Solar DC wiring

[wizardket]

Ahhh!!! Now I see what the series question affects!

So what I would have are multiple sets of conductors with 10.5Adc, 566V on each of them going to the combiner(s) that are inside the inverter, right? So I have 15 sets of 2#12 (CU) + 1#12ground in a 1/2" conduit, all going to the inverter's combiner(s) because I have 15 strings. Am I catching a clue now?

Are you sure that the string combiners are "in" the inverter? Or are the combiner boxes separate and combine several "strings" (each fused) into one output (V=string V and A = #strings X panel Amps (plus agj)) that is then sent to the inverter? You would have a different wire size here. There can also be multiple combiners sent to one inverter (if it has a multi-lugged bus) as long as that combination does not exceed the inverters ratings. Also there is line loss on the DC feed to account for from the combiner to the inverter if they are not near by.

 

[mlnk]

So are the final numbers:

13 panels,modules in series:
8.42 x 1.25 x 1.25 = 13.2 amps
36.9 volts x 13 = 480 volts

Combiner will connect 5 strings:
5 x 13.2 amps = 66 amps

So what ambient heat factor is to be used?

 

[Article 90.1]

I'll put a note of caution out there.

The inverters we are using (PV Powered) have a maximum input voltage of 500 VDC. The Sharp panels that we have installed lately are consistently generating 10% above rated voltage, and this has been during 90-100 degree days in our area (East TN) which is close to the "hottest day calculation. The concern is that even though our string calculations come in below the 500 inverter threshold, that when we reach our coldest days we may be close to, or exceed the 500 VDC max. inverter input, thus voiding the warranty.

Of course, we are using all of the NEC 690 calculations, derating, etc. in our initial calculations, which allow some headroom on either side of the equation; our trouble, however, is that the Sharps are generating more DCV than expected/rated.

Is anyone else seeing these issues come up in their designs?

 

[iwire]

The Sharp panels that we have installed lately are consistently generating 10% above rated voltage,

Just curious but do you know that the meter being used to measure the voltage is accurate or is it consistent using different meters?

 

[Article 90.1]

iwire,

Good question. The answer is that I don't know if our meters are accurate, because they have never been tested against anything besides other meters. the higher than expected readings are being seen by multiple EC's who are using the same supplier and modules that we are, though.