Believe it or not, one of the problems deserts have for growing plants is too much sun.
Or rather, too much sun for available water. Installing solar panels high enough that goats don't bump into them, and planting shade-tolerant arid plants, can absolutely support grazing.
Some grasses grow with partial light. With the right inter-panel spacing, could it be that a grazing animal might require more space, but not to an unreasonable degree? (I assume there are other considerations for the pasture...ease of finding the animals, moving them around, etc)
And while I'm thinking about it (and I'm way out of my depth here), but sunlight is a lot more powerful than growlights, is it not? Could power be siphoned to an extent, to supplement growth?
https://en.wikipedia.org/wiki/Agrivoltaic