GO SOLAR: Sun Power Installation Guide

Whether you're on or off the grid, solar power is a great add to your RV systems.

Photo Credit: photos and illustrations by Tim Walton

Whether you're on or off the grid, solar power is a great add to your RV systems.

Larry Walton
July 5, 2013
Filed under Trailer How To

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When we head out with our trailer, a good percentage of the time our destination is off the grid. We do some boondocking, but there are also the music festivals, hockey tournaments and other outings that aren’t out of town but are without hookups nonetheless.

Our Powerhouse generator is working great for us in most situations, but we also wanted to look into getting some free power from the sun. We were invited to check out a solar-system-install in Springfield, Oregon. Not only did we get to experience the install, we learned a lot about solar-system efficiency from AM Solar President Greg Holder.

 

 GETTING FIT

First of all, demand for RV solar varies with how RV owners use their vehicles. “I try to find out what it is they want to do and that helps me size the system,” says Holder. Some just want to maintain the batteries while the RV is in storage. This takes about 100 watts for a trailer and 200 watts for
a motorhome.

Next comes the conservative off-grid user. They use the light where they are sitting and turn it off when they move. They’re not running their microwave, toaster or blender. This type of user can power up with about 200 to 300 watts with 200 to 300 amp hours of battery capacity.

SolarIllustration

The more liberal consumers turn on more lights, watch TV, turn on a 2,000-watt inverter and operate the microwave. They will need 400 to 600 watts and corresponding battery capacity.

Next comes what Holder calls “hard-core boondockers.” They might be full-timers or have an office onboard and they consume a lot of power with additional uses, such as satellite Internet with their computers and TV. “Some of the bigger RVs have residential-style refrigerators that run on 120 volts AC, which means you don’t have the propane option, so you have to leave your inverter on 24 hours a day just to run the fridge,” says Holder. “These owners end up with 1,500 to 1,600 watts, whatever can fit on the roof.”

For those who want to fine tune their requirements, Holder suggests installing a shunt and an amp hour meter to record actual use. He also advises new solar users to install a large enough infrastructure in terms of wires, switches and controllers so the system can be expanded by adding more solar panels as needed.

Another way to ensure the best solar-powered perform-ance is to improve the efficiency with batteries, controls and wire gauge.

 

BETTER BATTERIES

Because an RV solar-panel system is really a battery charger, battery performance is a very important part of the equation. The better the batteries, the better the solar-panel system performs.

Typical flooded lead-acid batteries are the least ex-pen-sive but they have drawbacks. Absorbed glass mat (AGM) lead-acid batteries take advantage of purer lead, but they cost almost twice as much for the same amp hour capacity.

Improved battery performance means you can achieve your power goals with less solar-panel output, but Holder suggests “using up” existing batteries as you learn to use your sun-powered system. Such practice can damage expensive new batteries if charge levels drop too low.

 

GAUGE

A big part of wiring efficiency is achieved with AM Solar’s combiner box, which connects the 10-gauge wire from each solar panel at a bus bar that combines the panel power into a heavier-gauge wire to transmit the energy down to the charge controller. If wire gauges are too small or transmission distances are too long, voltage drop zaps a lot of energy from the system. Other wire characteristics that affect efficiency include solid or stranded, metal type and use of conduit. Prior to combiner boxes, panel wires were daisy chained together, which was both inefficient and destructive as the combined power could melt components.

 

TYPES OF SOLAR PANELS

Most RV solar panels are made with crystalline technology using silicone crystals. Cells are either multi-crystalline or monocrystalline. The monocrystalline panels are more efficient in low light conditions such as early morning or cloudy days. However, 90 percent of a day’s charge happens in two or three hours on either side of solar noon so multi-crystalline modules work well in normal conditions and are slightly less expensive. In addition to monocrystalline construction, efficiency can also be improved with a back contact design that eliminates the silver lattice work on the front that shades some of the panel.

Yet another efficiency gain comes from using “hotter” cells to make each panel. Cells are flash tested and grouped together by output quality so the exact same size module might come in 85, 90, 95 and 100 watts. The difference besides output? Price. More watts cost more money.

If the target output for an RV solar panel is 100 watts, improved efficiency really results in smaller, lighter panels. When roof space is at a premium, smaller panels can produce the power but at a price premium.

Other components can also contribute to the efficiency of the solar charging system and improve battery life. Battery temperature sensors, charge controls with pulse width modulation, and maximum power point tracking all contribute to “extracting the maximum power out of your solar panels and delivering it in a form that your batteries want,” says Holder.

