Power for the JATAC


“ . . . and nine—nine rings were given to the race of Men, who above all else . . . desire power.” J.R.R. Tolkein

In our case, a pair of 100-watt photovoltaic panels should be enough to give us all the power we desire. 

One of our major goals with the JATAC was self-sufficiency in terms of 12-volt DC and 120-volt AC electricity. We wanted to be able to spend a week or two—or more—in one spot and produce sufficient power to operate the fridge, water pump, LED interior lights, and our computers and camera-battery rechargers without the need to run the truck’s engine and alternator to recharge the camper’s batteries (idling results in very slow charge at best, besides using fuel, producing pollutants, and destroying the peace and quiet of your camp). A few minutes with an amperage chart led me to believe that about 125 watts of theoretical photovoltaic (PV) power generation should be enough to stay permanently ahead of all our consumption in reasonably sunny conditions, even with the fridge working hard.

Hyper-efficient LED interior lights use minimal power.

A few months ago, Walter Stoss and Urs Schoop of Global Solar—fortuitously based in Tucson—showed us their semi-rigid PV panels, designed to be cemented directly to the roof via a pressure-sensitive adhesive backing.  This eliminates drilling or through-holes, reduces the maximum wind profile to about an inch—essentially invisible aerodynamically—also reduces overhead clearance for branches and carports, etc., and renders the panels unnoticeable to passing potential thieves and makes the job of stealing them vastly more difficult anyway. 

The Global Solar panels utilize the most efficient Copper Indium Gallium DiSelenide (CIGS) thin-film technology, which maximizes gain at low sun angles and overcast conditions. Partial shading also has only minimal effect on the CIGS material (some types of PV panels shut down nearly completely if a branch or other object shades a small section).

We decided to err on the side of more power rather than less, and installed two GS PowerFLEX modules. Each of the 81.5 by 21.5-inch modules weighs about 22 pounds and is rated at 100 watts. The cylindrical MC4 connectors leading from the panels are themselves hooked to waterproof SAE fittings; thus the entire system required only two holes through the roof.

Waterproof SAE fittings connect the modules to the interior wiring.A Global Solar charge controller prevents overcharging, and eliminates the slight bleedback of power into the atmosphere that occurs at night with an uncontrolled PV panel. The controller’s display can read either voltage or incoming amperage, and can be selected for lead-acid or AGM batteries. Tom Hanagan at Four Wheel Campers recommended Exide AGM (Absorbed Glass Mat) batteries given his recent experiences, so, to ensure we had plenty of capacity to exploit the incoming amperage, we had him install two of the company’s group 24 batteries in the camper’s well-secured compartment. The charge controller mounted neatly above the camper’s other electrical panels.

So far we’ve subjected the system to a single easy test: a long weekend in the Dragoon Mountains east of Tucson (where Cochise and his Apaches made fools of the U.S. army in the 1860s). The weather was cool, which both maximized charge (PV panels work better in the cold) and reduced the load on the fridge. Nevertheless, by an hour after sunrise each day the charge controller was floating the batteries at a full 13.5 volts. Meanwhile, our friends Brian and Marisa, who’ve yet to install solar power on their Dodge/FWC combination, had to run their (VERY LOUD CUMMINS TURBODIESEL!) engine on the second day to top up their single camper battery. Just joshing, Brian.

Two Exide FPAGM-24DP batteries store power.

If we lived in town, I could literally hook this system up to the grid and sell power back to Tucson Electric. Instead, I’m considering adding an exterior plug and offering 12V power to fellow campers . . . for a small fee or a good beer.

Global Solar offers one- and two-panel RV kits, and many other solar products, here