From some of the comments made above about semi-flexible solar panels like the ones pictured in my last post, one might think that after three years, a bit of clouding, scratched surfaces and a sprinkling of guano, semi-flexible solar panels might be completely useless.
I'm happy to report that this is not the case.
No scientific multi-meter measurements to back up this proposition but after a few weeks with the panel and bimini removed in a desperate attempt to find some late season speed in our twilight racing (during which the frig being on is mandatory - as any self-respecting twilighter will attest), I discovered that the house batteries were down to about 11v and in urgent need of a top-up.
So I reinstalled the bimini, cloudy solar cells and guano included, and plugged the wires back in. Two days on the mooring - hey presto! Service batteries back up to full charge.
I am sure that shiny new ones would be even better but I see no need to splurge on any replacements for a while yet.