Reverse breakdown voltage setting for the diodes in a solar cell model in SPICE
From LTWiki:

There are two types of diodes available. One is a conduction region-wise linear model that yields a computationally light weight representation of an idealized diode.
...
This idealized model is used if any of Ron, Roff, Vfwd, Vrev or Rrev is specified in the model.

So when you included the VREV parameter, you changed your model to use the piecewise linear diode model instead of the usual nonlinear model. Your other parameters (IS, XTI, and BV) are ignored and the piecewise linear model parameters that you didn't specify take their default values.. This could make a substantial change to the operating behavior of the diodes in your model.