I have a pair of 18 watt panels on my sailboat. The panels connect to the boat's system via charge controller. They put out about 15v, so on a sunny day put out about 2.4amps. Just perfect for trickle charging.

Our sailboat engine usage is that on a sailing day, engine gets started, runs for about 20min getting out of harbor, then gets shut off. At end of day engine gets started and runs again, maybe for 10 min. Rest of time just sits at dock with small loads like bilge pump, radio memory, pilot lights etc. After 2 weeks or so like that, the engine wouldn't turn over. With panels installed (about 3 years), batteries are always fully charged. (We have one 12V starting battery and 2x6V house batteries connected)

This one by Coleman might work for the tractor (I am sure you can find same thing in USA!):

Coleman 40W Folding Solar Panel | Canadian Tire

Thanks, looks like the size and cost I first hoped for are not realistic...
I was thinking of something I could attach to the roll bar and leave in place...
May have to wait until technology makes further advances....

Mine attaches to the battery via regular clips. I set the solar part on deck and leave. It hasn't blown away. You could leave it connected on the hood or windshield if humans aren't likely to come along and grab it.

Yes, if you go to harbor freight you will find that the little Solar Battery Maint Chargers charge in miliamps.

I use the 15watt panel from harbor freight.

it keeps the battery in my TD up just great. it's only 1 amp... so not enough to boil out a battery.

I have a 20watt amorphous cell on my car hauler dual battery rig. I got it from Northern tool.

my garage has 3 45watt sets connected to a battery bank to keep the deep cells charged, and I have a long cord I connect to the tractor when it's parked, as I STUPIDLY connected the battery cables backwards, and melted the alternator... and it's some tiny alt I can't find anywhere. I'll likely have to get it rebuilt at an alternator shop.

Tagged to watch. Would like something for my GTO. Lots of parasitic load and driven infrequently, especially in the winter.

I've been eyeing this one:
BatteryMINDer 12 Volt Solar Charging System with 5 Watt Panel and Desulfator, Model# SCC005 | Battery Maintainers| Northern Tool + Equipment

It costs a little more but I've really been happy with their plug-in version. It also handles two batteries so I can connect riding mowers as well.

You park your GTO outside? What year?

The '04 in my signature. Nothing cherry or special, although it's got some go-fast goodies under the hood.

Like most red-blooded Americans, I park my expensive cars outside and keep a bunch of worthless junk in the garage.

LOL

VW solar panels
 

VW shipped a lot of cars over the years with a small pv panel to keep the battery charged. It comes ready to plug into the obd2 port complete with suction cups to mount it under the windshield. Lots of 'em on ebay.
Small pv panels (< 30 watt) rarely need a charge controller when connected to a battery because they do not put out enough power to cause electrolyte loss.

I have not been able to find the obd2 port or the windshield on my 1978 5600 Ford tractor... but I will keep looking.... LOL
My 1980 240d does have a windshield...

Lol... imagine that.:P

Odd, my 1978 cub cadet has a cigarette lighter port on it... I'm not sure why VW would connect it to a USB port?

Cub Cadets are advanced designs...
I wish my JD mower had that since my portable air compressor would plug into that..