Redesigning panels from 12V to 24V layout- Could someone check my total VOC Please?

[Echo]

Hi, I am upgrading from a 12V system to 24V (replacing 12V-3500W inverter to 24V-4000W LFP inverter and connecting two 12V - 300AH batteries in series with a Victron battery balancer - having to remove the 3rd 12V- 300AH battery) and will redesign my existing panels for my 80 AMP/200V 12/24/36/48v Controller.

My panel redesign will be 3 strings of series/parallel with the slightly off string being #3 (the volts - matching Lowest Common Denominator, 36.3V), then parallel those 3 strings together (36V x 48.73A = 1754.28 Watts).

Big question - will my total VOC (bottom right corner as a question mark) also be Lowest Common Denominator (86.4 VOC) or am I wrong on the Voltage and its actually Highest Common Denominator (87.8 VOC)?

Panel fuses, etc... will be applied, just not noted.

Picture attached.

Thanks in advance!

 

[MichaelK]

You are making fundamental mistakes here. You do NOT have three strings, you have six. Secondly, is this the inverter you are talking about? This inverter does NOT have a solar MPPT charger, the charger mentioned is for AC generator input charging. You will need a separate MPPT solar charge controller between the batteries and the solar panels.


So, let's start out with some re-design here. I'd suggest forgetting about the wiring scheme you outlined above. Overly complicated, and too low a voltage. With a good high-voltage MPPT controller, you need only two strings, wiring the six larger panels into one series string putting out 10A at 110Vmp (Voc 131), and string two putting out 5.5A at 108Vmp (Voc 129V).

What are your winter lows like? Choices for controllers include 150V, 200V, 250V, and 300V models, with the price going up as the voltage limit goes up. Let's look at an economy brand, Epever. Their Tracer 8415 and 8420 models will work for you, the 8415 OK for more Southern climates, but the 8420 better for up North. With a Voc of 131, that will bump up past 150V somewhere around zero degrees F, though with the 8420, you can surpass -40F without going over-voltage. I think the Tracer 8420AN is somewhere in the 350$ range on Amazon/Ebay right now.

With two strings at 10A at 110V and 5.5A at 108V, you'll potentially make as much as 1100W + 595W = 1695W. Charging at 25V, you are likely to never exceed 1695W/25V = 67.8A, so an 80A controller will work for you. Most likely your real-world amps is really not likely to ever exceed 58-59A, so maybe a slightly lower capacity controller, say the 6420AN would be OK. But, I think a bit of over capacity is worth the few extra dollars.

A couple of important points. In series, volts add while amps stay the same. In parallel amps add while voltage stays the same. In the example I've given you below, the 10-11A panels are kept separate from the 5.5A panels. You never want to mix the 10-11A panels in the same series string as the 5.5A, because all the panels amps will be dragged down to what the lowest one can transmit.

But, in my example, you are mixing 10A panels with 11A panels, which means you'll be losing 1A wiring them that way. But, by doubling/tripling the voltage, you lose less power via copper wire resistance.

If you really want to spend the time to calculate things down to the single watt range, use a voltage drop calculator like this one to decide which the very best series string combinations.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[Echo]

You are making fundamental mistakes here. You do NOT have three strings, you have six. Secondly, is this the inverter you are talking about? This inverter does NOT have a solar MPPT charger, the charger mentioned is for AC generator input charging. You will need a separate MPPT solar charge controller between the batteries and the solar panels.
View attachment 225711

So, let's start out with some re-design here. I'd suggest forgetting about the wiring scheme you outlined above. Overly complicated, and too low a voltage. With a good high-voltage MPPT controller, you need only two strings, wiring the six larger panels into one series string putting out 10A at 110Vmp (Voc 131), and string two putting out 5.5A at 108Vmp (Voc 129V).

What are your winter lows like? Choices for controllers include 150V, 200V, 250V, and 300V models, with the price going up as the voltage limit goes up. Let's look at an economy brand, Epever. Their Tracer 8415 and 8420 models will work for you, the 8415 OK for more Southern climates, but the 8420 better for up North. With a Voc of 131, that will bump up past 150V somewhere around zero degrees F, though with the 8420, you can surpass -40F without going over-voltage. I think the Tracer 8420AN is somewhere in the 350$ range on Amazon/Ebay right now.

