Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-6000

So I am designing a 6KWH grid tied solar system for a home owner. This is the first one I've designed with dual MPPT, I have only designed one prior to this that was single MPPT sunny boy US7000.

The panels that I selected were Canadian Solar CS6P-255M, total of 24 panels for 6120watts for the power one aurora inverter.

Now the panel over current (ISC) is rated at 8.74amps, there will be 2 strings of 6 panels each dedicated to each mppt.

So my new combined number per MPPT is 17.48 (ISC), I then multiplied that by the DC over currrent rating of 35% for over current fuse protection and I come up with 23.598 amps.

So I am reading over the specifications of the Power One Aurora PVI-6000OUTD

The language is some what confusing.
It says Number of DC Inputs 2(1 mppt)
It then says MAX DC Current 18(22 short circuit) This is the confusing language!?!?!?!
It also says DC disconnect rated for 25amps

So what language am I to follow? MPPT MAX current, or DC disconnect over current rating?

My question is are these panels within specification for the over current rating of the aurora. As I am confused with the spec language when power one says MAX I am assuming its always ISC, and to follow the MPPT rating not necessarily the disconnect rating..

I don't want to have to replace these fuses during a cold winter. Would it be better to use the canadian solar 250's vs the 255's due to these specs.

Please Help and Thank You

Comments

  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    I don't want to have to replace these fuses during a cold winter. Would it be better to use the canadian solar 250's vs the 255's due to these specs.

    For one thing, cold weather increases module voltage, not current.

    For another, the inverter will take what current it can handle and clip the rest.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    Why are you doing 2 strings of 6 modules per input? You should do strings of 12. Overcurrent problem goes away, more efficient and lots less wire too.
    Besides, with 2 strings of 6, no fuses are needed, and the 25% (not 35%) overcurrent rule does not apply - so the inverter's 18 amp spec is sufficient for the 17+ Isc.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    ggunn wrote: »
    For one thing, cold weather increases module voltage, not current.

    For another, the inverter will take what current it can handle and clip the rest.

    Thank you for the correction, level of sunlight irradiance increases amps, temperature reflects voltage output.

    So in reference to the specifications do I go by 18 or 22 since ISC of panel is 17.48? Or should be I concerned with with the short circuit number of 22 when I calculate by 35%?
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    solarix wrote: »
    Why are you doing 2 strings of 6 modules per input? You should do strings of 12. Overcurrent problem goes away, more efficient and lots less wire too.
    Besides, with 2 strings of 6, no fuses are needed, and the 25% (not 35%) overcurrent rule does not apply - so the inverter's 18 amp spec is sufficient for the 17+ Isc.

    strings of 6 rather than strings of 12 so that a string of 6 panels is less effected by shading. There is a large tree and chimney on the south east corner of the home. So if I have a string of 12 and one panel is effected by the shade of the chimney or tree "all" 12 modules would be effected by production. So in early morning only a string of 6 would be affected rather than a string of 12, provides healthier number, by separating individual strings. Dual MPPT is being used so that east bound panels, can make production and separate from the south bound panels. 6 of the east bound panels would get shade from the vent pipe that sticks out of the roof.

    That was the reason for smaller strings.

    As far as fuses are concerned I always use fuses(ALWAYS) for liability and warranty I always install them, and I have always calculated 35% for DC and 25% for AC.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    Six panels with a Vmp around 30 will give the array an output of about 180 Volts.
    That probably isn't high enough for the inverter to run from. Check the specs, as most central GT inverters need around 300+ Volts to operate.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    Six panels with a Vmp around 30 will give the array an output of about 180 Volts.
    That probably isn't high enough for the inverter to run from. Check the specs, as most central GT inverters need around 300+ Volts to operate.


    The specs say that it is set for "200V nominal" but it is adjustable as low as 120V and as high as 350V, and MPPT full power starts at 170V.

    Attachment not found.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    Even with modules in strings of 6, you will suffer shading effects on the 12. When one set of 6 is dragged down by shading, the MPP tracking will find the max point is at a lower voltage than what the good string of 6 would optimally desire. Plus the inverter (even if you set the start voltage lower) will not be as efficient as with strings of 12. The Aurora is unusual in letting you use strings of 6 in the first place. All other GT inverters want 8 or 9 modules per string minimum. If the string voltage is greater than the AC output voltage, it only has to downconvert the voltage, and is more efficient. You may want to consider one of the distributed type inverters like SolarEdge or TIGO if you have significant shading.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    The specs say that it is set for "200V nominal" from the factory but it is adjustable as low as 120V and as high as 350V, and MPPT is activated at 170V. I was considering setting the activation to 170V.

    Attachment not found.

    Only 350 Volts max? In that case you can't have a string of 12 as that would be too high.
    I don't think I like that inverter's specifications very much. It seems to rely on current over Voltage, which is sort of backwards of the preferred way to get power.
    If this thing is rated as 6kW, then you see 6000 Watts / 18 Amps max in = roughly 334 Volts. You're planning four strings @ 8.5 Amps? I see what you mean about the confusion. Is that input current max for each input or the combined?

