Two years ago we added solar to our then 18-year old Roadtrek 190 Popular. We followed the rule of thumb you often hear, “Add 100 watts of solar for every 100-amp hours of battery.” We had one 80-amp hour battery. After much research and a lengthy discussion with the vendor on requirements we bought an entire system from AM Solar for $695 and installed it ourselves (click here for the story).
Two years down the road we revisited the subject. Should we change anything? Should we have done anything different? In retrospect we would have gone with a different controller than our Morningstar SunSaver 15 MPPT (which AM Solar no longer sells), but both of the controllers we would choose today were not available back then. We eventually added a solar cut-off switch because we managed to “boil” our poor battery big time by leaving the camper plugged into shore power after the snow on the roof melted. The solar system woke up each morning and went into bulk charge for 3 hours on our already fully charged battery. About an inch of plates were exposed in each battery cell by the time we realized what was happening. Now we turn off the solar when we plug into shore power or go on long drives. After nursing that battery for a year, we finally spent the $79 for a new deep cycle group 24 battery! We shouldn't have waited so long.
The 100-watt system worked great for boondocking – as long as we had sunny days. With sun the battery would be recharged by 1 p.m. And we had no trouble keeping up with typical daytime loads. But without sun, the story was different. Sure the solar panel put out a little juice on those rainy days, but it wasn't enough to keep up with the daytime power use, let alone recharge the battery for the coming night. We would have to run the Onan generator for longer than we really wanted to! We figured our typical daily use at about 35-amp hours, which is lower than most users, but with an 80-amp hour battery we had to recharge every day. No coasting through several rainy days! By the way, before you add solar, install a battery monitor and learn what your daily usage really is! Estimating is unreliable. Here is how to install a Trimetric battery monitor (click here).
We discussed the possibilities – adding more battery or adding more solar or both. A possible game changer was Roadtrek's announcement: Their NEW engineered lithium-ion power modules come in 200-, 400-, 800-, 1,600-amp hour versions. And unlike wet cells or AGM batteries that should only be discharged to about 50 percent, lithium-ion batteries can be discharged to more than 80 percent. That would be 160 ah, 320 ah, etc. of usable power. With our 80 ah battery we had 40 ah of usable power. We had dreamed of a 300 ah (a usable 150 ah) as our ideal system.
One of those new EcoTrek 200 modules would provide 160ah at about the same weight as our current battery. Alas that was not meant to be. Roadtrek is NOT doing retrofits. Plus the major upgrades to all the wiring from the alternator, to the converter and the addition of a new charger capable of putting out the power lithium-ion banks need for charging are so extensive that it really does not make sense for older Roadtreks. We had hoped lithium-ion batteries might charge slower on lower wattage chargers meant for conventional batteries (after all we were more interested in total capacity than speed of charging), but not so. You need not just the fancy battery control system but a NEW charging system. However, for those wanting to buy new, this is truly exciting technology!
Back to our needs: We concluded (again) that adding more battery did not make sense. We had no space to put new batteries. And weight was also an issue. We measured carefully to see if our battery compartment could be enlarged a bit to hold a Group 27 battery. We concluded it would be difficult if not impossible. Although AGM (sealed lead acid) batteries did not require a vented compartment, they offered less amp hours for the same size factor and often 2-3x the cost. And all lead acid batteries are heavy. If we screw up (again) and fry a $79 wet cell, it is not a big deal. But ruining a few expensive AGMs is a big deal.
The infrastructure needed for lithium-ion really takes them out of the running, but perhaps in the next few years, some of the newer battery technologies will become practical for retrofit. Additionally, we discussed an inverter to run a microwave and Keurig (the only things besides the air conditioner in our Roadtrek that are not 12-volt). Again we concluded it wasn't worth it and really didn't make sense without a battery upgrade. Plus, the Onan needs to run to keep it in good working condition, so the microwave and Keurig are good exercises for the Onan.
More solar made the cut. The few times a year that we boondock for more than an overnight or two, the solar was wonderful – as long as it was sunny. But it wasn't always sunny. So we talked to AM Solar (we were very happy with their advice, customer support, and service the first time) and bought a second 100-watt panel identical to the first one. We also chose to add a combiner box to make it easy should we someday want to add more. As before, the stuff arrived carefully packaged and with detailed instructions. AM Solar also has some good videos on the installation process. We had centered the previous panel lengthwise on the roof behind the Fantastic fan. We elected to run the two panels crosswise. Actually we were about 3 inches short of being able to fit three panels. There is room for one forward of the Fantastic fan should we someday wish for 300 watts (not likely with an 80 ah battery).
We installed it – about six hours of our time. We left the next day for a week unplugged. The weather was extremely hot (90-99 degrees Fahrenheit max) and mostly sunny. Running the Fantastic Fan on 2 or 3 all night, plus the Sirocco fan(s) on 3, plus our new fridge fans would leave our battery at about 73 percent in the morning. But the 200 watts of solar had our house battery fully charged by noon. It kept up with the daytime fan use as well.
As one solar sage said “you can never have too much solar.” Especially when it isn't sunny! Our advice – go for at least 200 watts of solar. More if you have room for it. Do not feel limited to 100 watts of solar for every 100 amp hours of battery.