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Do volts matter?

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Ok I have something strange going on, I 2 arrays of 305w (VoC 39.9 each) panels. Both arrays are at the same angles and facing the same direction. Somehow array 2 is pulling in the same amount of watts as array 1 how is that? Could it be that having more panels in series at higher volts make the panels more efficient?

Array 1 - 3 strings of 3 (119.7v each string)
Array 2 - 2 strings of 4 (159.6v each string)

Any answer to this would help thank you.
 
Your description is confusing but I’m guessing bar what you meant.

Yes volts matter.

Because they are not balanced one is pulling down the other is a wildhat guess.

If the two arrays aren’t balanced use two SCCs
 
If all panels are identical, then it does not matter much how you mix them; they should produce the same.

In your arrays you have one with 9 panels and one with 8; so Array 1 with nine panels should produce more. You mention that both arrays produce the same and ask for the rootcause. We miss information.

You provide array voltages; are these Open Voltages?
Have you measured voltage during operation? Should be lower than the VOC; with MPPT controller actually around the optimal power point.
Which is the max. power of your controllers/inverters? Could load be limiting your array output?
Made sure no shadows or infrastructure that could limit light exposure? (Even indirect)
Which outputs are you having from the arrays and how similar they are? You observe this parity phenomenon always?
 
...array 2 [ 2 strings of 4=8 panels] ... same amount of watts as array 1 [3 strings of 3 = 9 panels] how is that [possible]? ... same angles ...

  • Trick question! Your post is timecoded as 5:19 AM, so both arrays are outputting zero because the sun isn't up ; -)
The fault probably lies with Array 1 for two reasons:
  1. Problems create less power not more,
  2. That they're equal means you're missing the entire output of exactly one panel.
That you're off exactly one panel's worth of power points to a panel issue.
I'd say check the 3 connectors/volts/amps of the end panels in array one, or signs of shading/dirt on one of those panels.

Use array 2 to calculate the insolation, that is insolation = total watts array 2 / 8 / 305, for example if array 2 generates 9800 Wh in a day, then then insolation is 9800/8/305 = 4, so array 1 should output 4 x 9 x 305 = 11,000 Wh. Keep playing with array 1 until you see that plus or minus a few percent.

Do volts matter?
There can be an efficiency bonus to higher voltages, but usually that would be fairly small.
Also, MPPTs do have a minimum starting voltage so array 1 starts producing power after array 2 and stops before array 2, but that's probably minimal too.
 
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I'd say check the 3 connectors to the end panels in array one, or signs of shading/dirt on one of those panels.
Seems to me that based on the number of panels, array configuration, and actual output wattage you could mathematically narrow in on which panels to check or even get an idea as to whether it was a connection issue, shading or dirt issue. At least starting points to measure amps/volts.

Any of you string inverter gurus know of a program that does that?
 
If the array is very far from the SCC, there can be more loss in the lower voltage array?

Again, need more info
 
1. All the panels are the same and I got them at the same time.
2. They are on 2 MPPT 100a 200v controllers, so the problem must be with the panels or the MPPTs.
3. All the panels are in the same area some are a little closer than the others but not by much.
4. Yes that is the open circuit voltage

So it sounds like the proems is with my array of 9 panels or the Mppt they are connected to is that about right?
 
Can you give us the model number of the mppt controllers? Perhaps they have limited charging amperage and you have reached the charging limit on both of them, hence the same max output to the batteries.
 
Can you give us the model number of the mppt controllers? Perhaps they have limited charging amperage and you have reached the charging limit on both of them, hence the same max output to the batteries.
That could be possible If you have a MPPT inverter instead of a controller. What I see is that Inverters are often rated on output and have a lower PV input limit. Then I also see that Controllers are more often sized to input and output or else it is clearly indicated on the model name. 100A is far above the max. current of your arrays and should be ok.

Check the voltage of the arrays when connected to the MPPT and provide us the numbers. You gave us VOC of the arrays showing us that all the panels seem to be working well; but we don't know how they output their power.

