Martin asked " So, flat on top of the boat may not be a bad thing in winter. Has anyone any actual data to confirm or refute this?"
I know that with a flat panel on Jannock's roof I have always had a charge indicator lit on the panel controller when I've visited the boat during winter daylight. What I haven't got is an ammeter in line so I have no idea how much charge is being produced. Possibly a project for next winter - install an ammeter. Graham www.jannock.org.uk
