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  • Writer's picturePacific Sun Technologies

Unplugged: RV Solar Systems

Harnessing the sun with solar panels keeps the power flowing when hookups are not available.

Even capturing a small portion of the energy of the sun is enough to provide electrical power for most appliances and accessories without the need to fire up the generator or plug into shorepower.

Did you know that an area the size of a 32-foot travel trailer’s roof receives enough energy from the sun during six hours in the middle of the day to power the typical American home for five days? It’s true. Studies show the energy from the sun shining on an area approximately 516 square feet is equivalent to 288 kilowatt hours (kWh) of electricity, and the average household uses about 30 kWh per day.

Hence the reason an ever-increasing number of RVers are looking skyward as a way to capitalize on the sun as a source of energy to supplement their existing dependency on shorepower and generators. New, more efficient technology helps further that desire to put solar power to work.

“Solar power is freedom. Freedom to camp wherever they want, regardless of if there are hookups or not,” says Garret Towne, president of AM Solar in Springfield, Oregon, one of the leading RV-oriented solar companies in the country. “We have customers in here every day having us install solar systems on everything from pickup campers and off-road tent trailers to goosenecks and fifth-wheels.”

Monocrystalline solar panels are a good choice for RV use. Standard mono panels show all the wire traces on the front. Back-contact mono panels (far right) have clean black squares and are slightly more efficient, and thus have a smaller footprint for the equivalent output.

“A lot of people have the misconception that using solar power is a political statement, which is trying to be ‘green’ or ‘environmentally friendly,’” says Towne. “And while that’s a nice benefit, installing a solar system really just comes down to having all the electrical comforts of home in your RV, using the most efficient, economical and silent way to do it.”

Taking that First Step

Getting to that point of having free­dom from always being connected to shorepower or cranking up a generator for hours at a time when boondocking requires taking a close look at one’s energy needs. The first step toward installing solar power is doing a power-consumption survey of your RV, and figuring out how much electricity is being used during a typical outing or over a period of time.

With that information, one can then decide on how best to build a system that accommodates those electrical needs — as well as possible future needs.

The Roof Puzzle When deciding on solar-panel array, get up on the roof and scope out the layout. Take cardboard cutouts the same size and shape as the solar panels you are contemplating. Leave at least 2 inches between the panel edges and any obstructions, and allow room to walk around when the panels are in position. Once templates are set, record the number of cutouts and their sizes to make it easy when price shopping.

The most accurate and easiest method to measure daily power consumption is employing a kilowatt meter for the 120-volt AC appliances and accessories, and a battery monitor to record the DC loads. Kilowatt meters come in a variety of types, including inexpensive ones that monitor the kilowatt hours of whatever appliance is plugged into the device. They are readily available on Amazon and through some of the sources listed on page 43. Smart battery monitors, like the one from Thornwave Labs, will transmit your battery-usage data to a smartphone, and are particularly useful with lithium batteries that have a nominal change in voltage across the discharge cycle.

If you don’t have a kilowatt meter or want to invest in one, you can go the old-fashioned route: call a solar RV expert (again, see our source list) or figure it out yourself. Take the watts rating listed on each appliance/accessory you use and divide that by 120 (volts) to get the load in amps. Then do the math to determine the usage in 12-volt DC amp-hours (Ah) for any given day. For example, a single-cup coffeemaker powered by an inverter might be rated at 1,420 watts, so dividing by 120 (volts) equals about 11.8 amps. If the coffeemaker is used only 20 minutes a day, that would equate to about 4 Ah per day.

A typical RV refrigerator running on LP-gas uses about 19 Ah per day to operate the 12-volt DC electronics, while a 40-inch LED TV that is rated at 150 watts and watched four hours a day consumes 5 Ah. Be sure to include items such as the water pump, stereo, lights and fans, and power to operate the inverter and even chargers for phones, tablets and laptops. Anything that consumes electricity needs to be in the tally. This will give the numbers you need to build an adequate battery bank and solar array. Keep in mind that AC loads powered by an inverter need to be multiplied by a factor of 10 to determine the current in 12-volt DC.

Batteries: The Heart of the System

There are three types of batteries used in RV solar systems: flooded, absorbed glass mat (AGM) and lithium. Flooded batteries have wet cells, which have to be maintained with distilled water on a regular basis. AGM batteries are sealed, and unlike flooded-cell counterparts, do not gas, which makes them safer to use in unventilated environments. Of the two, AGMs are better because they are able to withstand more charge/discharge cycles and generally have a longer lifespan than wet-cell batteries.

Selecting the proper batteries for the battery bank is the key to the entire solar-charging system. Either flooded, AGM or lithium-iron-phosphate batteries can be used, with the latter the most efficient. Here, AM Solar installed two Lifeline 300-Ah AGM batteries to store the power from three 100-watt solar panels.

Lithium batteries are the best. They are considerably more expensive than the best AGMs. The upside is lithium batteries last up to three times as long as AGMs and their output level stays constant through the entire discharge cycle, whereas AGM and flooded batteries begin falling off even before they are at 50 percent charge. If money isn’t a deciding factor, go lithium. Keep in mind that several peripheral electronic devices might be needed in addition to the cost of the batteries themselves.