With two strings at 10A at 110V and 5.5A at 108V, you'll potentially make as much as 1100W + 595W = 1695W. Charging at 25V, you are likely to never exceed 1695W/25V = 67.8A, so an 80A controller will work for you. Most likely your real-world amps is really not likely to ever exceed 58-59A, so maybe a slightly lower capacity controller, say the 6420AN would be OK. But, I think a bit of over capacity is worth the few extra dollars.

A couple of important points. In series, volts add while amps stay the same. In parallel amps add while voltage stays the same. In the example I've given you below, the 10-11A panels are kept separate from the 5.5A panels. You never want to mix the 10-11A panels in the same series string as the 5.5A, because all the panels amps will be dragged down to what the lowest one can transmit.

But, in my example, you are mixing 10A panels with 11A panels, which means you'll be losing 1A wiring them that way. But, by doubling/tripling the voltage, you lose less power via copper wire resistance.

If you really want to spend the time to calculate things down to the single watt range, use a voltage drop calculator like this one to decide which the very best series string combinations.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

6 Strings? Thank you.

I'll look into the design again, it was my first attempt. I wasn't sure where to keep the voltage range, coming from a 12V system.

I do have the 8420, its what I will reuse but I did buy the inverter you mentioned, the 120V version. I like to keep the Inverter and MPPT separate.

Winters avg about 30F to -10F at the lowest.

I'm limited in panel locations and did think about trying to keep the larger panels together, so thanks for the second pair of eyes and appreciate the advice.

 

[Echo]

You are making fundamental mistakes here. You do NOT have three strings, you have six. Secondly, is this the inverter you are talking about? This inverter does NOT have a solar MPPT charger, the charger mentioned is for AC generator input charging. You will need a separate MPPT solar charge controller between the batteries and the solar panels.
View attachment 225711

So, let's start out with some re-design here. I'd suggest forgetting about the wiring scheme you outlined above. Overly complicated, and too low a voltage. With a good high-voltage MPPT controller, you need only two strings, wiring the six larger panels into one series string putting out 10A at 110Vmp (Voc 131), and string two putting out 5.5A at 108Vmp (Voc 129V).

What are your winter lows like? Choices for controllers include 150V, 200V, 250V, and 300V models, with the price going up as the voltage limit goes up. Let's look at an economy brand, Epever. Their Tracer 8415 and 8420 models will work for you, the 8415 OK for more Southern climates, but the 8420 better for up North. With a Voc of 131, that will bump up past 150V somewhere around zero degrees F, though with the 8420, you can surpass -40F without going over-voltage. I think the Tracer 8420AN is somewhere in the 350$ range on Amazon/Ebay right now.

With two strings at 10A at 110V and 5.5A at 108V, you'll potentially make as much as 1100W + 595W = 1695W. Charging at 25V, you are likely to never exceed 1695W/25V = 67.8A, so an 80A controller will work for you. Most likely your real-world amps is really not likely to ever exceed 58-59A, so maybe a slightly lower capacity controller, say the 6420AN would be OK. But, I think a bit of over capacity is worth the few extra dollars.

A couple of important points. In series, volts add while amps stay the same. In parallel amps add while voltage stays the same. In the example I've given you below, the 10-11A panels are kept separate from the 5.5A panels. You never want to mix the 10-11A panels in the same series string as the 5.5A, because all the panels amps will be dragged down to what the lowest one can transmit.

But, in my example, you are mixing 10A panels with 11A panels, which means you'll be losing 1A wiring them that way. But, by doubling/tripling the voltage, you lose less power via copper wire resistance.

If you really want to spend the time to calculate things down to the single watt range, use a voltage drop calculator like this one to decide which the very best series string combinations.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

Hi MichaelK,
as I started to design 2 strings in series, I realized I get a lot of shading and then remembered why I was trying to avoid it.

I assume the Series/Parallel design in a couple/few strings would bring only one string in shade down and allow any other strings not in shade to continue?

Thanks in advance!