Off-grid solar: plans and lessons…and plans…

imageFrom the very start of the #trailerlife project, I was motivated by the principles of sustainability (using less) and independence (being off the grid). Partly I set these goals as an interesting experiment, and partly as a practical attribute in case I want to move the Spartan someplace remote in the future. Sustainability and independence are not inextricably linked, but they do work nicely together. The former dictates small and less, which makes the latter a more realistic goal. Do less with less.

Early research online and conversations with the knowledgable folks at AMsolar in Oregon (experts in RV solar applications), and locally with Ryan Wallace of Qwiksolar, who also has considerable off-grid experience, convinced me that meeting my electric needs by gathering photons from the sun and converting them to electricity was not only feasible but affordable. 30% tax credits didn’t hurt either.

The concept underylling off-grid solar power is straightforward: solar panels collect sunlight and convert it into electricity, which is then stored in a bank of batteries, which powers whatever is hooked up to it.


Ryan suggested I write up a list of devices and appliances and their loads to help us determine the wattage of the solar panels (how much energy I would need to borrow from the sun) and the amp-hours of the battery bank (how long I could store that energy until I used it).

Knowing that I was limited by space and money, I had to seriously think about my electricity use. An ipad or computer could suffice instead of a TV. This was easy since I have not owned a TV for almost a decade. The electric teapot would have to go, sucking a staggering 1500 watts. While the ipad could stand in for a radio, I didn’t really want to part with my 1950s zenith tube radio. And I needed to be able to run my sewing machine, to which future posts will attest. A picture of my off-grid solar use began to emerge.

Solar panels are natively direct current, or DC. Campers, like cars, have DC electric systems to run thier lights and electronics. (DC electric powers that car cigarette lighter that is more likely to charge a smart phone these days than ignite the business end of a Virginia Slim.) The batteries used for storing electricity collected by solar panels are also DC.

To run normal household appliances that run on 120 volt alternating current (AC), like my beloved Pfaff 360 sewing machine, the 12 volt DC electricity needs to be inverted to 120 AC. The device that does this is called, plainly enough, an inverter.

The inverter loses energy in the process of changing DC to AC, which makes it more efficient to run as much as much possible on 12 volt DC. The cabin lights, ceiling vents, range hood, propane furnace and refrigerator in the Spartan all run directly off the DC system. The inverter, once hooked up, will feed 120AC to the three power outlets in the trailer, which will run the occasional applicance like the sewing machine (and ipad, which seems to charge bettery on AC than on DC).

Ryan suggested I start with at least 450 amp-hours of batteries (4 Trojan T105s at 225 amp hours each–they are six volt so they are paired in series and then the pairs are joined in parallel, hence 450 amp-hours at 12V) and 900 watts of solar panels. “I have never heard anyone complain that their off-grid systems are too big,” Ryan said.

We installed the batteries in the back storage bed:


After the batteries were in, we installed a TriStar Solar Charge Controller next to the existing converter and 12V fuse panel:


We opted not to install the panels onto the roof of the trailer because of time constraints, and because Ryan hapened to have four 225-watt panels mounted on pallets that we could press into service:


The phase one solar system was up and running, and it has by and large met my needs, which are minimal at this point. Earlier this winter, when a long streak of cloudy days struck, I had to charge the batteries from the grid, using a long extension cord and a powerful automotive battery charger. They have been independent since then, and even though this winter has been, well, wintry, the short days and even shorter breaks in the clouds have provided enough power to survive.

Still, it was clear that phase two needed to happen. I really want 120V AC power, but I have been leery to add the inverter until I expand the battery bank. I also recently installed a small propane furnace (hooked up to a 80 gallon/300 pound propane tank) to help with the heating and it draws a small but not insignificant amount of electricity from the system. And I also just ordered 39 yards of olive green water resistant canvas with the idea of sewing up a skirt to go around the trailer and seal off the underside from the constant cooling action of even the slightest breeze; I need to plug in that sewing machine!

So the other night I sat down and began to sketch out what the phase two system would look like, using the inverter manual as a guide. The idea is to double the battery bank and install the inverter to get 120AC online:


It’s not a terribly complex system, or at least, it isn’t once you sit down and draw it out. Stay tuned for a follow up post on the phase two installation!








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