Follow the guide below to see how to install a solar system!

Prep Panels

[1] Before heading to the travel trailer roof, the solar panels are prepped, which includes installation of the mounting brackets with adjustable feet.

Prep Panels (cont'd)

[2] The connectors that come with the solar panels are cut off and butt connectors are installed in preparation for taking the panels to the RV roof.

Mount Panels ...

[3] The exact location for each foot is marked before panels can be removed to prepare the roof surface area for installation.

Mount Panels ... (cont'd)

[4] At every location where a hole from a fastener or for a wire penetrates the roof, a clear primer must be used to prepare the roof for the sealer that makes the installation waterproof. The primer requires adequate ventilation and drying time before going on to the next step.

Mount Panels ... (cont'd)

[5] The elevation of each panel corner is adjusted by selecting different holes in the brackets. This design compensates for curves in the trailer roof. The goal is to get the panels as flat as possible. After fastening the brackets to the roof with screws, a liberal amount of self-leveling Dicor sealant is applied to each foot to make it weather tight. Sealant is also applied around the combiner box, cable ties/clamps and holes for wire routing.

Route Wires ...

[6] After mounting the panel, the AM Solar crew used butt connectors and heat shrink wrap to connect the double 10-gauge wires that transfer energy from each panel to the combiner box.

Route Wires ... (cont'd)

[7] Cable ties with built-in screw mounts are used to keep the wires in place on the trailer roof. A liberal amount of sealant is applied to each cable tie mount.

Route Wires ... (cont'd)

[8] The completed install from the top; two solar panels and the wire are the 
only visible components since the combiner box is mounted underneath one of the panels.

Route Wires ... (cont'd)

[9] Two priorities determine the wire routing: proximity and concealment. The floor-to-ceiling closet in the front bedroom of this Arctic Fox trailer was the perfect route between the solar panels on the roof and the charge controller in the front storage area. It’s best to use a long 3/16-inch drill bit from inside the cabinet face frame to go through the ceiling and roof to indicate the location for the 6-gauge wire from the solar panel combiner box to the charger control.

Route Wires ... (cont'd)

[10] Following the hole made from inside the closet, a hole saw is needed to make a pathway for the 6-gauge wires that go from the combiner box into the closet below. Another hole goes through the closet floor into the storage area that will house the control box.

Route Wires ... (cont'd)

[11] After routing the heavy gauge wire from the roof, through the closet and into the front pass-through storage area, it’s important to make sure there’s enough wire for a route that will keep the wires from being damaged by normal storage area use.

Install Combiner Box ...

[12] The 6-gauge wire that transmits energy from the combiner box to the control exits the bottom of the combiner box and goes through the opening that was drilled through the trailer roof.

Install Combiner Box ... (cont'd)

[13] The AM Solar combiner box features bus bars that can handle several wires of different gauges, has bulkhead openings for solar panel wires and offers excellent weather sealing. Dicor seals the box to the roof.

Install Monitor ...

[14] The back of the bedroom-mounted monitor reveals the battery sensor wires and a 4-conductor line cord, which goes to the charger control.

Install Monitor ... (cont'd)

[15] A small plastic basket works well as a vented cover to protect the monitor circuit board while split wire loom makes a clean and protected install for the wiring, which is routed through the closet.

Install Switch and Control ...

[16] A switch installed between the combiner box and the solar charge controller allows the trailer owner to turn off the solar power.

Install Switch and Control ... (cont'd)

[17] The wires from the monitor, combiner box and battery come together at the solar charge controller, which is the brain of the system.

Install Switch and Control ... (cont'd)

[18] A marine grade circuit breaker protects the circuit between the battery and solar charging system.

Install Batteries and Shunt ...

[19] The batteries were replaced in this trailer. High-performance batteries are a big part of a solar power system. Batteries that can efficiently take a charge and hold a charge make the whole system better and actually reduce the number of solar panels required.

Install Batteries and Shunt ... (cont'd)

[20] A shunt installed on the back of the front cross frame provides an accurate sensor for the system activity, which is transmitted via the two small wires to the monitor mounted in the master bedroom.

Install Batteries and Shunt ... (cont'd)

[21] IPN-ProRemote, Blue Sky Energy, is designed to monitor the system accurately, while calculating remaining battery capacity. It compensates for temperature, battery size, battery type and charge/discharge current. Past battery behavior is “learned” to continuously improve accuracy.

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