The short answer is that it is usually insignificant.
On the DC side, this is the short circuit current (Isc). The limiting case on the I-V curve, where V=0. You would add the 125% enhancement factor to account for irradiance exceeding standard test conditions.
On the AC side, look for the term "maximum fault contribution current" if this information is available in the inverter product documentation. It is common for utilities to ask for this information on the applications, because a source with rotating machinery has significantly higher fault currents than its operating current. For other kinds of sources like generators, you could expect this to be tens or even hundreds of times the full load amps of the source. This is not the case with inverters, and the maximum fault contribution current might even be as low as the inverter's own full load amps.