Building a Solar Trailer, Part 1

by Ben N on August 1, 2021

Recently, I had a day or two available to work while waiting on things for other projects. For some time, I had the idea of a “Solar Trailer” in the back of my mind. I had seen a number of commercially-built solar trailers go up for auction, but at prices more than I could afford!
So, I wondered, could I build something similar for cheap using mostly components I already had?

I really liked the idea of a trailer where the solar panels would fold up for transport, then swivel out for use. I already had an old utility trailer and six used solar panels. Those are 250 watt panels which I got for about $40 each.

To start, I mocked up a cross-bar with a piece of PVC pipe I had. Both plastic and steel pipe come in ten foot sections standard. Three solar panels together comes to a total width just shy of that 10′, so the panels can be mounted to the pipe without needing to splice pipe together or cut it short!

I figured I would start with some 1.25″ black gas pipe. It’s a readily available material at any hardware or home improvement store. I’d need a way to connect the pipe to a frame which would mount to the panels. Pipe clamps seemed like the obvious way to do this. 1.5″ automotive exhaust clamps fit perfectly on 1.25″ gas pipe.

I laid out the panels (face-down) to figure out my layout. I purchased a few pieces of 3″ wide steel from the hardware store. That’s the widest I could find locally. The frames of the solar panels are 1.5″ wide, so the 3″ material fits perfectly across them. I placed the 3″ steel widths on the panels, with the pipe clamps on top of those, and then the gas pipe on top of that.

I marked all the locations for the materials. Unfortunately, the steel flat stock wasn’t long enough to reach the far outside mounting holes on the solar panels, so I would have to drill panels through the steel and through the aluminum frame. (I slid a block of wood between the panel and the frame, to prevent drilling all the way through and damaging the glass!)

After welding the clamps in place, I mounted everything together with stainless steel nuts and bolts. I also tried to “paint as I go” on many of the parts, hoping to not have to assemble/disassemble/reassemble too many times, and I didn’t want to accidentally get paint on the solar side of the panels either!

Next, was to design a rotating mount for the entire assembly. I got caps for the pipe, which would screw right onto the end. I drilled a 3/4″ hole right through the center of each, so that I could insert a 3/4″ grade-5 bolt. That bolt would then go through a 3/4″ bearing in a pillow block.

I tested this out by lifting the whole thing onto a pair of barstools, clamping them in place, and then testing the rotation. The concept seemed to work pretty well.

Next, I needed to create upright posts on the trailer to support the panels. I wanted something sturdier than I could find at the hardware store, but still inexpensive, and easy to obtain. I called up a friend of the family and asked to dig through her substantial scrap steel pile. In there, I was able to find some pieces of 1.5″ x 3″ c-channel. Each piece was a little longer than I would need, and there were enough pieces that I could find more when I came back.

I cut the c-channel to 36″ long and welded it vertical on the front corner of the trailer. There were plenty of existing points of steel for me to weld to, so the c-channel was rock-solid when complete. On top of the c-channel, I cut and welded a cap which the pillow bearing could sit on.

I measured out the distance of the 10′ piece of pipe to locate where I would mount the other upright. I was having trouble getting everything nice and even and square there. One thing I did was I ended up leveling the entire trailer. With it level, I could use a spirit level to make sure my upright was plumb, instead of only using a square. (Since this was an existing home-built trailer, there was NO expectation that everything was flush, plumb, level, and square!)

I welded the rear upright in place and then welded the cap on top of it. Now I was able to mount the gas pipe across the uprights. I had disassembled the panels from the pipe and brackets to paint them. WITHOUT the weight of the panels, it was easy to mount the pipe. After that, I installed the panels, one at a time, back on the pipe.

To keep the panels in a locked position, I had welded a plate to the pipe cap on the rear end. With holes in that, and a hole in a fixed point, I could run a pin through both to lock the panels up and down or at an angle.

With everything together, I was able to test the swivel mechanism while ON the trailer. It works well. The panels are still heavy enough that I need to make sure NOT to let go, but I CAN rotate them with one hand while installing the locking pin with the other.

My main concern was that on the rear mount, it wasn’t in a corner. Although it was very solid fore-to-aft, there wasn’t too much to prevent it from flexing side-to-side. This might me a lot of bounce and vibration while towing. I wanted to add some cross-bracing, but also make sure to still leave the rear of the trailer open so that I could load on and off of it. (For example, still be able to transport my electric lawn tractor!)
Here, I add some additional material for cross-bracing.

The master plan for the trailer is that it will have 6 solar panels on it. I want to make sure my mounting system is sturdy and works well before building the rack for the other 3 panels.
I’ll take the trailer to educational events and demonstrations. I also hope to be able to use it as a practical device for remote events – maybe even loan it to the local food truck so that they don’t have to constantly run a generator! Since I already have a grid-tie system at home, I’d like to have a grid-tie inverter so that I can continue to make additional useful power, even when the trailer is parked in my back yard.

I already have an inverter… of sorts. I still have the 2300 watt UPS which I used a while back for charging my electric motorcycle AND powering my house in a blackout. Check out the POOR MANS SMART GRID for more on that! I also already have a 48 volt battery pack kicking around. While it is rather small, it’s still perfect as a starting battery for this project.

Next, I’ll need to test towing the trailer. I want to make sure there aren’t any issues with vibration, tongue-weight, cross winds, or anything else I’m not thinking of.

Until then, stay charged-up!
-Ben Nelson

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