VMP, IMP, VOC, ISC questions

[Ejimenez]

Panel specs are

Vmp: 34.9v
Imp: 13.19A
Voc: 41.8v
Isc: 13.92A



If im not mistaken inverter is rated for a MAX of 500VDC and MPPT voltage range of 90-450VDC, it says number of MPPT/Maximum Input Current is 1/27A.


im going for 18 of those panels so I am assuming I can make 2 9 panel series and then both series connect them parallel and thus would give me around (Using Voc) 376.2V and 26.38A which would work fine for the inverter specs right? (I assuming with cabling loss and temps of 80+(even 100F) would lower those values a bit more no? Do I need to consider isc with voc or its just voc with imp? If I use voc and isc for the calculation it would pass 27a easily. Would it be better to just upgrade the inverter to be safe? (im not doing this DIY but would like to be safe of what the installer/company is doing lol)

 

[sunshine_eggo]

9 * 41.8V = 376.2Voc
2 * 13.92A = 27.84A Isc

Looks good to me. I wouldn't sweat the 0.84A.

Provided the MPPT will actually USE up to 27A, and 27A isn't just an Isc limit (some have both limits), then 9S2P fits within the MPPT limits and should yield peak performance for the conditions, i.e., you haven't configured the array up against some limit on the input.

The charger must be capable of (assuming off-grid, 48V battery):

18 * 34.9 * 13.19A / 48V = 172A

This is a VERY high output from an MPPT. I'm not aware of any single MPPT that will output that much. You are likely overpaneling the MPPT.

If this is a grid tie inverter, then that's a different beast, and you may be fine on the output.

 

[Ejimenez]

9 * 41.8V = 376.2Voc
2 * 13.92A = 27.84A Isc

Looks good to me. I wouldn't sweat the 0.84A.

Provided the MPPT will actually USE up to 27A, and 27A isn't just an Isc limit (some have both limits), then 9S2P fits within the MPPT limits and should yield peak performance for the conditions, i.e., you haven't configured the array up against some limit on the input.

The charger must be capable of (assuming off-grid, 48V battery):

18 * 34.9 * 13.19A / 48V = 172A

This is a VERY high output from an MPPT. I'm not aware of any single MPPT that will output that much. You are likely overpaneling the MPPT.

If this is a grid tie inverter, then that's a different beast, and you may be fine on the output.

It's a hybrid inverter, it says max solar charging current 160A and max AC charging current 140A so that's what you mean by overpaneling the MPPT no? (172A vs the 160A).

This is the inverter, im thinking of asking them if there is another better one because I just want to be on the safe side, don't want to burn this out in 2 years lol, im trying to see if I can squeeze a 10kw system on the current budget (im 100% sure its doable if I go DIY but I honestly don't feel safe, ready nor confident to work on electrical stuff even more so high current/amps stuff)

On/Off-Grid Dc-Ac 7.2Kw 8.2kw 10.2kw 48V Mpp Hybrid Solar Inverter

· Pure sine wave solar inverter(on/off Grid)· Output power factor 1.0· WIFI&GPRS available for lOS and Android· lnverter running without battery· One-click restoration to factory Settings· Built-in Lithium battery automatic activation· Built-in 160A(for 7.2KW/8.2KW)/180A(for 10.2KW)MPPT...

szmysolar.com

 

[RCinFLA]

The 160 amps is battery line charging current and it depends on battery voltage. The maximum battery charging current is only at lower battery voltage.

From unit's weight specs, this is a HF inverter with a HV DC internal bus. All power is routed through this bus (with exception of AC input to AC output pass-through).

PV SCC is boost converts to HV DC bus. The internal HV DC bus is about 500 vdc and sets the maximum PV DC input for boost SCC converter. Battery charging takes HV DC down to battery voltage. AC input is converted to HV DC bus.

Vmp is typically 0.81 to 0.85 of Voc for silicon PV panels so with a 500 vdc max SCC that is about 405-425vdc max Vmp. When full PV power is not required the PV panel voltage will be allowed to rise greater than Vmp, up to Voc maximum which allows unneeded PV power to dissipate in PV panels.

The charge controller should self-limit its maximum PV input current, but that is not always the case for low cost AIO inverters. Over-paneling is having a greater maximum PV current than controller can take and letting PV controller manage itself for not taking more input current then it can handle. The over-paneling gives more current to SCC when there is lower illumination on PV panels.

 

[Ejimenez]

The 160 amps is battery line charging current and it depends on battery voltage. The maximum battery charging current is only at lower battery voltage.

From unit's weight specs, this is a HF inverter with a HV DC internal bus. All power is routed through this bus (with exception of AC input to AC output pass-through).

PV SCC is boost converter to HV DC bus. The internal HV DC bus is about 500 vdc and sets the maximum PV DC input for boost SCC converter. Battery charging takes HV DC down to battery voltage. AC input is converted to HV DC bus.

Vmp is typically 0.81 to 0.85 of Voc for silicon PV panels so with a 500 vdc max SCC that is about 405-425vdc max Vmp. When full PV power is not required the PV panel voltage will be allowed to rise greater than Vmp, up to Voc maximum which allows unneeded PV power to dissipate in PV panels.

The charge controller should self-limit its maximum PV input current, but that is not always the case for low cost AIO inverters. Over-paneling is having a greater maximum PV current than controller can take and letting PV controller manage itself for not taking more input current then it can handle. The over-paneling gives more current to SCC when there is lower illumination on PV panels.

View attachment 152839

So If I understand correctly, if the PV current is higher than the charge controllers max current input then the PV controller should adjust for that diference and lower PV current? (Panels have controllers inside of them to do this?)

I studied computer science with some electric engineering classes and man o man do electric engineers have my respects LOL, I can deal with physics, differential equations, programming languages and civil engineering stuff (I changed professions) but electric stuff? burns me out LOL

 

[RCinFLA]

(Panels have controllers inside of them to do this?)

The SCC controller does this.

 

[CharlesJacobs]

Panel specs are

Vmp: 34.9v
Imp: 13.19A
Voc: 41.8v
Isc: 13.92A



If im not mistaken inverter is rated for a MAX of 500VDC and MPPT voltage range of 90-450VDC, it says number of MPPT/Maximum Input Current is 1/27A.


im going for 18 of those panels so I am assuming I can make 2 9 panel series and then both series connect them parallel and thus would give me around (Using Voc) 376.2V and 26.38A which would work fine for the inverter specs right? (I assuming with cabling loss and temps of 80+(even 100F) would lower those values a bit more no? Do I need to consider isc with voc or its just voc with imp? If I use voc and isc for the calculation it would pass 27a easily. Would it be better to just upgrade the inverter to be safe? (im not doing this DIY but would like to be safe of what the installer/company is doing lol)

Voc (Open Circuit Voltage): 41.8V
This is the maximum voltage the panels can produce when there is no load connected.

Isc (Short Circuit Current): 13.92A
This is the maximum current the panels can produce when there is no load connected.