Isc is it critical to consider in all in one off grid system? Fry or Bye bye

[Solar. Enthusiast]

I have been searching but couldn't find a clear statement about it. i noticed that All in one inverters with higher voltage MPPT 500V have lower Max PV input current approx 18A.
However Isc of solar panels rated as 450W and more are usually around 10A. thus paralleling in this case will lead to high PV input current 20A.

Some people say that the inverter will limit the extra PV input current which leads to loss of power and others say introducing high PV input will Fry your inverter.

Anyone with some decent info to solve this dilemma is welcomed.

 

[Samsonite801]

Try to think of it in this way. Amps is 'drawn' up by the charge controller by variating the resistance on the PV circuit. If it sets high resistance on the PV circuit, the PV voltage will stay up high. When it is sweeping the MPPT to find maximum power point, it will gradually lower the resistance on the circuit, which 'pulls' down the voltage and increases the amps, until it pulls the maximum current that it can until it hits its max amp rating (which may be well under Isc max possibility of the PV circuit).

A good quality charge controller wouldn't be able to draw more amps than it can handle. Victron for example, you can see they have a footnote in their spec sheet for the 250|100 (a model I own), which says:

"1a) If more PV power is connected, the controller will limit input power." (see picture)

Generally speaking, over-paneling should be fine to do, as the charge controller will not pull down the voltage enough to draw more than it's highest amp rating. Obviously, this may not be a blanket statement for all brands. Victron allows it. The biggest number you can't go over though is on Voc.

But I might send a letter to the brand manufacturer and ask them if you can over panel on Isc with their CC safely. Victrons can over-panel, they just won't allow to pull more amps than their max, so it will just be wasted watts (good for dark cloudy days though).

There are multiple other threads here talking about over-paneling ( https://diysolarforum.com/search/614232/?q=overpaneling&o=relevance ). I would think any decent CC would not have a problem, and would simply not be able to load the circuit (pulling down the voltage enough), to go beyond its max rated amps.

Some people have even used charge controller (like the Midnite Classic 250), with a battery connected to supply the PV side), like on the Prius hybrids for example, and the Midnite Classic will only pull up to max amps rating off the battery (connected on the PV side). They had used a charge controller as a workaround to use a 210 VDC Prius hybrid battery to charge a home 48v battery bank, with good success. The charge controller would only load down the circuit sufficient enough to reach its max amps rating.

 

[Ampster]

Anyone with some decent info to solve this dilemma is welcomed.

I am not sure it is a dilemma that needs solving. Most All in One's use high voltage strings presumably because it is more efficient to convert to 240 volts. Charge controllers only have to charge typical 48 volt batteries and not be concerned with converting DC to AC.

 

[robby]

The Voc is what you really need to watch the most.
A company down the road from me burned out two SMA 3 Phase 25KW Inverters just by adding a couple of extra panels to the end of the string. BTW warranty is void under that condition.

 

[fafrd]

I have been searching but couldn't find a clear statement about it. i noticed that All in one inverters with higher voltage MPPT 500V have lower Max PV input current approx 18A.
However Isc of solar panels rated as 450W and more are usually around 10A. thus paralleling in this case will lead to high PV input current 20A.

Some people say that the inverter will limit the extra PV input current which leads to loss of power and others say introducing high PV input will Fry your inverter.

Anyone with some decent info to solve this dilemma is welcomed.

MPPTs do a pretty fantastic job throttling back power (current) when no more available power in needed.

So I’m general, you don’t need to worry about Isc exceeding your MPPTs max input current rating.

The one exception to that is if you have an shading on your array.

If there is shading which lowers power below MPPT max levels, the MPPT will reduce string voltage and eventually bypass diodes will be activated to increase current back to ~Imp.

Since string Voltage is lower (~2/3Vmp or ~1/3Vmp), power can be well under max levels and the SCC may be exposed to input current of ~Imp.