some locations it may never reach it all day!!!) Worse, that 12.8v is itself a wrong value (it is commonly quoted as the nominal voltage, only a very deeply discharged LFP battery would be that low, 13v is closer to the correct value and that pushes the Victrons start voltage to get into MPPT up to 18v, which that 17.9v array all in parallel is quite likely to never get to all day...)

Click to expand...

Yes, those are the specs I quoted to you. Nonsensical. Why are you using Vmp? Voc applies. Not a single panel referenced has a Voc less than 21.6V.

Bop said:

Having measured, repaired and used MPPT charge controllers for over a decade (and PWM for decades before that), I 'disagree' with all your disagreements- a high voltage series array is not an 'extra 10w for 30 mins' it is a very significant 20%-30% boost in total output generated per day, the total efficiency of modern MPPT charge controllers(and the Victron is not a modern design, having used the exact same circuitry for almost exactly a decade lol) is higher at higher voltages, with both IR losses and semiconductor switching losses increased at lower voltages offsetting the conversion losses at higher voltages

Click to expand...

It's very possible to not understand something and draw wrong conclusions for decades. You're claiming that with nominal voltage panels corresponding to batteries, there is ZERO benefit of a MPPT vs. PWM. PWM have an inherent 20-30% penalty due to forced operation at battery voltage. Your claim is if you put those same "12V" panels on an MPPT, there will be no benefit over PWM. That's just absurd.

Thank you both for your input. I knew from the start 100% efficiency wouldn't be possible. I'll continue with the wiring, sunshine_egg outlined as that's what I had in mind and wired up yesterday on the ground. I'll mount it today and if it's really underperforming after some weeks, I'll give the parallel option a try later. It's really not hard to reconfigure later on so it might be fun just to check out some performance metrics in a real world situation like this.

STRING 1:

2X 100W in parallel, wired in series with 1 200W:

39.9 Vmp
9.8A Imp (limits 5.13A * 2 = 10.26A to 9.8A)

STRING 2:

In series with each other

37.4Vmp
2.94A

STRING 3:

In series with each other
35.8Vmp
1.96A

Parallel all three strings:

35.8Vmp
9.8A + 2.94A + 1.96 Imp = 14.7A

35.8Vmp * 14.7A = 526W vs. 580W rated

When evaluating the configuration, if battery is nearly charged, it will throttle the panel output. To truly assess PV performance, charger must be in bulk mode, and/or you need loads > PV power.

I find that mismatched panel actual production versus theoretical can have a few surprises. Partly this is because it is rare to hit rated wattage with most setups. There is also adjustments that the MPPT does when seeking the maximum power point that can be decidedly different at the total array voltage. My philosophy is if your array routinely gives you from 75-80% peak rated wattage it is doing good. If it is less than 70% than you ought to change the setup.

Given you are using the same brand of panels with same Voc with double or 1/2 the amperage rating
indicates that it is likely these are all built from the SAME cells or at least very similar so,
that series/parallel arrangement you are using is probably identical to the series parallel arrangement
already in use in the 200W panels!!. you lucked out with probably the best possible set of oddball panels
I have ever heard on this forum, Congrats

jjww said:

Given you are using the same brand of panels with same Voc with double or 1/2 the amperage rating
indicates that it is likely these are all built from the SAME cells or at least very similar so,
that series/parallel arrangement you are using is probably identical to the series parallel arrangement
already in use in the 200W panels!!. you lucked out with probably the best possible set of oddball panels
I have ever heard on this forum, Congrats

Click to expand...

I have to agree with this, particularly when factoring in the crazy power disparity.

Mattb4 said:

I find that mismatched panel actual production versus theoretical can have a few surprises. Partly this is because it is rare to hit rated wattage with most setups. There is also adjustments that the MPPT does when seeking the maximum power point that can be decidedly different at the total array voltage. My philosophy is if your array routinely gives you from 75-80% peak rated wattage it is doing good. If it is less than 70% than you ought to change the setup.

Click to expand...

@b33son

This and flat on ground means cells are likely even hotter than they might be on the roof due to zero convection. Once you've gotten your theoretical array performance for a given condition, I'd quickly check just the 200W panel and see how its performance compares to reated for a baseline.

If your frankenarray is performing at 70% of theoretical, but the single 200W is performing at 75% of theoretical, that feels like a big win.

sunshine_eggo said:

Yes, those are the specs I quoted to you. Nonsensical. Why are you using Vmp? Voc applies. Not a single panel referenced has a Voc less than 21.6V.



