Fuse for PV1 and PV2?

[Archos]

I have PV1 (7 panels serial) and PV2 (5 panels serial) all same brand with short circuit current of 14.10A and Max. Current at 13.30A.
System has 15A DC fuse for each PV.
I told installer that 15A is very near to open circuit current and he says: Because panels are in serial 15A is enough, and actually fuse is not needed but we installed it anyway.
Is that true or do I ask him to replace fuse with 20A or 25A?
Thank you for your comments, some technical docs of panel are attached for those experts.

 

[SeaGal]

No fuse needed for that configuration. The fuse won't even blow it if they are short circuited.

fuse is not needed but we installed it anyway.

That makes sense. Fuse not needed, but installer makes more profit by installing one

 

[Brucey]

You would only need a fuse/breaker if you have three or more strings in parallel.

 

[Archos]

Ok, Thank you all

 

[timselectric]

Is that true

Yes

 

[PVGeezer]

You are right to question what your installer has done. Not only is the fuse not required or needed but it's too small and should be removed.

All fuses and breakers (not just for PV) need to be sized for at least 1.25 x the continuous current expected in the conductor to avoid nuisance trips. PV circuits get an additional 1.25 factor for cloud reflection light enhancement. So in your case the minimum fuse size is 14.1 x1.25 x 2.25 = 22A. Next larger available fuse size is 25A.

Tell your installer he's in violation of Article 690 parts 8 and 9 of the NEC and needs to either remove the fuses or increase their size to avoid nuisance trips.

If he can't get something as basic as PV string fuse sizing right it makes one wonder what else might messed up. Did he use at least 12 AWG 75C rated wire on those circuits?

 

[Archos]

It is easy to change fuses with desired Amperage since they are like the ones below (attached picture).
For time being they are 15A, if they start nuisance trips I'll upgrade them to 25A. But as far as I have observed from datalogs, -because panels are in serials, only voltages change (0 to max) during operation, amperage is very stable with little high and lows and stays many digits away from the 15A fuse.

 

[PVGeezer]

Just first a small bit of nomenclature clarification here, your solar modules are said to be in "series" rather that in "serial".

I would suggest you go ahead and change the fuse size right away. 15A is too close to your Isc of 14.1 so I expect that the 15A fuses will blow pretty soon. If you were in the US and subject to our electrical code I would change them to 25A but in your case 20A will probably be OK. Please be sure your wire size is at least 4 mm2/ 12 AWG before you make the change.

Something is a little odd with your comment that the current (amps) isnt changing much but the voltage is. The current from a PV circuit normally varies in proportion to the amount of sunlight received by the modules, so that should be changing a lot throughout the day as the sun angle changes or clouds pass over. The voltage should be relatively constant, it goes up and down a little with the light level and with temperature, but not a lot.

If as you say you're seeing the opposite, current staying constant but voltage changing, then there is something limiting the output of your solar array.

Are your solar strings feeding into an MPPT battery charge controller? If so it could just be that your batteries are fully charged, causing the MPPT to limit the solar output by raising the voltage to reduce how much current your solar array produces. That's fine. You can confirm that by putting a large load on the batteries so the MPPT goes into full power mode. At that point the current from your PV strings should reach something near to the 13.3 amp Imp rating of the modules if it is around solar noon on a sunny day.

If your batteries aren't fully charged, or if youre feeding the grid through an inverter then your MPPT/ inverter might be undersized for your solar array. It protects itself from too much power input by pushing the voltage up and the current down, which would cause what you are seeing. Some undersizing of MPPTs can be ok, but it shouldn't be so low that the solar array current stays the same all day long.

 

[Archos]

Yes, I have a MPPT Smart Inverter which limits the output if my batteries are full and during normal load it stays between 4-8Amps. When I put large load, it starts to produce more and the max amps reaches 10-11.5A during a sunny noon. I have never seen 13A in datalogs in winter, maybe because of angle.

 

[PVGeezer]

It probably is low sun angle over the winter. The other possibility is that your solar array output is reaching the maximum capacity of the MPPT so it is protecting itself from being overloaded by limiting how much current the array is producing. Check the MPPT power rating to be sure it's a good match with your solar array.

As we move into spring you should see the current go up to around 13 amps or higher if you have some cloud reflection and your batteries aren't full. Then you will know you are getting full output from your solar array. That's also when it is likely that your 15A fuses blow if you haven't replaced them with higher rated ones.

 

[SeaGal]

Tell your installer he's in violation of Article 690 parts 8 and 9 of the NEC ....

I'd love to witness the installer in Turkey reacting to that

 

[PVGeezer]

Yeah I didn't see Turkey to start with. But electrons know no nationality. He's still doing it wrong if he's putting 15A fuses on 14 amp circuits.