Series Parallel Advice

WD56

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I'm hoping to get some advice on a series parallel setup for 12 panels.
Im thinking the best setup would be 4S3P with the 3 strings going into a combiner box with a 20 amp fuse for each. (MIDNITE SOLAR TOUCH SAFE 30A FUSE, DIN RAIL 1000VDC)
My thinking is that I would want high voltage hence the 4S getting the volts up to 200 VOC but under the max for the mppt (250)

Does this feel right ? is there a better setup? my panels are ground mount about 220 feet from the MPPT
Im wondering if I need OCPD for each string ? or does the fuse in the combiner box suffice this need?

Any help is hugely appreciated.

Equipment:
MPPT:
Victron Mppt 250 - 100
Solar:
12 x BluSun 460 Bi Factials from Signature Solar

Performance at STC
Pmax/W 460
Vmpp/V 42.6
Impp/A 10.86
Voc/V 50.8
Isc/A 11.50

Maximum series Fuse 25A
Maximum System Voltage 1500 V/DC (IEC)
 

sunshine_eggo

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My thinking is that I would want high voltage hence the 4S getting the volts up to 200 VOC but under the max for the mppt (250)
Does this feel right ?

Yep

is there a better setup?

Not without higher PV voltage and a more expensive MPPT.

my panels are ground mount about 220 feet from the MPPT

Ouch

Im wondering if I need OCPD for each string ?

Yes, for 3P or more, each string needs OCP in accordance with fusing requirement on panel label.

or does the fuse in the combiner box suffice this need?

If the combiner box provides a fuse/breaker for each string, then you're good. If there's only one at the output, that's bad.

Maximum series Fuse 25A
Maximum System Voltage 1500 V/DC (IEC)

Each string should have a fuse, 25A or less. 15-20A should be fine for those panels.
 

Horsefly

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my panels are ground mount about 220 feet from the MPPT
My cabin ground mount is just over 200 feet from the MPPT. In the old days the rule of thumb was to try and keep the round trip loss on the wire to be 3% or less (based on Vmp / Imp). However, the price per watt of panels is way cheaper now (maybe going up?), so you need to look at the trade between increasing # of panels vs the cost of big wire. That is, it may make more sense to add another parallel string of panels and accept that the loss may be over 3%.
 

12VoltInstalls

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may make more sense to add another parallel string of panels and accept that the loss may be over 3%.
Although higher volt series panels with the right SCC may wind up being <3% which is why more panels is a good idea usually 😀
 

MichaelK

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What are the winter lows in your area like? A solar string with a Voc of ~200V will exceed 250V at approximately -40degrees. Not a big problem in Arizona, but if you are in Montana, you need to be more cautious.

BTW, my own mounts are as far as 130' from the controller, and running at 120VDC, I'm not measuring any significant voltage drop with 10 gauge cable. So 3S4P might also work. Have you put it through a drop calculator yet?
1649783845173.png
 

newbostonconst

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I have a 4s4p array and started with the midnight 250 and produced 20kwh on a sunny day, did some research and switched to the 200 version and now produce 25kwh on a sunny day. My voltage never goes above 140 volts even on minus 10 degree mornings.

Point I am making is the higher voltage SCC's aren't as efficient. I wanted to get the voltage up to save on wire cost because the array is 250 feet away. I ran 12 awg. with the midnight breaker box. I feed the 4 strings into breakers and combine them with the supplied buss bar and then flipped the 5 breaker upside down in the box to get the current to flow the right direction through the breaker to feed out to the 12 awg wire to the house SCC.
 
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MichaelK

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Point I am making is the higher voltage SCC's are as efficient. I wanted to get the voltage up to save on wire cost because the array is 250 feet away. I ran 12 awg. with the midnight breaker box. I feed the 4 strings into breakers and combine them with the supplied buss bar and then flipped the 5 breaker upside down in the box to get the current to flow the right direction through the breaker to feed out to the 12 awg wire to the house SCC.
I think that statement is not actually true. I believe what you are really talking about is the amp limit of Midnight's controllers. I have Midnight also, so I am very familar with their literature. If you look at this graph pulled from the Classic manual, it shows how at higher voltage, the unit is actually slightly less efficient. The same effect holds true for the 150V and 200V model(mine)
1649871578549.png
I think what you are actually seeing is more related to the amp limit of each individual unit. When you switched from the 250 to the 200, your raised your amp limit from 55A to 65A, so more power is able to pass through the unit. BTW, I'm seeing the same thing, in that I can make about 25kWh of power per day, passing it all through the Classic200.
1649871695978.png
 

newbostonconst

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I think that statement is not actually true. I believe what you are really talking about is the amp limit of Midnight's controllers. I have Midnight also, so I am very familar with their literature. If you look at this graph pulled from the Classic manual, it shows how at higher voltage, the unit is actually slightly less efficient. The same effect holds true for the 150V and 200V model(mine)
View attachment 91094
I think what you are actually seeing is more related to the amp limit of each individual unit. When you switched from the 250 to the 200, your raised your amp limit from 55A to 65A, so more power is able to pass through the unit. BTW, I'm seeing the same thing, in that I can make about 25kWh of power per day, passing it all through the Classic200.
View attachment 91095
You are correct.... I stated they are as efficient and it got typed out wrong, should have said aren't(I fixed it)..... The higher voltage SCC aren't as efficient....

