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Switzerland authorizes removable PV plant on railway track
(www.pv-magazine.com)
This is a most excellent place for technology news and articles.
Standing next to trains as they pass, or on one's with open decks, you'll know they produce a lot of wind. I assume under the train this is even stronger, with a strong low pressure area. This should be able to clear most obstructions without an issue whenever a train passes. Sure, it'll also toss more on, but there's some equilibrium that it'll reach and it shouldn't ever get worse. My guess is that's well before it is a major issue for the panels.