PV size validation

[MaikaiLifeDIY]

Just wanna ping the forum to see what you think and any guidance.

In this scenario, I have an EG4 6000 EX which has the following PV limits.

Watts: 7500
Volts: 500
Amps: 27
Mppt: qty 1

Panels: Sunpower 305 Watt Solar Panel Model: SPR-305EL-WHT-D
Voc 64.2
imp 5.58

My basic calculation (not accounting for all parameters) shows a 7s3p would be the maximum for this combination of panels and inverter.

each string would be 449.4v at 5.58 amps for a combined output of 449.4v at 16.74 amps.

My question is; 21 panels at 305 stated watts a panel = 6405w. But if I use the formula "volts * amps = watts" (449.4 x 16.74) = 7522w, which is higher than the specified 7500 for the inverter.

Which value do you use and or what would be, if possible, a better configuration of these 305w panels to maximize the PV production on this EG4 6000 EX. I'm also looking for anything I'm overlooking, please critique my work!

Thank you in advance!

 

[MisterSandals]

But if I use the formula "volts * amps = watts" (449.4 x 16.74) = 7522w, which is higher than the specified 7500 for the inverter.

The watt calculation uses Vmp and Imp (the working values)

• Voltage - 54.7V
• Current - 5.58A

54.7V x 5.58A = 305.2W x 21 panels = 6410W

Overpaneling in terms of watts is just fine and quite common. It will help production in low light conditions (up to 7500W).

 

[MaikaiLifeDIY]

The watt calculation uses Vmp and Imp (the working values)

• Voltage - 54.7V
• Current - 5.58A

54.7V x 5.58A = 305.2W x 21 panels = 6410W (your SCC will clip this to 6000W)

Overpaneling in terms of watts is just fine and quite common. It will help production in low light conditions (up to 6000W).

I just realized I put in the wrong values, but I'm gonna leave the original post as is so others can learn from my mistake.

So the question I still have, is whether there is a better combination of this specific panel that will yield a higher output of PV?

 

[MaikaiLifeDIY]

Now that I have the math correct, I'm showing a 5s5p would yield 7625w, would that be okay for the overpaneling amount you mentioned?

Or would 6s4p be better since it's under a little?

 

[MisterSandals]

I'm showing a 5s5p would yield 7625w,

5S5P is 25 panels

305W x 25 = 7625W yep

Arranging your panels differently does not change the watts, it only changes the array volts and amps.
''your primary panel configuration should be for getting the voltage into the upper half of the MPPT (optimized) range. And NEVER exceed max input voltage.

 

[MaikaiLifeDIY]

5S5P is 25 panels

305W x 25 = 7625W yep

Arranging your panels differently does not change the watts, it only changes the array volts and amps.
''your primary panel configuration should be for getting the voltage into the upper half of the MPPT (optimized) range. And NEVER exceed max input voltage.

What about the max amperage, the inverter lists 27, but with 5s5p, that puts me at 27.9, but my voltage is still under 500? Can the amperage be over slightly or is that a hard limit live the voltage?

 

[MisterSandals]

What about the max amperage, the inverter lists 27, but with 5s5p, that puts me at 27.9, but my voltage is still under 500? Can the amperage be over slightly or is that a hard limit live the voltage?

5S = 64.2Voc x 5 = 321V the Voc is used as the no load value like in the early morning when sun first hits your panels and the SCC has not started pulling power. Once the SCC starts pulling power, the voltage will drop closer to the Vmp, depending on what the MPPT search determines to be optimal.

When the SCC is working, the Vmp should be within the MPPT (optimized!) range for best results.
For this, 54.7Vmp x 5 = 273.5V
This is on the low side and when its in low light conditions, (early morning, slightly overcast, evening) your SCC may not have enough volts to run or produce anything.

You should strive for as many in series as possible to keep your temp corrected Voc below 500V (max input voltage).

What is the lowest temperature your array will have?

 

[MaikaiLifeDIY]

5S = 64.2Voc x 5 = 321V the Voc is used as the no load value like in the early morning when sun first hits your panels and the SCC has not started pulling power. Once the SCC starts pulling power, the voltage will drop closer to the Vmp, depending on what the MPPT search determines to be optimal.

When the SCC is working, the Vmp should be within the MPPT (optimized!) range for best results.
For this, 54.7Vmp x 5 = 273.5V
This is on the low side and when its in low light conditions, (early morning, slightly overcast, evening) your SCC may not have enough volts to run or produce anything.

You should strive for as many in series as possible to keep your temp corrected Voc below 500V (max input voltage).

What is the lowest temperature your array will have?

The lowest temperature is about 40 Fahrenheit, highest would be about 140 Fahrenheit.

 

[pvgirl]

Make sure you adjust Voc for lowest possible temperature, Voc will go up to 69 volts at 0c/32f

 

[MisterSandals]

The lowest temperature is about 40 Fahrenheit, highest would be about 140 Fahrenheit.

Ok, not much of a concern then.

I'd shoot for:
6S = 64.2Voc x 6 = 385V
54.7Vmp x 6 = 273.5V

7S = 64.2Voc x 7 = 449V (very safe in regards to max input voltage)
54.7Vmp x 7 = 382V (fairly low in MPPT range)

8S = 64.2Voc x 8 = 513V (too high!)

 

[Supervstech]

Yup, unless shading is a concern, I’d setup in 7s configuration.

You may want to have a set facing east, and a set facing west to boost morning and evening output.

With 140F highs, I’d guess the panels don’t produce much in full summer direct angle anyway…

 

[MaikaiLifeDIY]

Okay, just to confirm I'm following correctly.

The ideal size would be 4 strings of 7.

7s4p using Voc would be 449, still safely under the 500 limit for the MPPT on the EG4 6000 EX

7s4p using Vmp would produce the following results, giving more wattage than what is needed but better for mornings/evenings to over panel?

Volts	Amps	Watts
382.9	22.32	8546

Did I follow you correctly?

 

[MisterSandals]

The ideal size would be 4 strings of 7.

With 28 panels yes, 7S4P.
With 21 panels, 7S3P.

Either way, you will need to fuse each string when 3 or more are combined in parallel. A 4 string combiner box is mighty handy for fusing and cutoff capability.

Something like this:

Amazon.com

 

[MaikaiLifeDIY]

With 28 panels yes, 7S4P.
With 21 panels, 7S3P.

Either way, you will need to fuse each string when 3 or more are combined in parallel. A 4 string combiner box is mighty handy for fusing and cutoff capability.

Something like this:

Amazon.com

Okay so if you have more wattage than what the inverter can use for example a 7s4p configuration, that is fine so long as the amps and volts are under the maximum for the inverter??

Again thank you so much for your responses, I feel like I knew this stuff in theory, but the practicality of chatting back and forth has really calrfied things for me so far. I understand the fuses also, I will certainly have something similar in place.