New ideas for solar panel installation

[Bill]

The forum is quiet these days, so maybe I can stir up some action with this.

When most of us think of adding solar panels to our camping rigs, we often think we must choose between mounting the panels on the roof of the trailer, or making them portable. This is a different approach. I think it has several nice features. Read on!

A month ago, my wife and I were settled into an ex-KOA in Van Horn, Texas, when the rig shown in the picture pulled in beside us. The truck, by the way, looks like a mini-truck in the photo, but was actually a full-size F-150 pickup with a cap over the bed. I immediately noticed the big wooden tray on the top of the truck, and the mysterious yellow wire leading to the trailer, so I had to talk to them about it. It turned out to be a solar panel array, of course, but in a mounting configuration that I had never seen.

They started off by telling us that they spend several months each year in Quartzsite, where they depend completely on solar power. But their small Casita trailer has no room for panels on the roof. Where to put the panels? Being mechanically capable, he built a shallow wooden box - a tray, really - that matches the size of the cap on the pickup. The tray rests on the cap’s roof rails, and is securely fastened to them. He removed most of the bottom of the tray, to cut weight and provide good air circulation below it. Then he built a second tray, just a bit smaller, that can drop inside the big tray. This second tray is built of aluminum angle stock, and it is also open on the bottom. The panels - 360 watts worth - are mounted to the inner tray. The cool thing - at least to my eye - is that the inner tray is secured to the outer tray using hinges with removable pins. By removing the appropriate pins, he can lift any one of the four sides of the inner tray up to a substantial angle (he said 30 degrees). This brings the panels up to the angle that best catches the sun. And since he can lift any of the four sides, he doesn’t have to point the truck in any particular direction.

The yellow cord runs from the solar panels to a set of four big golf-cart batteries on the A-frame of the Casita. The cord is short while they drive, so it doesn’t whip in the wind, and the batteries charge while on the road. In camp, the truck can be parked up to 50 feet away from the trailer, using an extension cord to bridge the gap. If they need to make a quick run into Quartzsite for groceries, for example, they can unplug the yellow cord, and take off in the truck with no worries about stolen panels.

With this approach, he has accomplished several things at the same time.
1. There is enough space for almost 400 watts of solar panels.
2. The panels are not shaded by the air conditioner, fans, etc. This maximizes solar capture.
3. The panels are easily tiltable in any direction, maximizing energy capture.
4. The system charges the batteries as they drive, something that portable panels can’t do.
5. The panels are out of sight and theft-proof - again, an advantage over portables.
6. He can easily disconnect and re-connect the panels when he wants to leave the campsite.
7. The panels themselves are protected from rocks and debris thrown up from the road. And by slipping a few blankets (or a sheet of foam board or plywood) into the outer tray, they are protected from hail.
8. The panels are securely mounted, without drilling holes in the roof of his rig.
9. The assembly does not increase the weight of the trailer (although the batteries certainly do!)
10. The cargo bed in the truck can still carry cargo. Since their Casita is small, this is important.
11. At the end of the camping season, he can lift the whole assembly off the cap, using a small hoist under the ceiling of his barn. No disassembly needed.

I like this. What do you all think?

Bill

[Larryjb]

I have two things I really like about the idea: 1) during winter storage the panels aren't exposed to the elements (tarped or not) and 2) it's not semi-permanently attached to the trailer making cleaning and raising shells easier. I may consider this when I delve into solar power.

[fairweatherfisherman]

Very interesting. Any guess as to how much that setup would weigh?

[klpauba]

That is awesome! Very clever.

[BrucePerens]

Panels with glass sandwich and aluminum frames weigh about 20 lbs per 100 watts. There is probably substantial weight added by the mounting scheme.

If you look at the cost of good panels, which is about $1/watt, it is in general better to add 20% more panels to a permanently flat system than it is to build a tilt mechanism. A 20% larger flat system would produce the same power for most of the day at continental U.S. latitudes compared to a system with one tilt angle set for the entire day. If you track the sun, you can beat the flat system close to sunrise and sunset, but at the cost of having the array raised to 90% at which time its wind load would be problematical.

The biggest problem is that panels handle shade poorly. Mine have three diode strings per panel, and if you happen to obscure a cell in all three strings, the panel stops conducting. I would like to have panels with a diode per cell rather than a string of cells per diode, that would probably work better.

