Solaredge inverter and combiner

[hhsting]

Attached sketch shows following going into SE 43.21KUS:

1. 3 strings of 16 modules 8 optimizer per string
2. 3 strings of 16 modules 8 optimizers per string
3. 1 string of 16 modules 8 optimizers per string
1 string of 18 modules 9 optimizers per string


Total of 8 strings go to inverter but separated into less than or equal to 3 strings. Not sure if grouping like as shown total of 3 groups makes difference if each group is isolated from each other or not. The question is designer is not showing any combiner boxes. Do they need combiner boxes? If no why not and if yes then why.

 

[jaggedben]

SolarEdge will say no, but NEC may say yes. Let's see if we can find a past thread on this, there's been at least one.

 

[jaggedben]

Here's one you started two days short of a year ago.
https://forums.mikeholt.com/forum/ac...e-string-fuses

Here's another:
https://forums.mikeholt.com/forum/ac...than-2-strings

 

[hhsting]

I understand that one group of 3 strings going to one inverter solar edge may not require combiner according to manufacturer but the main question is post #1 attachment show 3 groups of 3 strings or less but the total strings are 8 going to one inverter. Manufacturer white paper shows one group of three strings to one inverter so total is three strings to one inverter correct me if I am wrong. I am not sure how many DC inputs one solare edge inverter have more than six. Where does manufacturer white paper address or say multiple groups of three strings or less into one Solaredge inverter not needing combiner? Would combine into multiple groups of three strings or less exclude need for combiner?

 

[Carultch]

I understand that one group of 3 strings going to one inverter solar edge may not require combiner according to manufacturer but the main question is post #1 attachment show 3 groups of 3 strings or less but the total strings are 8 going to one inverter. Manufacturer white paper shows one group of three strings to one inverter so total is three strings to one inverter correct me if I am wrong. I am not sure how many DC inputs one solare edge inverter have more than six. Where does manufacturer white paper address or say multiple groups of three strings or less into one Solaredge inverter not needing combiner? Would combine into multiple groups of three strings or less exclude need for combiner?

On the Synergy series Solaredge inverters, the strings are connected in groups of 3, which are not interconnected on the DC-side. Each group of 3 is wired to a separate power stage. The AC outputs are then paralleled within the primary unit, for a combined branch circuit. Each group of 3 strings should be treated as if it is connected to a completely separate inverter.

 

[BillK-AZ]

With the SolarEdge system the inputs are a series string of optimizers. These are basically isolated DC/DC converters. The PV modules are not in series in the classic sense. For multiple parallel strings, fused combiners may be needed to protect conductors from over current due to parallel strings. In the older designs with series connected modules, string fuses are needed to protect both conductors and bypass diodes.
Wire size is fixed as the optimizer cables are permanently connected to the optimizers.
Also, the optimizers do not allow a reverse current, but faults in home runs could produce higher currents from parallel strings. Most faults would be detected and result in rapid shutdown.

 

[ggunn]

With the SolarEdge system the inputs are a series string of optimizers. These are basically isolated DC/DC converters. The PV modules are not in series in the classic sense. For multiple parallel strings, fused combiners may be needed to protect conductors from over current due to parallel strings. In the older designs with series connected modules, string fuses are needed to protect both conductors and bypass diodes.
Wire size is fixed as the optimizer cables are permanently connected to the optimizers.
Also, the optimizers do not allow a reverse current, but faults in home runs could produce higher currents from parallel strings. Most faults would be detected and result in rapid shutdown.

SolarEdge's opinion is that combining three strings does not necessitate having string fuses, but some AHJ's do not agree.

 

[Carultch]

SolarEdge's opinion is that combining three strings does not necessitate having string fuses, but some AHJ's do not agree.

Initially, SolarEdge didn't even have 3 terminals in their inverters, and if you had more than 2 strings, you'd have to parallel the strings outside the unit. For lack of additional information, this would be done in a DC combiner with fuses on both polarities.

At one point, SolarEdge inverters came standard with 3 pairs of fuses, for inverter sizes where they anticipate 3 strings will be connected. So that would be 10kW single phase, 11.4kW single phase, 14.4kW 3-phase 208V, and 33.3 kW 3-phase 480V units, all of which you expect to connect 3 strings, would have 3 pairs of fuse holders within.

Now, because they have studies and documentation on how the reason for fusing 3+ strings on ordinary source circuits, doesn't apply to their DC optimizer strings, they have omitted fuses inside the inverter in all sizes, and have documentation to allow you to connect directly to the unit, should your AHJ accept it.

 

[ggunn]

Now, because they have studies and documentation on how the reason for fusing 3+ strings on ordinary source circuits, doesn't apply to their DC optimizer strings, they have omitted fuses inside the inverter in all sizes, and have documentation to allow you to connect directly to the unit, should your AHJ accept it.

Yes, I know, but when we showed the documentation to the Austin Energy solar department, they would not accept it because it wasn't a third party evaluation by a recognized testing authority. Also, the last time I checked the 11.4kW SolarEdge inverters still had the three fused inputs. It's been a while, though.