[schiffern]

>spraying the panels with water every half hour

Sounds like a job for center-pivot irrigation! Just choose a model that can rotate at 2 revolutions per hour.

I never really appreciated how brilliant these are until watching this video:

https://youtu.be/7j1lMs7fcIQ

For large deployments of Earth-mounted PV you'll need a grid of drainage ponds to buffer runoff water, so you might draw from those. A control system would monitor temperature, PV output, and water turbidity.

The latter is important, since there's no sense dumping dirty water on the panels! Give the suspended solids time to settle out, or even add flocculants via a dispenser.