If the current of both arrays is the same or the voltage of array 1 is closer/higher than the voltage of array 2, then you know that array's 1 current is being limited by the controller.

  • Trick question! Your post is timecoded as 5:19 AM, so both arrays are outputting zero because the sun isn't up ; -)
The fault probably lies with Array 1 for two reasons:
  1. Problems create less power not more,
  2. That they're equal means you're missing the entire output of exactly one panel.
That you're off exactly one panel's worth of power points to a panel issue.
I'd say check the 3 connectors/volts/amps of the end panels in array one, or signs of shading/dirt on one of those panels.

Use array 2 to calculate the insolation, that is insolation = total watts array 2 / 8 / 305, for example if array 2 generates 9800 Wh in a day, then then insolation is 9800/8/305 = 4, so array 1 should output 4 x 9 x 305 = 11,000 Wh. Keep playing with array 1 until you see that plus or minus a few percent.


There can be an efficiency bonus to higher voltages, but usually that would be fairly small.
Also, MPPTs do have a minimum starting voltage so array 1 starts producing power after array 2 and stops before array 2, but that's probably minimal too.
I think that when one panel is malfunctioning (unless is just a little loss like 10-20%), it would pull down the output of the whole array a lot and not just 305W. If one panel in array 1 is producing 0W, then I think you would loose around 8-9% of total output.
 
Array #1 voltage might be too low for the MPPT to operate properly, rewire it 4s2p and keep the other panel as a spare.
 
That could be possible If you have a MPPT inverter instead of a controller. What I see is that Inverters are often rated on output and have a lower PV input limit. Then I also see that Controllers are more often sized to input and output or else it is clearly indicated on the model name. 100A is far above the max. current of your arrays and should be ok.

If he has two separate MPPT controllers, like two Victrons or the like, they are going to only pull however much their charge current number is going to allow.

If he has two 100/20 Victron MPPT at 12/24/48 volts.. they are going to allow a maximum solar wattage of say 240/480/960 watts (plus a bit more for the higher bulk voltages beyond 12/24/48). If his loads (batteries and other loads) allow the max, the two charge controllers are going to output the same wattage to his loads regardless of whether one has more panels available or not if they are already at the maximum output.

Knowing what his equipment is would really help.
 
I have 2 EPEVER 100 Amp Mppt 200v controllers connected to a 1000 amp bus bar. All the panels are 305w seraphim. I will have to check each panel to see if one if dead or just pulling in low.

 
I have 2 EPEVER 100 Amp Mppt 200v controllers connected to a 1000 amp bus bar. All the panels are 305w seraphim. I will have to check each panel to see if one if dead or just pulling in low.

What is the voltage of your battery array? The part below in bold is the part that might be causing your issue.

MPPT Solar Charge Controller 100A EPEVER Tracer 10420AN
Rated charge current :100A
Max. PV open circuit voltage:200V(at minimum operating environment temperature) 180V(at 25℃ environment temperature)
MPP voltage range:V(BAT)+2V~144V
Max. PV input power: 1250W/12V battery, 2500W/24V battery , 3750W/36V battery, 5000W/48V battery system
 
What is the voltage of your battery array? The part below in bold is the part that might be causing your issue.
24v system but I'm only getting about 2200w from each array. The larger array should be getting the full 2400w.
 
24v system but I'm only getting about 2200w from each array. The larger array should be getting the full 2400w.

8 panels x 305 watts/panel x insolation of 4 = 9760 wh/d

If all you're getting is 2200 wh/d then both arrays have problems.

If you're looking at a "watt" number (e.g., 8x305=2400) on your system then you don't know if the system is performing as expected because it depends on a lot of factors (air mass, temperature, tilt, angle, time of day, etc. ... although 2200 sounds pretty good). Watts might do to compare two strings at the same time, but not to give you an idea as to how well they're working.
 
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24v system but I'm only getting about 2200w from each array. The larger array should be getting the full 2400w.
As you mentioned earlier; measure each panel, but before you get into such adventure, measure the voltage of both arrays when connected and under sun. Then please let us know the results.
 
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