Absolutely mate, it's been a nightmare this year. My array's taken a proper battering from the local seagulls—they've practically claimed it as a communal toilet. Lost a solid 20% output last month until I got up there with the hose.
The thing that gets me is the timing. Winter's already brutal for solar generation with the low sun angle, and then you've got to factor in reduced output from accumulated grime. I've started keeping a squeegee and bucket of rainwater by the boat cabin—makes a quick clean-up easier than dragging the ladder out every other week.
What's worked for me is angling the panels slightly more than the manufacturers recommend. Water runs off faster, less pooling for debris to sit in. Though that's a conversation starter with the Victron monitoring system when your angles are all slightly off the standard.
I've heard some people swear by those wire mesh frameworks you position above the panels to deter birds, but they're pricey and create their own shading issues. Others suggest reflective tape, though I'm skeptical about whether it actually deters them long-term or if the birds just get used to it.
The shepherds hut's panels have been worse than the boat's, probably because the hut sits higher and more exposed. Thinking about installing a simple automated spray system for next winter—something low-cost that triggers after extended rain.
Have you tried anything beyond manual cleaning? Curious whether anyone's had success with bird netting or if it's just a winter ritual we've all got to accept living off-grid in the UK.