Going Solar

Joe M. Flake

I love to go camping, but not in a public campground. So when I bought my 1959 Shasta travel trailer, I decided that it must be electrically independent and able to roam beyond the limit of extension cords.

In the beginning my only electrical load was lighting, and this was easily accomplished. I obtained some 12 VDC tail light adapters that had Edison bases. I installed the adapters into the existing fixtures. I switched the wires from the ac input jack to a 12 VDC deep cycle RV battery. Going a step farther, I bought a trickle charge panel from Real Goods to keep my battery topped off. I was totally satisfied!

What Happened?

What happened was that I became intrigued with solar technology. Intrigued to the point that I started a solar business and took off to Colorado for an education at Solar Energy International (SEI). After that it was apparent to me that the Shasta travel trailer must be transformed into the Solar Chariot — able to boldly go where extension cords don't.

Sizing the System

Taking a load-dominated approach towards sizing the system meant getting real about my electrical needs and wants. My absolute camping needs were taken care of by the trickle charge system. But I wanted to have a rolling demonstrator for my business and a portable office/hotel/power station for remote installations. The decision was obvious. I wanted the largest system that the Shasta travel trailer would accommodate.

BIG IDEA — LITTLE SPACE

The Battery

I expected the system to be subjected to occasional heavy use with lots of time between uses for recovery. This meant that my battery bank should be disproportionately larger than my array. Extensive measurements revealed that the battery must be located under either the seat or the bed. Being concerned about electromagnetic fields in either location, I rationalized that there would be less electrical activity when in bed. So the battery went under the bed. The final choice was four 12 Volt Dynasty lead-acid, gel cell batteries (each 90 Ampere-hours at 12 VDC) wired in parallel to yield 360 Ampere-hours at 12 Volts DC.

The PV array

My array consists of two 60 Watt, Solarex MSX60 PV modules wired in parallel to provide 7 Amperes in peak sun. I thought that this was the minimum for my system, but the maximum for my budget. So far it has been adequate.

The Mount

I had two reasons for not putting the array on the camper's roof. I like to camp in the shade and I wanted the array where it would draw the most attention. A combination ground/truck mount suited both criteria. Camping on the north side of a tree with the array on the south side keeps me cool. Meanwhile the array and its umbilical cord attract curiosity seekers to the trailer. The mounting frame is made from channel aluminum with a steel tubing foundation. Hitch pins make for easy tilt angle adjustment. C-clamps are used to attach the mount to the truck. The umbilical is the 12/3 power supply cord that came with the camper. It is connected to the array and camper with polarized plugs for easy disconnect. The line voltage drop is less than 0.4%. If a stay is brief, instead of moving the mount to the ground I simply orient the truck and adjust the tilt angle.

Controls

For a charger controller I chose the Trace C30A; it allows for future expansion. It is wired to the old 120 vac input jack which is now the PV input jack. The circuit is protected with a 20 Ampere plug-in fuse. My inverter is the Pro Watt 1500 by Statpower. It has bar graphs for battery voltage and current along with overtemperature and overload indicators. The only thing I don't like about this inverter is that the lugs will only accommodate a #2 AWG cable with a rated ampacity of 115 Amps. Since a continuous load of 1500 watts at any battery voltage below 13 Volts draws more

Dynasty 90 A-h. 12 VDC Gel L-A Batteries

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