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Solar Panel Installation Tips
Solar panels aren't the hardest thing in the world to install but there are a few tips and hints that can make your job that much easier. Once you have the system designed and your solar panels, panel mounting brackets, and charge controller are all picked out all you need is few basic items to finish the installation.
Mounting the Panels:
Regardless of whether you decide to use the popular flat mount Z brackets or the adjustable flip-up brackets you will still have to fasten the brackets to the roof. Solar panels are perfect for mounting on a fiberglass RV roof. The panels themselves attach to the aluminum Z brackets with bolts. Because these panels can vibrate when traveling down the road the nuts do have the potential to loosen up over time. For this reason it's advisable to use nylon lock nuts to prevent this from happening. Also, use the larger USS series of flat washers rather than the smaller SAE series of flat washers. This will give you good clamping area on the aluminum brackets and minimize any stress cracking by spreading the force out over a larger area.
The next step is to mount the brackets to the fiberglass roof. Fiberglass is all that thick and installing screws into the roof isn't the best choice because the fiberglass material is relatively soft and the threads may pull out so that the screws aren't holding anything. On a thicker rubber over plywood roof screws may work fine but they just aren't that great on thinner materials. In this case a pop rivet is a better choice. The advantage to a rivet is that the back side of the rivet expands when compressed in the riveting tool. This forms a "knob" on the backside of the material which has much better holding power than a threaded fastener in this situation. Be sure to use 3/16" diameter stainless steel rivets with stainless mandrels. Because the mandrel will remain in the hole you don't want a steel mandrel which could rust. When you are all done by sure to use plenty of self-leveling RV caulking both underneath the brackets and over the top of the finished rivet heads.
Running the Wire:
When purchasing wire you need to decide how large of a wire gauge you will need and what type of wire you will use. Take your total solar array wattage and divide by 10 volts. This will give you the maximum amperage that will be carried on your wiring. For example - two 120 watt panels could pass a current of 24 amps. Four panels could pass a current flow of 48 amps.
Charge Controllers generally come in 30 amp and 50 amp models. Be sure to allow for any future expansion when planning both your wire gauge size and which charge controller to buy. Refer to our topic on MPPT Charge Controllers for more information pertaining to them. So, if you plan to start out with 240 watts of solar panels and possibly upgrade to another 2 panels later on, you'd better size your wiring and charge controller accordingly or else you'll be replacing everything when that time comes. The following shows the ampacity of various wire gauge sizes:
Now that you have the wire gauge chosen, it's time to select what kind of wire you need. You don't need anything fancy to carry the power. Any automotive based low voltage wire is fine. However, you will need to protect this wire from damage. Standard GPT automotive wire is not very resistant to heat or sunlight. GXL wire is a better choice. You also need to protect that wire. You can run the GXL primary wire inside plastic wiring loom then use rubber coated hose clamps to secure fasten it to the RV's roof. Or you can use a pre-shielded cable, such as boat cable, which is commonly used in marine applications. This cable is very similar to the non-metallic shielded cable used in residential construction except it is designed for low voltage use and uses stranded wire, which is more flexible and easier to route than a solid conductor shielded cable. This cable is easier to use because you don't have to wrap a separate layer of wire loom around it.
You also need to get from the roof down to your charge controller, and eventually the batteries. The most popular method is to drill a hole through the refrigerator's roof vent and go down through that area. Be sure to securely fasten the cable away from the hot refrigerator coils to prevent heat damage to the wire. Once you are down past the refrigerator it is generally an easy task to punch through the floor and down into either the kitchen cabinets or basement areas.
Next you will run the cable down to your charge controller. The charge controller is an electronic device so you don't want to locate it next to your batteries or in any area exposed to the elements. It does not generate any sizeable heat though so it need not be placed in a well ventilated compartment. Most charge controllers also feature an optional remote control panel that can be located inside the coach in a convenient location to monitor your solar array status. This panel is connected to the charge controller via a small cat5 data cable.
After leaving the charge controller, the cable now gets connected to your battery bank. You can either run it to the disconnect switch or direct to the batteries. Most RVers run it direct so that the batteries can continue to be charged when the vehicle is in outside storage.
For your reference here is a link to the Installation Manual for the charge controller I used in my installation. Others are similar. Also shown is a link to the Shell-Siemens SM110 solar panel specs. That will give you a general idea as to the physical size and wiring requirements as well as performance ratings of that particular panel. Other panels and charge controllers will be similar. The third item is a quick schematic of how the system on my 2004 Allegro Bus was laid out.
Submitted by Mark Quasius - 2/23/06
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