Which way to run solar panels…series or parallel

[DBK]

I have 8 panels

200 watts
27 VOC
9 amp (10-12 I would guess)

Should I run;

Series, 8x27=216 volts and 10-12 amps for 1600 watts
Or
Parallel, 8x10=12 volts and 80 amps for 1600 watts

I am still choosing my charge controllers…so I am looking at either 2 smaller ones or a one larger one

Am I thinking about this correct?

Thanks in advanced

 

[BentleyJ]

Series is better because it reduces the amperage and the wires can be smaller. There are many choices for charge controllers, if you can get one that will handle all 8 panels in series that is the simplest. Alternatively many 150V input charge controllers are available so perhaps 2 series strings of 4 panels would also work. Remember: Higher DC voltages are dangerous and calculate your VOC at the coldest temperatures you expect for your area to make sure the maximum voltage will never exceed the rating of the CC you select.

 

[sunshine_eggo]

There is no meaningful answer.

Your system voltage and choice of charge controller will place restrictions on how you wire your panels.

Your choices are currently:

8P
8S
2S4P
4S2P

There is no evidence to indicate that any of the above are better than the other for your application.

 

[Samsonite801]

What battery voltage are you running?

I know on my Victron charge controllers, they cap the watts at 1450w when running on a 12v bank, so in my case if I had wanted the 3200w that I desired, I had to buy two charge controllers...

 

[GLC]

There is no meaningful answer.

Your system voltage and choice of charge controller will place restrictions on how you wire your panels.

Your choices are currently:

8P
8S
2S4P
4S2P

There is no evidence to indicate that any of the above are better than the other for your application.

This

 

[chriscappuccio]

Pretty sure the VOC is the wrong voltage to calculate against for watts/amps under load. My 24v panels have a VOC over 40v but under load are working some 8-10v under the VOC value. I can't remember the exact numbers.

They even have a label with both values, for these calculations. So with a loaded voltage below your VOC, your amps will be higher than 80 amps, and if you have any kind of wire distance, you will be able to use smaller wire by having some amount of panels in series.

 

[chriscappuccio]

It seems like a shaded panel will also provide more resistance, and that affects all panels in the series, So if you have uncontrollable shading, you want more panels in parallel and you should go for the bigger wire. This is the main argument for smaller groups in series, or putting them all in parallel.

 

[iamrich]

Pretty sure the VOC is the wrong voltage to calculate against for watts/amps under load. My 24v panels have a VOC over 40v but under load are working some 8-10v under the VOC value. I can't remember the exact numbers.

You definitely want to use VOC when choosing your inverter, and even then, you want to give yourself a little wiggle room for temperature. If you use the lower number and series right up to the max value of your inverter, there will be a very good chance you will release the magic smoke...

 

[chriscappuccio]

Even the solar charge controller manuals say to use VOC in calculations, I'm not disputing that. They need to, the way MPPT functions, it has to shut off the load for a brief period to calculate where the panels are at. So, it must be exposed to VOC. Absolutely, use VOC for calculating the max voltage that should go into your MPPT.

What I'm saying is, just like you must use the more conservative value for sizing your MPPT with the solar series voltage, you must also use the more conservative number when sizing your wire. The conservative number for your solar load isn't the high VOC number, it's the lower number which results in a higher on-wire amperage. The "Open Circuit" number represents no current, but high voltage to your MPPT. The lower voltage number represents current, so your wire must be big enough to support it.

 

[sunshine_eggo]

It seems like a shaded panel will also provide more resistance, and that affects all panels in the series, So if you have uncontrollable shading, you want more panels in parallel and you should go for the bigger wire. This is the main argument for smaller groups in series, or putting them all in parallel.

Nope. If shade induces underperformance (less current) from one panel, that portion of the panel is bypassed via the internal bypass diode. This allows the other panels to remain fully functional.

Even the solar charge controller manuals say to use VOC in calculations, I'm not disputing that. They need to, the way MPPT functions, it has to shut off the load for a brief period to calculate where the panels are at. So, it must be exposed to VOC. Absolutely, use VOC for calculating the max voltage that should go into your MPPT.

What I'm saying is, just like you must use the more conservative value for sizing your MPPT with the solar series voltage, you must also use the more conservative number when sizing your wire. The conservative number for your solar load isn't the high VOC number, it's the lower number which results in a higher on-wire amperage. The "Open Circuit" number represents no current, but high voltage to your MPPT. The lower voltage number represents current, so your wire must be big enough to support it.

Isc and Vmp for wiring sizing and voltage drop calucations.

 

[DBK]

What battery voltage are you running?

I know on my Victron charge controllers, they cap the watts at 1450w when running on a 12v bank, so in my case if I had wanted the 3200w that I desired, I had to buy two charge controllers...

My bank is 12V, the manufacturer limit

 

[AntronX]

4 x (2S1P + 30A MPPT). Ideally you want all panels in parallel but PV wire voltage drop will be large unless you keep it < 5 feet. Is there any shading ?

 

[DBK]

4 x (2S1P + 30A MPPT). Ideally you want all panels in parallel but PV wire voltage drop will be large unless you keep it < 5 feet. Is there any shading ?

No shading, wide open

 

[DBK]

No shading, wide open

4 x (2S1P + 30A MPPT). Ideally you want all panels in parallel but PV wire voltage drop will be large unless you keep it < 5 feet. Is there any shading ?

Do I need a combiner box for the panels that way? Makes sense…didn’t know I could do it that way

2S, 54 Volts 12 amps 200 watts

X4 in parallel,

8 panels, (4 groups of 2) 54 Volts 48 amps 1600 watts

 

[AntronX]

Do I need a combiner box for the panels that way? Makes sense…didn’t know I could do it that way

Just put 15A fuse in series with each panel before combining point. What is the PV wire length to MPPT ?

 

[DBK]

Just put 15A fuse in series with each panel before combining point. What is the PV wire length to MPPT ?

Is my above post correct? In running 4 groups of two?

 

[AntronX]

Is my above post correct? In running 4 groups of two?

2s1p at 22.6v x 8.85a = 45.2v x 8.85a = 400w
400w * 0.97 = 388w (after MPPT loss)
388w / 13.4v = 28.95a (near limit for 30a rated MPPT)

with 60A MPPT you can do 4 panels in 2s2p config or 45.2v x 17.7a = 800w

 

[DBK]

2s1p at 22.6v x 8.85a = 45.2v x 8.85a = 400w
400w * 0.97 = 388w (after MPPT loss)
388w / 13.4v = 28.95a (near limit for 30a rated MPPT)

with 60A MPPT you can do 4 panels in 2s2p config or 45.2v x 17.7a = 800w

Please bare with me as I’m a newbie…

2s2p mean, 2 panels in series 2 in parallel….as in 2 panels in series and 2 panels in series that are then paralleled? 4 panels in total being run as 2 in parallel?

 

[AntronX]

Yes. If you go with 2x 60A charge controllers with 2s2p panel config on each then you do not need fuses on panels. You only need them if you paralleling 3 or more panels or 3 series strings of panels.

 

[DBK]

How would that wiring look like?

Is there a video you could recommend? Or a drawing?