Firstly, I'm new to this forum - so Hello to everyone.

I have a question on string voltage calculations, but some background first.

I am removing my current GT ABB Uno as it does not support batteries and can no longer connect to grid as NRS is 2010 and not 2017. I have 10x 250w on string 1, and 12x 260w on string 2. (This is important as I'm concerned I might over voltage later).

My new setup (installed but not commissioned).

• 2x Deye 5kw Hybrids in Parallel.
• The 2 existing PV strings to inverter 1 (Master) = 5600w = under the 6500max wattage supported by Deye 5kw & both strings under 50% of max.
• Two new strings (400w x 6 / 400x 4) to the second Deye (Slave) = 4000w = under 6500max wattage & both strings under 50% of max.

My challenge (and lack of understanding).

The Deye supports up to 500v PV input (or 100-500v as per manual specs). When I put testers on the DC strings during final inspection, I noted that string 1 (3200w/12 panels) is running at nearly 420v and string 2 (2500w/10 panels) is running at just over 330v. Not sure if this is important both both strings are running DC TS4 Optimisers on every panel due to shade issues.

SOOOOO - My question:

• If the inverter supports 500v DC PV input, is this per MPPT or MAX (both strings / mppt's combined).
• If MAX, I am summing then that I am over paneled (even though under wattage) and I might damage the inverter?
• If per MPPT, then I am under max voltage and safe?
• SO - which one is it?

I don't want to turn my inverters on in case I am over voltage on DC, and I cannot find an answer on Google - PLEASE HELP?

Thanks,

Andy

Good Morning and welcome to the forum.

The Deye inverters support 500v max per MPPT. To be save never exceed 450v per MPPT. 

I am not a guru but looking at your figures you should be fine 

After many discussions with Sunsynk/Deye, best is for Voc total not be more than 450 volts, I was installing ten panels for a total Voc of 468 volts, which would be ok 99%  of the time, but then decided not to take a chance on even 1% and backed down to 9 panels

Hi again and thanks for the replies. Most grateful.

OK - I will get the installer to test Voc again this morning and make sure that Voc is under 450 per string.

Another question. I know that Wattage varies during the day. How much is voltage expected to vary during the day. Does Voc rise with sun angles the same way Wattage rises? (or is Voc constant per panel?)

Thanks,

Andy 

@AndyFyou measure Vmp not Voc and it it shows on your inverter, no need to measure it at the panels, post the datasheets for the 250 watt and 260 watt panels, maybe we can then give you a better answer.

Andy  on my system the voltage rises and then stay constant with a couple of volts up and down then drops again at night. The amps vary a lot.

 

Like Tariq commented the Vmp is what will be measured by the inverter. The VOC is the maximums that will be achieved with no load, You will get a lower voltage when the panels is connected 

 

Edited August 5, 20214 yr by Krokkedil

37 minutes ago, Tariq said:

@AndyFyou measure Vmp not Voc and it it shows on your inverter, no need to measure it at the panels, post the datasheets for the 250 watt and 260 watt panels, maybe we can then give you a better answer.

Hi Tariq

Spec sheet for Yingli 60 cell 35mm series 250w (YL250P-29b) is 

• Imp 8.39A
• Vmp 29.8V
• Isc 8.92A
• Voc 37.6V

Spec sheet for Yingli 60 cell 35mm series 260w (YL260P-29b) is 

• Imp 8.59A
• Vmp 30.3V
• Isc 9.09A
• Voc 37.7V

The total Voc on your 12X260 watt string is 452 volts, you are right on the border you should be safe and the 12X250 watt string is 451 volts, also safe. It is PER mppt, you don't combine the two string voltages.

AND

12X260= 3120 watts for first string

12X250= 3000 watts for second string

perfect for the first inverter

Thanks everyone. Advice greatly appreciated.

Will run final tests at midday peak sun with meter and do a last double check on wiring of entire house change over and inverters, then turn on inverters for first time 👍

Feedback:

Changed the strings a bit and now have string 1 running at 371v peak and string 2 running at 367v peak. (Gotta love DC Optimisers)...

Both strings are now an almost perfect match on both voltage outputs, and at 369v +-2v common, I am well under the 425v indicated on the side of the inverter and 450v indicated as preferable max by many forum users, and also have plenty of margin for when panels boost volts at low temp coefficients...

Happy and 1st inverter successfully commissioned.

Again, a big thumbs up to everyone who chipped and and helped. Appreciated