[Bill]

As with most things, there are trades to be made. Bruce, as our resident skeptic, has pointed out a couple interesting ones involving the weight and cost of flat arrays vs tiltable arrays, and they need to be considered.

Trades:
At 20 pounds per 100 watts, if you add 20% more panels, you add 15 pounds of panels. Can you save 15 pounds by eliminating the inner (tiltable) tray and expanding the outer (fixed) tray? Maybe, but you won’t save much more than that. So this is pretty much an even trade.

At $1 per watt, if you add 20% more panels, you add $72 to the cost of the panels. Can you save $72 by eliminating the inner (tiltable) tray, and expanding the outer (fixed) tray? I doubt it, but you may come close.

In other words, from a weight and cost standpoint, flat vs tiltable it is pretty much an even trade for this configuration. But if your rig doesn’t have 20% extra area for additional panels, there is no trade to be made. The guy who built this thing made the trades that fit his needs and his rig, and others might make different choices. The point is that he has opened up some new ideas for all of us.

Bill

[Bill]

Originally Posted by fairweatherfisherman

Any guess as to how much that setup would weigh?

I wish I had asked the builder about weight - but I didn't. So here is how I would SWAG it.

Assume that the inner tray is 6 feet X 6 feet. That is 24 feet in circumference. If I build the inner tray using 1 x 1 x 1/8 aluminum right-angle stock, the aluminum angle weighs about 1/4 pound per linear foot, and 24 feet of angle stock weighs about 6 pounds.
Now double that number, to account for cross-braces, struts, nuts, bolts, etc. The finished inner tray is expected to weigh about 12 pounds.

Assume that the outer tray weighs about the same as the inner tray. Add maybe 5 pounds for the wood wrap. The total weight of the two trays is about 30 pounds.

Bruce tells us that the panels weigh about 20 pounds per 100 watts. The builder installed 360 watts of panels, so they weigh about 72 pounds.

Conclusion: Total weight for the entire thing is expected to be around 100 pounds.

Most of the weight is in the solar panels. They dominate the overall weight. The trays contribute relatively little.

You might choose to beef up the trays by increasing some of the pieces to 3/16" thick aluminum angle, or even 1 x 1 x 1/8 aluminum U-channel. They will be stronger, and the weight of the trays might increase from 25 pounds to 40 pounds. Quite reasonable.

Just my WAG, very loosey-goosey. Anyone want to suggest different numbers?

Bill

[Larryjb]

When I noticed the frame was made from wood, I immediately started thinking of different ways to build the frame.

3/4 PVC would be light, but perhaps too flexible. Perhaps filling PCV pipe with foam might suitably reduce the flex. I imagine you'd have to drill a number of holes and go through a few cans of low expanding foam for windows. However, if the frame is secured to the roof rack, this might provide enough support that additional structural support to reduce flex may be unnecessary. The PVC would be a nice conduit for wiring too. It would be easy to fabricate using T's and elbows.

An aluminum frame might work too. 1" square tubing similar to what's used on the TM might work fine. Unless you can weld aluminum, you might be faced with constantly re-securing the joints as they may come loose from vibrations. Also, metal so close to conducting electricity can be a recipe for shorts.

I'm sure there are lots of other concerns I haven't yet thought of. But hey, the got a man on the moon with a slide rule, I'm sure an lightweight solution can be found.

[Craigrrr]

I basically did the same, but with my suburban, I have 200 watts on the suburban and 1 panel on the TM, I can plug into the TM and parallel the panels for 300 watts total with a charge controller mounted in each the TM and the suburban. Seems to work great and I can run our Keurig coffee maker and induction cooktop as well using a 2000 watt pure sine wave inverter. I did this because our last trip to Missouri, we stopped every night and had to remove the bikes off the bike rack open up the TM hook up a generator etc... So I removed the second and third row seating in the suburban since it us only the two of us and dogs I made it into a sleeper aka Campurban, we can even just take the campurban out when we don't want to pull the tm and have a nice place to sleep. Even installed a 12 volt dc fridge in the campurban, so no more buying ice.

[klpauba]

Man, an induction cooktop? What kind of power does that pull?