Thanks
 

flatwerx

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I've been reading a ton on parallel vs series and I'm still unsure what I should do. I'm super new to solar.
Here's my current setup in my off-road teardrop that I live in full-time (no house or apartment to go home to) (everything is Renogy):
2 100Ah lithium batteries
20Amp solar controller/charger
60 DC-DC charger between vehicle and trailer
Lithium shore power inverter
1 100 watt portable briefcase solar panel (Voc): 24.3V) (Maximum Series Fuse Rating: 20A) (cable is 10' long)
.

What I'd like to add:
1 rigid 200 watt Renogy panel to the roof rack of the trailer (Voc: 27V) (Maximum Series Fuse Rating: 15A) (cable would be 10' long)
.

My question(s): do I run these in parallel or series?
Its a 12V system and I'm unsure if providing more voltage is good/bad or more amps.
Thanks!
Adam
 

sunshine_eggo

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100W panel likely has a Vmp around 20.6V. 100W/20.6V = 4.85A
200W panel likely has a Vmp around 23.0V. 200W/23.0V = 8.70A

If you put them in series, you would force the 200W panel to run at 4.85A, so you'd cripple it to 4.85A * 23V = 112W

If you put them in parallel, they would operate somewhere between 20.6 and 23V (closer to 20.6) and operate at their respective currents, so the 200W panel might take a 10% hit.
 

MichaelK

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To give you an appropriate answer, we really need all the specifications of both your panels, and the controller, not just the Voc. Also supply us with the Vmp, Isc, and Imp of the panels, and the make and model of the controller. We need to know whether it's MPPT, or PMW, and whether it's a "real" MPPT or a fake copycat product. A picture of the controller would be great
 

Horsefly

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If you put them in parallel, they would operate somewhere between 20.6 and 23V (closer to 20.6) and operate at their respective currents, so the 200W panel might take a 10% hit.
Hey @sunshine_eggo - I would normally defer to your expertise, but this goes counter to what I've always believed (and think I've read a few times): That series panels will be limited to the Imp of the lowest current panel, and that parallel panels will be limited to the lowest Vmp. I.e., I didn't think you could get the voltage in this case above 20.6V by putting the panels in parallel. Is that wrong?

I realize it isn't far off from your "closer to 20.6", but I'm curious.
 

flatwerx

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Thanks guys!
Controller: Renogy Rover Elite 20A MPPT Solar Charge Controller
100 Watt briefcase: Optimum Operating Voltage (Vmp): 20.3V, Short-Circuit Current (Isc): 2 x 2.73A, Optimum Operating Current (Imp): 2x2.47A
.

200 Watt 12 Volt Monocrystalline Solar Panel: Optimum Operating Voltage (Vmp): 22.6 V, Short Circuit Current (Isc): 9.66A, Optimum Operating Current (Imp): 8.85 A
 

sunshine_eggo

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Hey @sunshine_eggo - I would normally defer to your expertise, but this goes counter to what I've always believed (and think I've read a few times): That series panels will be limited to the Imp of the lowest current panel, and that parallel panels will be limited to the lowest Vmp. I.e., I didn't think you could get the voltage in this case above 20.6V by putting the panels in parallel. Is that wrong?

I realize it isn't far off from your "closer to 20.6", but I'm curious.

I know. I've seen the videos and the webpage. It's a shortcut to simplify the issue and create an analogy to the series rule.

With two different Vmp panels in parallel, you move the MPP. With a more powerful panel at a higher Vmp it may perform a little better a little above the Vmp of the lower panel. The 100W panel will still put out current at a decreasing rate until Voc is hit, so the MPP of the combined array may be a little above the lower Vmp panel, particularly with a larger panel at a higher power.

Imagine 10X of the 200W panels in parallel with the 100W panel. Do you think the 2000W array would take a full 200W hit to operate at the lower Vmp? The MPPT would find it at somewhere closer to the 200W Vmp in this case. This will happen as long as the lower Voc is above the higher Vmp - substantial overlap between the Vmp-Voc range.

Refer to this figure to visualize how a small increase in V doesn't really impact the power a large degree:

1660146360951.png

Raising the combined Vmp above the lower panel by a small amount won't have a large impact, but it may benefit the larger panel by more than is lost, so the MPP will be between the two Vmps. Due to the variance in slope on either side of the peak power point, there is a tendency to be closer to the lower Vmp for comparable power.
 

Horsefly

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I know. I've seen the videos and the webpage. It's a shortcut to simplify the issue and create an analogy to the series rule.

With two different Vmp panels in parallel, you move the MPP. With a more powerful panel at a higher Vmp it may perform a little better a little above the Vmp of the lower panel. The 100W panel will still put out current at a decreasing rate until Voc is hit, so the MPP of the combined array may be a little above the lower Vmp panel, particularly with a larger panel at a higher power.

Imagine 10X of the 200W panels in parallel with the 100W panel. Do you think the 2000W array would take a full 200W hit to operate at the lower Vmp? The MPPT would find it at somewhere closer to the 200W Vmp in this case. This will happen as long as the lower Voc is above the higher Vmp - substantial overlap between the Vmp-Voc range.

Refer to this figure to visualize how a small increase in V doesn't really impact the power a large degree:

View attachment 106271

Raising the combined Vmp above the lower panel by a small amount won't have a large impact, but it may benefit the larger panel by more than is lost, so the MPP will be between the two Vmps. Due to the variance in slope on either side of the peak power point, there is a tendency to be closer to the lower Vmp for comparable power.
Wow, very interesting thought. Thanks for giving the full explanation.

I'd love to see if anyone has tried to verify one way or the other. Your example of 10x of the higher voltage panel with one of the lower voltage panels is somewhat compelling. It just doesn't match with what I would expect.
 
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