Once the Golf Cart Welder was working well, the next step was to add solar power.

Here's Marko welding a giant sports car rotisserie using the solar welder.

These panels charge the cart at about 3 amps. Welding or driving draws up to 150 amps, but only in short bursts.
To my surprise I have to disconnect the panel after a day or two to keep from overcharging the pack. I probably only charge one day a week. I better add an inverter so I can power my office and other tools from this thing.

Warning:
This thing is so damn cool you'll smile too much and hurt your face.
I probably should have put the cover back over the batteries before he started welding, cuz batteries can make hydrogen which can go pop.
You're smart kids, you can figure out other safety warnings for this thing.

Step 1: The Panels

A scrap dealer gave me a great deal on some badly weathered solar panels from the coast guard. He was on his way to his house in Zihuatanejo and was overloaded. Also he wanted to do us a favor. Thank you kind sir!

To my surprise most of the panels worked okay and the seagull poop cleaned off pretty well, althought the aluminum frames were pretty corroded.
These are 20 watt panels that produce an open-circuit voltage of about 18 volts. That's about right for a 12 volt battery, which is what they were made for. We wired up three of them to charge the 36 volt golf cart battery bank. Then I wired another three the same way to double the amperage. I tried them all in series, but it didn't work nearly as well. Only about half as many amps flowed.

Step 2: State-Of-Charge Indicator

This golfcart has flooded lead-acid batteries. If you overcharge them, the only problem is you'll have to add distilled water eventually. It's actually good to overcharge them from time to time. It mixes up the electrolyte and prevents stratification.
To make sure I didn't over-overcharge, I got a $3 alternator tester from harborfreight.
It has a series of LED indicator lights showing 5 ,12, 12.5,13,13.5, and 14 volts.
I wired that to two adjacent 6 volt batteries in the bank. When it gets over 13 volts I'll pull a cap on one of the cells. If I see bubbles I unplug the panel. Then I watch the battery voltage and when it gets down toward 12 I'll plug the panel in for a recharge.
Over-discharge is a lot worse for a flooded lead-acid battery than overcharge. That's what wrecks most car batteries.

Step 3: Panel Plug

This is the plug where the golf cart's old charger used to plug in. Now its where I plug the solar panels in. It spans the 36 volt pack. It's the same connector used on some computer battery backup systems. I scavenged one of those plugs to make plugging and unplugging the panel easier.

Step 4: In the Beginning...

Here's the original golf cart. It's an Ez-Go I got for free on craigslist. Notice the golf clubs.
It had four totally flat tires and six totally bulged and dried-up batteries.

One of the tires wouldn't hold air no matter what so I bought a new one for $40.
I should have just bought an innertube for it. Anyone know a good source for golfcart innertubes?

The differential plug was out and the diff was low on oil. I added some and made a new plug from a lobster buoy.

All the controls needed some lubing and working. I put my good batteries in it and drove it around on my cleanup errands til I was sure it was reliable.

Step 5: What Angle for the Panels?

Solar people know the proper angle for a panel.
If you can't move it you'll calculate the proper angle for your sun vs load curves and build your house with the roof facing that way.
We were planning to make a tilting roof that could be aimed at the sun, but when Franziska and I started taking off the old frame, it suddenly looked really good, so we bolted it back on looking all rakish like this, and decided to just point the vehicle at the sun. That made the rest of our job really easy. We attached the solar panel frames to this frame with hose clamps.

If you want independent angle control for your panels, this vehicle at makerfaire 2008 should be good inspiration.

Step 6: Panel Frames

We wanted the panels to be well supported and we hadn't devised the previous step's frame scheme ye., so we made some square tubing frames for them. These frames are probably a lot more solid than they need to be.
Here's Marc Lander at work cutting mitered corners with the cold saw. We welded up the frames with the homemade AC stick welder.
Then he marked the hole locations with a spring-loaded centerpunch, drilled 1/4' through holes with a hand drill, and cleaned up the corners with a flap disk on an angle grinder as seen in the next photos.

Step 7: Shock Mounts

To cushion the panels from road vibrations we made our own rubber standoffs. We cut chunks of rubber hose to slide over the 1/4"-20 mounting bolts.

Step 8: Painting

Don't just build something, paint it. Do it right away or it will rust and put rust marks on stuff.
Here's my mom painting a frame with shiny zinc paint. The frame is propped up on nail boards so we can flip it over and paint both sides without messing up the paint too much. You can also hang parts from wires, same intent.