    Any chance the company has a string sizing tool for its products?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    That was weird: the spec sheet didn't show in the original post but did when I quoted it.
    Now I suppose we have to figure out why.

    Anyway, at least we know it's 18 Amps per input! :D
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    Only 350 Volts max? In that case you can't have a string of 12 as that would be too high.
    I don't think I like that inverter's specifications very much. It seems to rely on current over Voltage, which is sort of backwards of the preferred way to get power.
    If this thing is rated as 6kW, then you see 6000 Watts / 18 Amps max in = roughly 334 Volts. You're planning four strings @ 8.5 Amps? I see what you mean about the confusion. Is that input current max for each input or the combined?

    Any chance the company has a string sizing tool for its products?

    Specs are confusing. The implication of these specs is that the inverter can be set to activate from around 120V to 350V, thats just inverter start up.
    The spectrum of operation for the MPPT is from 170V to 580V, which I would think that the inverter is a 600V max inverter, however if it were me I would only want the operation according to the MPPT operation range of 170V, to 580V being that this system has a couple of shading factors.
    I believe when it says 2 inputs @ 18MAX I believe that is a division problem which means 9 amps per input channel is what it is capable of being "combined", via the 2 input channels per mppt. I some what don't like that feature as it makes the builder rely on the aurora disconnect where as in the case of the sunny boy7000US I install it has a "combined "channel for combined string via a external combiner box which can offer higher over current ratings instead of independent 12amp fused channels of the sunny boy disconnect, so there are more options essentially with the sunny boy disconnect VS the power one disconnect.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    no no, the 350V spec is the maximum setting for the input activation (or startup) voltage - not the max input (which is 600V) or max MPPT (which is 530V).
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    2 inputs @ 18A means 18A each input. You can put 2 strings on each input. But my recommendation having installed a bunch of these is to do a string of 12 on each input. Solve the shading problem by either doing whatever you have to to not put modules in the shade or use a TIGO converter on the modules that have shading.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    solarix wrote: »
    Why are you doing 2 strings of 6 modules per input? You should do strings of 12. Overcurrent problem goes away, more efficient and lots less wire too.
    Besides, with 2 strings of 6, no fuses are needed, and the 25% (not 35%) overcurrent rule does not apply - so the inverter's 18 amp spec is sufficient for the 17+ Isc.
    Even with four strings fuses should not be needed if they are divided between two MPPT inputs.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    ggunn wrote: »
    Now that I think about it, even with four strings fuses should not be needed since they are divided between two MPPT inputs.

    For protection of equipment and the fact I have a 10 year labor warranty against installation its cheap insurance to have the consumer pay for a DC breaker box or fuse box. If the consumer doesn't want it, I don't install it. I don't prefer customers coming after my bond, or 2 million aggregate insurance policy. I install for .98 cents per watt so its not like I'm getting rich from these installations.

    Its a great piece of mind to just install an over current device.

    NEC code is also recognized as the bare minimum requirements, over current protection on equipment over $1000 is a big deal to me. Even SunnyBoy inverter/disconnects come with 5/8/12 amp fuses per input channel, why power one didn't include it for piece of mind boggles me because it is essentially very inexpensive to ad it and protect the equipment.

    No where in the wiring diagram does it show over current fused/breaker protection on DC side. To me that's a big deal for any system whether its a 1 amp draw or an infinitely higher number.
    Attachment not found.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    For protection of equipment and the fact I have a 10 year labor warranty against installation its cheap insurance to have the consumer pay for a DC breaker box or fuse box. If the consumer doesn't want it, I don't install it. I don't prefer customers coming after my bond, or 2 million aggregate insurance policy. I install for .98 cents per watt so its not like I'm getting rich from these installations.

    Its a great piece of mind to just install an over current device.

    NEC code is also recognized as the bare minimum requirements, over current protection on equipment over $1000 is a big deal to me. Even SunnyBoy inverter/disconnects come with 5/8/12 amp fuses per input channel, why power one didn't include it for piece of mind boggles me because it is essentially very inexpensive to ad it and protect the equipment.

    No where in the wiring diagram does it show over current fused/breaker protection on DC side. To me that's a big deal for any system whether its a 1 amp draw or an infinitely higher number.
    Attachment not found.

    You understand that string fuses are not there to protect the inverter, but the strings themselves, right? PV modules are current self limited and the inverter uses the MPPT circuit(s) to limit the current it draws from the array. Even if you dead short the output circuit of a combiner box when the array is putting out its peak power, the string fuses will not blow.

    String fuses limit the fault current that other strings wired in parallel to a faulted string can feed to the fault, and if there are only two strings, only one string's worth of current can come into the circuit and that current will below the blow point of the fuse. You can fuse two strings in parallel if you want (the code does not prohibit it) but those fuses will never do anything.

