I put a single 80w panel on the wheelhouse roof of my 331, SKYLER about 3 years ago but was not very impressed by the output – never more than about 2amps on my remote meter – but enough to keep the batteries fully charged despite the drain caused by the bilge pump when the boat was left for a week or two. But after a couple of years the panel failed altogether so I complained to the supplier. He supplied me with another 80w panel (at a discount) but of a later design. This one was much more efficacious – it would regularly charge at 4 amps in sunlight – more than enough to run the fridge when we were at anchor. I have now sold the boat so cannot say how well it continues to perform but I do think that the technology has much improved in the last year or two.