Haven't read the full article (paywall), but the biggest issue with co-mingling livestock and solar panels is the damage they cause to the installation by chewing through or rubbing up against insulated wires.

Also, when the panels are at full extent first thing in the morning (e.g. almost vertical facing east), it's very easy for animals to come in contact with the panels themselves.

The corollary to this (at least in Australia) is that most solar farms are being installed on (now) vacant grazing land where 150+ years of cultivation has meant that the grasses that grow on them are very fast growing and hardy.

Mowing the fields beneath the panels is a full time job just to reduce the fire hazard.

...and sheep are good for preventing forests from regrowing in the UK and the Republic of Ireland? (for one regional example)

And sure, wool and mutton too, but the level of environmental destruction wrought by humans via sheep is baaaad.