    My comment about not having to fuse the four strings was because since each MPPT input would only be connected to two strings, each of the four strings would not have current paths to all the other strings, just the one with which it shares an input. Verify that, of course.
  • shortcircuitshortcircuit Registered Users Posts: 3
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    The PVI 6000 TL must be connected to an ungrounded array.

    shortcircuit
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    The PVI 6000 TL must be connected to an ungrounded array.

    shortcircuit
    There is sometimes confusion about what is meant by an ungrounded array. It means that neither the DC+ or DC- conductor(s) are connected to ground inside the inverter, but both DC+ and DC- PV source circuit conductors are fused, and DC+ and DC- is switched by the DC disconnect. It does not mean that the module frames and metal racking are not grounded; they take an Equipment Grounding Conductor, the same as a grounded array.
  • shortcircuitshortcircuit Registered Users Posts: 3
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    ggunn wrote: »
    There is sometimes confusion about what is meant by an ungrounded array. It means that neither the DC+ or DC- conductor(s) are connected to ground inside the inverter, but both DC+ and DC- PV source circuit conductors are fused, and DC+ and DC- is switched by the DC disconnect. It does not mean that the module frames and metal racking are not grounded; they take an Equipment Grounding Conductor, the same as a grounded array.

    I agree. But there is a problem in our area regarding this. With the efficiency of the transformer-less inverter, more and more installers are using them but are unaware of proper wiring practice associated with the array.

    Is the PVI 6000 CSA listing ok in the USA?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    I agree. But there is a problem in our area regarding this. With the efficiency of the transformer-less inverter, more and more installers are using them but are unaware of proper wiring practice associated with the array.

    Is the PVI 6000 CSA listing ok in the USA?
    It's on the CEC list (http://www.gosolarcalifornia.ca.gov/equipment/inverters.php), if that is what you are asking.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    ggunn wrote: »
    It does not mean that the module frames and metal racking are not grounded; they take an Equipment Grounding Conductor, the same as a grounded array.
    Or a Grounding Electrode Conductor, depending on the setup. :-)

    If you use microinverters, for example, the AC ground is supplied by an EGC inside the wiring harness, while the DC ground and lighting ground for the panels and racking is supplied by a separate GEC to the DC ground point. (Which will in turn be bonded to the AC ground point somewhere.)
    SMA SB 3000, old BP panels.
  • shortcircuitshortcircuit Registered Users Posts: 3
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    ggunn wrote: »
    It's on the CEC list (http://www.gosolarcalifornia.ca.gov/equipment/inverters.php), if that is what you are asking.

    I was asking if CSA is acceptable in the USA like UL?
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    inetdog wrote: »
    Or a Grounding Electrode Conductor, depending on the setup. :-)

    If you use microinverters, for example, the AC ground is supplied by an EGC inside the wiring harness, while the DC ground and lighting ground for the panels and racking is supplied by a separate GEC to the DC ground point. (Which will in turn be bonded to the AC ground point somewhere.)
    All very true, of course. The point I was trying to make is that some folks incorrectly interpret "ungrounded array" to mean that the EGC/GEC is not required.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60
    I was asking if CSA is acceptable in the USA like UL?
    UL and CSA are both Nationally Recognized Testing Labs (NRTL) for US certification. But CSA can test to either US or Canadian standards.

    If the marking does not say CSA/US or similar and also does not reference a UL standard number, it has not been tested to US standards and cannot be used where UL or equivalent listing is required by NEC.
    SMA SB 3000, old BP panels.
  • BeeLineBeeLine Registered Users Posts: 1
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    I just registered to say thanks for this thread.

    I'm working on my own system today - and it's the first time I've used the Aurora. (PVI-6000) Per their string size calculator - 4 strings of 7 Trina Honey 250. With the dual MPPT and dual inputs per MPPT I was figuring on forgoing the string fusing and after reading this and giving it more thought I'm skipping it. Between the monitoring that takes place in the inverter and the diodes in the modules, I'm having a real hard time imagining a scenario in which the fuses would do anything. Not to mention my AHJ's insistence on a load-break device ahead of the fusing per NEC (I figured the load-break DC disconnect on the unit would suffice...) If my string sizes look odd, it's because I'm in hot as hell / cold as hell southern Colorado.

    If the OP happens to see this: I wouldn't hesitate to install the configuration you spelled out above if their string sizer agrees. If your short circuit current is below the max current, then there should never be an issue at max power current. I'd agree that their literature could use a little polishing up, though.

    Thanks again, all, for a good thread.
  • BB.BB. Super Moderators, Administrators Posts: 30,629 admin
    Re: Need help with over current protect (short Circuit Protection Specs) of AuroraPVI-60

    We are very happy that you find the information helpful and relevant.... For the most part, we try to stay on topic in the forum to keep the signal to noise levels high.

    Let us know how your installation works out and any issues you may run across.

    You can create your own thread to post your information.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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