Looking for Best Panel Array Configuration...

[tripseven]

I finally got most components delivered for my 24v Sinopoly LifePO4 200ah. Pretty much just need the wiring now.

I'm using a Victron SmartSolar Charge Controller (150V 70A Tr).

Can anyone smarter than me, which would be most of you, tell me the best configuration for panel array consisting of 12 HQST 100 watt 12v polycrystalline panels with MC4 connectors? I may even increase it to 16-20 panels if necessary.

THx in advance!

 

[kernel]

You might be able to have 6 panels in series. Depends on the site, weather and how you need to mount.

 

[Forbisher]

I'm using a Victron SmartSolar Charge Controller (150V 70A Tr).
, tell me the best configuration for panel array consisting of
12 HQST 100 watt 12v polycrystalline panels with MC4 connectors?
I may even increase it to 16-20 panels if necessary.

HQST 100 watt 12v panels have Open-Circuit Voltage (Voc): 21.4V

4 panels in a Series string at 21.4V = 85.6 volts so safely under 150V 3 strings of 4 panels = 12

5 panels in a Series string at 21.4V = 107 volts so safely under 150V but does not work with 12 panels

6 panels in a Series string at 21.4V = 128 volts which may be over 150V in cold weather. 2 strings of 6 panels = 12

Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.2V	Open-Circuit Voltage (Voc): 21.4V
Optimum Operating Current (Imp): 5.50A	Short-Circuit Current (Isc): 5.70A

 

[tripseven]

You might be able to have 6 panels in series. Depends on the site, weather and how you need to mount.

This will be mostly used in the PNW. Mount would be similar to your avatar yet in a separate array will mount on top of an RV.

 

[tripseven]

HQST 100 watt 12v panels have Open-Circuit Voltage (Voc): 21.4V

4 panels in a Series string at 21.4V = 85.6 volts so safely under 150V 3 strings of 4 panels = 12

5 panels in a Series string at 21.4V = 107 volts so safely under 150V but does not work with 12 panels

6 panels in a Series string at 21.4V = 128 volts which may be over 150V in cold weather. 2 strings of 6 panels = 12

Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.2V	Open-Circuit Voltage (Voc): 21.4V
Optimum Operating Current (Imp): 5.50A	Short-Circuit Current (Isc): 5.70A

Thx for that easy to understand reply!

 

[tripseven]

6 panels in a Series string at 21.4V = 128 volts which may be over 150V in cold weather. 2 strings of 6 panels = 12

Wait...was that meant to be hot weather?

 

[Forbisher]

Wait...was that meant to be hot weather?

Panels produce less power as they get hotter than 25 C? 77 F? rated at STC Standard Test Conditions.
Under really cold conditions they make more power. 1.25 x 128 volts would be 160 Volts.

Victron SmartSolar MPPT 150/70 Wow $586
Max PV open circuit voltage: 150V absolute maximum coldest conditions, 145V start-up and operating at maximum --
Peak Efficiency: 98%

 

[tripseven]

Panels produce less power as they get hotter than 25 C? 77 F? rated at STC Standard Test Conditions.
Under really cold conditions they make more power. 1.25 x 128 volts would be 160 Volts.

Victron SmartSolar MPPT 150/70 Wow $586
Max PV open circuit voltage: 150V absolute maximum coldest conditions, 145V start-up and operating at maximum --
Peak Efficiency: 98%

Oh man... I have a lot more to learn before plugging in ugh!!!

HELP...lololol

 

[kernel]

Victron likley has a string calculator. Delends on where you are or go. I use -55°F in the calculators for systems in the north here. Usually limits us to 120ish volts open circuit. (150V)

Just run the numbers, you might be surprised.

 

[Forbisher]

I finally got most components delivered for my 24v Sinopoly LifePO4 200ah.

I'm using a Victron SmartSolar Charge Controller (150V 70A Tr).
tell me the best configuration for panel array consisting of 12 HQST 100 watt 12v panels
I may even increase it to 16-20 panels if necessary.

The Smartsolar 150/70 is a great choice for controlling up to
1000 watts of solar panels at 12V,
2000 watts at 24V, or
48V at 4000 watts.
With maximum open circuit voltage of 150 volts. It automatically selects between 12, 24, and 48 volts on the output (software tool needed to select 36V). Should the PV input exceed the rating, the controller will simply limit the the throughput to the rated level.

 

[tictag]

Victron likley has a string calculator.

It's here.


