Solar - Point of Common Coupling

It's probably important to get the interpretation of a PCC correct to start with.

Prior to the advent of high volume small scale co-generation, the PCC was located at the utility transformer as that was the main point of distribution for the local community.

As more and more small scale grid tie Pv systems come on line, the one PCC has become many and moved to be where the utility service and each Pv system come together. This is generally at or very close to the inverter.

I am assuming here that the transformer to which you refer is the utility transformer outputting to consumers and also receiving power from Pv systems as there would unlikely be any pf induced voltage sag between an inverter and a dedicated transformer feeding into a utility grid from a large scale Pv array

The drop in voltage is caused by the Pv system injecting power back into the grid at unity pf - active power only, this has the effect of reducing active power in the utility but leaving apparent power unchanged. The ratio of apparent power (normally lagging) to active power thus increases, pf falls further below unity, causing the voltage on the grid to sag.

The generators must then produce more apparent power to rebuild the voltage thereby further exacerbating the pf deficiency.

This problem would be largely overcome with the simple addition of leading pf correction in the grid tie inverters. They would then inject both active and leading reactive power into the grid, thus alleviating the voltage sag dilemma.

This correction could be done at the transformer but would be on a much larger and very much more expensive scale than if done locally at the inverters.

Due to the high variability in output from PV systems, a pf correction system at the transformer would need to be constantly switching capacitor banks in and out of circuit to keep the pf on target. Localised pf correction at the inverters is far easier to control.

The question becomes - Who pays? - those supplying the power should ensure that it is of a suitable quality - in this case that is the co- generator rather than the utility.