For those of you who may be interested in a solar generator
this summer, here is a description of the system we put together last year. Similar pre-packaged solar
systems are available now from Costco and Harbor Freight, and they appear to be a great deal both from the perspective of cost and convenience in not having to track down all of the separate components. We put together our system before the packaged systems were available, and in hindsight I would have purchased the package rather than the separate components (cheaper and easier). Nevertheless, we thought it may be helpful to post the details of our system. The primary advantages of our system are that you can easily customize to meet your power needs, you can build it from other components that you may have on hand, and the system plugs directly into your 7-pole trailer receptacle (or that of your neighbor when they need a boost).
We assembled this lightweight, portable, and versatile solar
system to fully recharge the external 12V DC deep-cycle battery
on our 1984 Casita
16 ft. trailer. The charging system works well when dry camping
or when you just feel like capturing valuable energy free from the sun (see www.rvsolarelectric.com
). The charging system consists of the following components: two primary solar panels (18 watt each), one accessory solar panel
(10 watt), and a weather-proof field box that contains a 12V cigarette lighter input receptacle, a charge controller, a toggle switch, an analog voltage meter, and a standard 7-pole output vehicle receptacle.
The two primary solar panels are identical ICP Solar Battery-Saver SE (18 watt / $120 each at GI Joes) panels that are rated at a maximum rate of 1,200 mA at 15 V DC in full sunlight. These two 18 watt panels were joined together with a pair of 1” X ½” wood supports across the back, and they are mounted into a couple of steel brackets bolted into the bottom rung of a three-step aluminum ladder. A plug-and-play type cable connects the two panels at their base and raises their combined power level to 36 watts.
The mounting brackets consist of two Stanley “L” steel corner braces that were dipped in black “Rubberize-It” coating, and then bent at 90 degrees halfway along one of the “L” arms. The “L” brackets are affixed to the bottom ladder rung with ¼“ stainless bolts held by wing-nuts to allow for easy removal. We had to drill four holes in the bottom rung of the ladder to attach the mounting brackets. We have found it useful to bring this small lightweight ladder along during our camping trips not only to hold the solar panels, but also to step up to reach the top of the trailer vent, to reach the racks on top of our truck canopy, and to tie up a clothesline in a nearby tree.
The accessory solar panel
is a Solarex MSX10 (10 watt) panel that is rated at a maximum rate of 0.6 A at 17V DC in full sunlight. The mounting bracket for this accessory panel consists of a small photo tripod equipped with a bent aluminum “U” bracket. The combination of the tripod and “U” bracket allows the 10 watt panel to rotate freely and tilt into the sun. The cable from the accessory 10 watt panel plugs directly into the primary solar panels to yield a total solar power
generation system of 10W + 18W + 18W = 46 watts (3 amps). These solar panels can be easily moved around in the parking area during the day to remain in the direct sunlight and capture the greatest amount of solar energy.
Five more parts of the charging system are contained within a plastic weather-proof field box. First, we trimmed a ¼” thick white plastic cutting board to fit snugly inside the field box to serve as a base and to provide a raised surface that will let the wires run neatly underneath the switch and volt meter. Then we used a dremel tool to cut out holes in the side of the field box for the input and output receptacles. The cable from the solar panels ends in a male 12V connector that is plugged into a marine-grade female 12V DC receptacle that has a rubber cap to keep out water. The positive (white) and negative (black) wires run from the female 12V receptacle into the solar input terminals of a Morningstar SunSaver-6 charge controller (model SS-6-12V). The charge controller cost about $40.00, is rated at 6.5 amps and puts out a Pulsed Width Modulation (PWM) regulated charge of 14.4V (or 14.1V for a sealed battery). A green LED light
indicates that the solar panels are charging the trailer battery
. Black and white wires from the load terminals of the charge controller are routed through a hole in the white plastic base and into a lighted red automotive rocker switch ($4.00 from RadioShack), and then into an analog DC volt meter (model 22-410 / 0-15V DC from RadioShack $13.00). Finally, the positive and negative wires exit the battery
terminals from the SunSaver-6 charge controller and run out to a standard female 7-pole vehicle-side receptacle. The 7-pole electrical
plug from the trailer cable connects directly into the 7-pole receptacle in the field box and carries the regulated charge to replenish the deep-cycle battery. The field-box costs about $13 at Bi-Mart, and it has a lockable hinged lid and a rubberized gasket to keep out the rain, drizzle, and spiders.
During the summer, we used this solar charging system for a three night dry camping
trip on the northern Oregon coast. We found that the combined system generates somewhat less charging power than the calculated value of 3 amps, but the system does an adequate job of recharging our deep-cycle battery to keep up with our use of electricity. In the future, we plan to install a combination volt/amp meter inside our trailer so we can keep track of our electricity use and easily monitor the status of our trailer battery.
Special thanks to participants of the 2004 Oregon Gathering whose ideas helped create the inspiration for this project.