It's very possible to not understand something and draw wrong conclusions for decades. You're claiming that with nominal voltage panels corresponding to batteries, there is ZERO benefit of a MPPT vs. PWM. PWM have an inherent 20-30% penalty due to forced operation at battery voltage. Your claim is if you put those same "12V" panels on an MPPT, there will be no benefit over PWM. That's just absurd.

Click to expand...

LOL- nice strawmen you like knocking down- shame literally not one of your 'arguments' has anything to do with anything I actually said...
What do you think Voltage Open Circuit means???
(hint- the open circuit bit has something to do with it)
And no- I never claimed that MPPT has no inherent value over PWM- in fact that is the exact opposite... (look at that straw fly!!!)
However an MPPT will not make any more than a PWM until it gets a high enough voltage to start operating in its MPPT mode- until then, they are running in basically PWM mode... and as your array is connected and loading the panels in PWM mode- the Voc has literally nothing to do with any of this...
And (one of the few things you got right) the panels will load down to the lowest level (17.9v for the 35w panels) and the MPPT circuitry on a Victron 100/50 doesn't start operating until it hits 5v above the battery voltage- well we got a problem don't we...
Especially as the voltage curve on a panel means it won't get anywhere near it until well into the day...


These are from a different panel (I just had these handy lol)- the voltage scale would be with the knee at 17.9v, and the Voc at 21.6v, but they all exhibit pretty much the same shape voltage curves- with the knee at 17.9v, the panels voltage is well under the minimum needed to start (not run, start) the MPPT circuitry, and as I repeatedly said- it may not even get into MPPT mode at all, if it does, it will be late in the morning if it manages at all... until then it is running as a 'very expensive PWM' controller...
Where the two in series system will only have reach half that voltage for each panel before the (superior output) MPPT circuitry kicks into life (and if you had more in series, the earlier that happens in the day, which increases the daily total power generation over the low voltage MPPT or PWM systems- which is why the high voltage systems are superior...
If you had four in series (thats getting dangerously high for the 100/50, with its extremely low PVmax rating, due to the age of its design) each panel would only have to get to 1/4 of that 'around 18v' needed, a mere 4.5v approximately per panel before the MPPT circuitry starts up and you get that 30% improvement...
(mind you, the parallel array while it is sitting at only 4.5v or there abouts, can't put a single nanoamp of charge into the battery as it has to be above the battery voltage to be able to charge at all (4.5v doesn't charge a '12v nominal' battery very well for some reason lol) and yet the high voltage MPPT is already sucking every milliwatt of power it can from that array and putting it into the battery bank...)

Bop said:

What do you think Voltage Open Circuit means???

Click to expand...

What PV voltage is supplied to the MPPT before it starts?



So, BEFORE THE MPPT starts, i.e., NO operation at all, WHAT IS THE PV VOLTAGE?

Answer that one question, and you'll finally understand.

Bop said:

(hint- the open circuit bit has something to do with it)
And no- I never claimed that MPPT has no inherent value over PWM- in fact that is the exact opposite... (look at that straw fly!!!)

Click to expand...

You claimed 2S PV on MPPT will get 20-30% more than 1S PV on MPPT.
PWM performs 20-30% below MPPT.

So no difference between same panels on a PWM vs. MPPT.

Do you see now? LOTS of evidence on this site that folks running ~18Vmp panels on an MPPT operate at Vmp voltage and get power at the MPP. You're simply spreading FUD with misinformation based on ignorance of how something works.

Bop said:

However an MPPT will not make any more than a PWM until it gets a high enough voltage to start operating in its MPPT mode- until then, they are running in basically PWM mode... and as your array is connected and loading the panels in PWM mode- the Voc has literally nothing to do with any of this...
And (one of the few things you got right) the panels will load down to the lowest level (17.9v for the 35w panels) and the MPPT circuitry on a Victron 100/50 doesn't start operating until it hits 5v above the battery voltage- well we got a problem don't we...
Especially as the voltage curve on a panel means it won't get anywhere near it until well into the day...

Click to expand...

You simply just don't understand that +5V is satisfied by panel Voc. If a panel is sitting at 20Voc with battery at 14V, MPPT operation will commence and continue until PV is Battery +1V.

Given that you lack a basic understanding of this concept, there is no point in addressing anything further. Maybe you're familiar with different equipment that behaves as you describe, but that's simply not the case with Victron MPPT.

And more strawmen and more insults...
and still wrong...