Some considerations:

1. A 1,200W array would generate around 45-50A into a 24V(nominal) battery system so the 150|70 is a bit overkill - the 150|45 would do you. But if you wanted to upgrade your PV array you could connect up to 2,000W with that SCC.
2. So long as partial shading of your array isn't an issue*, the most optimal configuration would be to connect as many panels as possible up in a series string then connect multiples of that in parallel. For example, 6 panels x 21.4V = 128.4V, that's OK, but 7 x 21.4V = 149.8V (BUST! In low temperatures).
3. Most polycrystaline PV panels have a Voc temperature coefficient of around -0.3%/℃ from 25℃, so if your 25℃ Voc was 21.4V, your 0℃ Voc would be 7.5% higher i.e. panel Voc from: 21.4V to: 23.0V and array Voc (6S2P) from: 128.4V to: 138.0V, still well within your SCC's specs.
4. So you have choices:

Array Configuration	# Panels	Array Voc	Array Isc	Array Pmax	Comments
5S3P	15	107	17.1	1,500W
5S4P	20	107	22.8	2,000W
6S2P	12	128.4	11.4	1,200W
6S3P	18	128.4	17.1	1,800W
6S4P	24	128.4	22.8	2,400W	Would need the 150|85
7S2P	14	149.8	11.4	1,400W	Would need >150V SCC
7S3P	21	149.8	17.1	2,100W	Would need >150V SCC

6S2P seems like a good choice to me, but all the others (without comments) would work with your Blue/Smart Solar 150|70 if you wanted to upgrade your array.

*Note: If partial shading is an issue, increase parallel strings e.g. 4S3P or 3S4P, or even 2S6P if it's really bad. These configurations would be sub-optimal.

Edit: Clarified panel versus array Voc under temperature change.

 

[tripseven]

Thanks for all the replies...this is a great forum!

Got a better handle on how these panels hook up now so as not to fry my SCC. Decided to just go ahead and max this setup out and do a 5S4P at 2000w since I already have this inverter.

Do I use 10 awg wire for the 1 to 4 branch connector and main run to SCC?

 

[tictag]

We try our best

Cable choice, especially for PV arrays, is very sensitive to the distance the array is from the SCC. In general, you want to avoid dropping more than 3% of the supply voltage across the run. There are loads of 'voltage drop' calculators out there but I prefer a 'first principles' approach i.e. V = IR, V(drop) = Isc x R(cable), where R(cable) can be looked up somewhere like here. To each their own.

For example, if your array cable run was say 20', that's 40' there and back and for you:

• Array Vmp = 91V (18.2V x 5 panels = 91V)
• Array Isc = 22.8A (5.7A x 4 strings = 22.8A) + 25%* = 28.5A

Cable Size	V(drop) value / %	Power(loss)	Cost
14AWG	2.9V / 3.1%	81W	$72
12AWG	1.8V / 2.0%	64W	$92
10AWG	1.2V / 1.3%	33W	$132
8AWG	0.7V / 0.7%	21W	$159

* recommended at least +25%, check NEC for further information

Calculations:
V(drop) = Isc x R(cable)
P(loss) = Isc² x R(cable)
Cost = 40' per here

So I'd be thinking 14AWG loses too much power and 8AWG is too expensive and likely too heavy. Both 12AWG and 10AWG work ... 12AWG is cheaper but would I want to lose 64W that's almost a full panel just lost to heat. I'd stump up the cash and go with 10AWG.

 

[tripseven]

Cable Size	V(drop) value / %	Power(loss)	Cost
14AWG	2.9V / 3.1%	81W	$72
12AWG	1.8V / 2.0%	64W	$92
10AWG	1.2V / 1.3%	33W	$132
8AWG	0.7V / 0.7%	21W	$159

Thanks again for the help! The charts you use are very nice. Are they part of a software program?

 

[tictag]

These tables, you mean? If so, no, inserting a table is just one of the options in the post editor. It's a bit clunky but works.

 

[tripseven]

OK, so I'm down to wiring my 2000w scenario. A DC +40' run from panels is not looking good as it seems due to lost power at this length. Would it be best to station batts and inverter closer to the panels and run AC from the inverter to power source of about 30' from source? For clarity...is it best to run long lengths across AC in this fashion rather than DC?

 

[MisterSandals]

For clarity...is it best to run long lengths across AC in this fashion rather than DC?

The higher the voltage and lower the amps, the better. Whether you can do that better/easier/cheaper as AC or DC are probably the major factors you should consider.