How great the risk would depend on quality of installation.
Typically the risk is rather low.
There should be no problem if the wiring is done right and the
PV units are tight and don’t leak.
Solar cells within the panels are protected by layers of glass. If the glass is broken and water enters into a working solar panel, lethal electrocution is a real risk.
Good selling point for us is many manufacturers void warranty if a pressure washer is used on these. We’ve had maintenance guys try this and damage them.
Avoid applying pressure or using high pressure to clean.
Do not attempt to clean a fogged or cracked panel.