Hi,
Yes you can. However 45 watts is not nearly as much power as your RV is using each day. My motorhome has a E-meter installed in it. While the CO and propane detectors are on, it is drawing 0.8 amps per hour, and when the refrigerator is on, then a total of 1.2 amps per hour, or roughly 35 amp hours per day, or about what one of my pair of 120 watt solar panels can put out daily.
Check out this website, and look for a 12 volt "Nominal" solar panel. It will have a 20 volt open circuit voltage, and that is enough to charge a 12 volt battery at about 14 volts (while charging).
SunElec.comI am not saying that Harbor Freight price is bad, but SunElec.com sells 100 watt panels for about $80 to $120, depending on the brand. You will also need a solar controller, a PWM can use 12 volt nominal panels and works great at a much lower price than a MPPT controller.
You should also consider mounting it on the roof all the time. I used 6" long 2" angle aluminum from Home Depot, and then drill a 5/16" hole for a 1/4-20 bolt into the panel and 3 holes 3/16" for #10 screws into the rubber roof. Using sticky rubber roof adhesive, it will seal the aluminum to the roof and it will both not leak and that large surface area will keep it stuck to the roof.
I ran the #10 wires down the back of my refrigerator with the help of a metal coat hanger. Then to the controller, then to the battery. You can use the battery while charging, just like when plugged into shore power. You can also plug into shore power or not, depending on your needs. It will not matter to have both charging at the same time. Just if you are at a campground plugged in, your solar will probably shut off if the battery is full, and don't worry about that.
Fred.
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