Growatt SPF5000ES - efficiency depending on panels count

[solarrig]

Hello,

I can't find information on Growatt efficiency depending on Voltage per string. I will give example:
Lets say solar panel is 400W; 38V (Voc)
Growatt max PV input is: 450V

Situation1: 11pcs. of these panels connected to one inverter 11x38V = 418V and 4400W (let's call it 100% efficiency)
Situation2: 5pcs. of these panels connected to one inverter 5x38V = 190V and 2000W (lets call it 45%) + 6pcs. of these panels connected to 2nd inverter = 6x = 228V and 2400W (55%)

My main question is about maximum efficiency: will those two inverters, that have 5 and 6 pcs. of panels will perform proportionally less? Or because of the much lower PV Voltage, they will not give the same amount, and sum of two will not reach 4400W? And sum will only give me lets say ±80%.

From here i have 2nd question.
Is it better for inverter longevity to work near the maximum load, let's say 430V (out of 450V). Or it is better to load it at 350V, then it will work easier, less heat, longer live?

Thank you.

 

[BentleyJ]

Situation1: 11pcs. of these panels connected to one inverter 11x38V = 418V and 4400W (let's call it 100% efficiency)
Situation2: 5pcs. of these panels connected to one inverter 5x38V = 190V and 2000W (lets call it 45%) + 6pcs. of these panels connected to 2nd inverter = 6x = 228V and 2400W (55%)

This question has a 2 part answer, theoretical and practical. Since the MPPT charge controllers have an algorithm that produces the maximum output for any given Voltage & Amperage PV input (within the published MPPT ranges) based on immediate solar conditions, situation 1 and situation 2 should be virtually identical.

In reality the Growatt may have some internal quirks that testing of both situations would show one is better than the other. Perhaps other Forum members that use that brand could give some first hand experience.
Situation 1 is most likely slightly better because the higher voltage string will start producing earlier in the day and continue producing later in the afternoon when the sun angles are unfavorable. Before chooing this option, its necessary to calculate Voc at the lowest temperature expected for your region. Reason is because Voc increases as temp. goes down. The datasheet should have the voltage-temp coefficient listed. Something like -0.3% per degree C.
Also, Situation 1 would only require 1 Pos and 1 Neg wire from the PV array to the inverter. Situation 2 would require 4 wires. Plus the equipment ground of course.

From here i have 2nd question.
Is it better for inverter longevity to work near the maximum load, let's say 430V (out of 450V). Or it is better to load it at 350V, then it will work easier, less heat, longer live?

Heat generated by a circuit is given by: Watts = Amperage(squared) x Resistance in ohms. Therefore it is clearly better to use higher voltages and less amperage.

 

[timselectric]

My panel VOC is 37v. I run 10 panels in series for 370v total VOC. In Kentucky, this has proven to be the sweet spot for this unit. I tried 11s and the bus voltage got too high in winter. On a normal sunny day, my array voltages are around 300v.

 

[Vigo]

Situation #1 is highly preferable because the Growatt has a minimum operating voltage of 150v which means it basically wont harvest solar at 150v or below.

 

[timselectric]

It requires 150v to wake up. But can produce at as low as 120v. Although you wouldn't get full capacity that low.

 

[Vigo]

It may simply be because 150v is further from max power voltage point on my higher volt arrays, but by casual observation (no logging) it seems to me that as soon as it drops below 150v it quickly tanks to ~90v, releases, and does that over and over again until it gives up on solar for the day. So in my case it seemed 150 was pretty close to the practical ‘limit’. Its possible if i hooked a lower volts array where 120v wasn’t so far below max power voltage, it would sit there happily and produce. Makes sense in my head, anyway.

 

[timselectric]

Hard to say. Technology can be a fickle bitch sometimes.

 

[LydMekk]

Most of the current MPPTs in todays units seem to have a sweetspot around 370V for max efficiency.
All Voltronis/MPP/EG4 etc. follow this "recipe" (I'm wondering if they buy a certain common chipset)...

 

[solarrig]

This question has a 2 part answer, theoretical and practical. Since the MPPT charge controllers have an algorithm that produces the maximum output for any given Voltage & Amperage PV input (within the published MPPT ranges) based on immediate solar conditions, situation 1 and situation 2 should be virtually identical.

In reality the Growatt may have some internal quirks that testing of both situations would show one is better than the other. Perhaps other Forum members that use that brand could give some first hand experience.
Situation 1 is most likely slightly better because the higher voltage string will start producing earlier in the day and continue producing later in the afternoon when the sun angles are unfavorable. Before chooing this option, its necessary to calculate Voc at the lowest temperature expected for your region. Reason is because Voc increases as temp. goes down. The datasheet should have the voltage-temp coefficient listed. Something like -0.3% per degree C.
Also, Situation 1 would only require 1 Pos and 1 Neg wire from the PV array to the inverter. Situation 2 would require 4 wires. Plus the equipment ground of course.

Heat generated by a circuit is given by: Watts = Amperage(squared) x Resistance in ohms. Therefore it is clearly better to use higher voltages and less amperage.

Yes, thank you. That's what i though!

Good point regarding winter.

 

[solarrig]

Most of the current MPPTs in todays units seem to have a sweetspot around 370V for max efficiency.
All Voltronis/MPP/EG4 etc. follow this "recipe" (I'm wondering if they buy a certain common chipset)...

That's very interesting point !!!