Volkswagen was having issues a couple of years ago trying to keep
electronics alive, while shipping cars around the world, so they
ended up including a solar panel that plugs into a cigarette lighter
to keep the batteries topped off.
I don't know what others have for power requirements, but I use
my battery for instruments, and occasional inverter use with my
laptop. None of which puts a big dent in its capacitance.
The panels were available from the VW dealer for the asking or
you can get them on ebay for around $10-20 each - See Link at
Having installed two cigarette lighter plugs (one inside the nav
panel, and one facing the salon side of the interior) and both
set to the lighting circuit, I just leave the circuit in the on
position, making sure the lights themselves are off, and place
the panel in the slightly tinted fixed light with its four suction
cups. It remained charged all season. The cord reaches about 6'
so it can go to the area of the electrical panel. I just unplug
it while I sail. Have checked it over the summer, and every time
I return, my battery is topped off just fine.
It has a bridge rectifier built into the cigarette lighter plug
(so don't cut it off) in order to prevent battery drain at night
or during overcast days.
BTW, the cig. lighter adapters are
available at any auto parts place, including Wal-mart, for a couple
of bucks, and make handy 12V acc outlets. I installed, as I mentioned,
two and placed them on the lighting circuit. They even have their
own inline fuse. The panels are not weather proof, so it remains
inside out of the weather.
Note: This charger is only a TRICKLE CHARGER and
not meant to charge a dead battery, instead keeping a battery
topped up. The max power is a low 3.2w. with current a very low
170mA at max power.
- Larry Pockras