Roof Lift Test
After wrestling with semi-flexible panels vs framed conventional ones, plus a myriad of ways to mount semi-flexible panels to avoid heat and vibration-related failure, it began to sink in that it was really going to boil down to a quasi-lifestyle choice.
I’ve been leaning heavily toward heaps of reliable electrical power with minimal inconvenience, which translates to using some some 600 watts-worth of lightweight solar panels on the Grandby’s roof. Find a campsite, raise the roof, and voila, you’re camping! What could be better? Then I found that semi-flexible panel technology is currently in a bit of a crisis because they do more than just lose efficiency in heat: they distort and fail. So they must be allowed access to cooler air, top and bottom. Vibration or regular flexing kills them as well. The common method of gluing them to the roof turns out to be the worst approach, and they can stretch and sag if suspended without support. Low points caused by distortion can hold rain run-off debris that creates hot spots or local overheating and damage, which is already much more likely in affordable-class panels using low-quality cells. They are not as durable in exposure as conventional panels, because they are faced in plastic instead of glass. Still, they are more efficient and compact, lighter, and can offer 600 watts on the Grandby. But it comes at a price: $1,200 for all six. The unsettling part, besides the need to juryrig a custom mounting system that these panels are not designed for, is that they have largely been withdrawn from the market. WindyNation is the only reputable low-end source I’m considering, and even then, they only offer them direct instead of via Amazon. With so much money at stake, that prompts one to think carefully.
Or, mount four rigid, framed panels for 400 watts of rooftop power, supplementing it later with an additional 200 watts of ground panels to be deployed when necessary. The attraction of this approach is that framed panels just work. There’s very little to go wrong with them, and they shrug off things like branch scrapes. In a basic 400-watt setup, I already have two monocrystalline panels, so two more would cost $270. Mounts add to that, plus any extensions of wiring. The downside of framed panels in this application is their weight at 17 pounds each, or 68 total. That’s a concern over time and miles, since the sometimes violent up and down movements created by dirt roads can warp a poorly-loaded 12-foot roof. Placing the panels near the corners of the Grandby’s roof should cut the stress considerably, since the lift struts attach there. The only remaining risk of damage is to me! Would I be able to reliably lift a roof with four panels permanently attached?
Once an appropriate time arrived to test the feasibility of this approach, I taped up the face side of each framed panel to protect the roof’s baked enamel paint, and heaved them both up onto the Grandby’s roof as shown in the first photo above. A few pieces of Gorilla tape to prevent sliding off during the tilt, and that was that. The recommended lift sequence of the Grandby is to push up the rear and then the front, which has less leverage. The rear was its usual no problem, but the front showed a decided new reluctance to rise. Since I’ve been slacking off on bench-pressing small European cars as a hobby, I found that putting my shoulder to the roof’s forward push-board got the job done in a repeatable way. That was a relief, to find out that a limited number of framed panels would be do-able rather than require a heroic effort. Adding the remaining two panels to the rear should make the front lift still tougher, but only a little bit. There will likely be room left at the roof’s center for a fifth framed panel, but I’d prefer to avoid that load without some field experience.
Adding two ground panels would up the ante, not just for the additional $270 panel cost, but for an additional solar controller. That’s the “Oh” part. I found that wiring roof and ground panels in one big series loop would be easy, since my existing MPPT controller can handle the combined 114 volts and 600 watts. But shading the roof while laying the ground panels in the sun collapses output from the entire panel grid. Why use series connections at all, then? In the case of Renogy 100W panels, the wires heading for the solar charge controller carry just over 5 amps at most, which allows the use of inexpensive 10AWG wire for most installations. (amps x volts = watts.) High voltage is no issue for wires, but high amperage is, requiring much thicker wire gauges and shorter runs of it. High voltage is a no-no for PWM (Pulse Width Modulated) controllers however, so a more expensive MPPT (Maximum Power Point Tracking) controller is required in order to convert the “excessive” array voltage into charging amps to the battery.
Sticking with purely parallel connections would work much better if I add ground panels to a roof system (so I could park in the cool shade), but also require tearing out the roof’s solar wiring to replace it with heavy cable and an upsized weatherproof connector. Not the best. With six panels total, the combined 600 watts comes through the solar wires at just 19 volts at best, which calculates to nearly 32 amps. That much amperage requires thick and expensive cable in very short runs. Otherwise, much of the panel output is lost to heat and big voltage drops before it ever sees the controller. Panel voltages and currents need to match, too.
At the moment, the wiring for the roof and ground ports join inside the Grandby’s cabinetry before leading to the battery. The smart way to go with ground panels here seems to be to alter the camper’s solar wiring to separate the roof from ground panel wiring, making two distinct wire pairs that each lead to their own controller, and then finally join at the battery. Thus if one set or other of the panels is taking a shade hit (or suffers a component failure), the system that’s still having sun doesn’t know and doesn’t care. It just marches resolutely on by itself. Since each subsystem is independent of the other, each can be wired with its own panels in series, in order to keep the wiring affordable and efficient, or in parallel, when an array is relatively weak.
The use of framed panels greatly simplifies screwless mounting. Here, the options range from extruded aluminum stands with Mary A’s suggestion of 3M VHB tape, to prefab aluminum or ABS mounts.
I found the Instapark mount above interesting, since it is almost as long as the panel is wide, and allows very easy external fastener access to remove the panel. Short and corner versions are also available. An extruded aluminum L-shape could do much the same thing, functionally. As with all adhesive mounts, the adhesion on your typical sheet aluminum roof may be compromised by the fact that the sheet rarely has full support underneath, or is generally not fastened in any way to what is underneath it. That may potentially allow the aluminum sheet to not allow full mounting pressure, or to point-stress the adhesive strip, particularly when the roof surface is very hot. I don’t see this as a likely practical issue in general use, particularly when the VHB tape contact area is generous.