We think that there is no better feeling than to be self sufficient for the electricity in your RV. No more having to worry about finding a place to plug in, no worries about whether it's stable source of electricity, and no need to buy surge protectors or voltage regulators.
Solar panels designed for RV use are rated in watts. You can buy single solar panels rated as low as 5 watts, or as high as 250 watts. Of course the 5 watt panel is very small, and the 250 watt panel is very large.
It is most common to find single RV solar panels rated between 80 watts and 150 watts. Simply due to size restrictions on roof space, these solar panels are the easiest to mount and make the most use of the roof space available.
The number of total watts that you will want will depend on two things.
1) How much battery capacity you have.
2) How much sunshine you have,
It is fairly standard, both from what I have read, and our own personal experience, that you want around 80 watts of solar power for every single deep cycle battery that you have. So, if you have two 6 volt deep cycle batteries, you will want approximately 160 watts worth of solar panels on your roof.
These numbers are not written in stone though. If you have lots of sunshine available, and you don't draw down your batteries very much in the evening then you can get by with less solar panel power. If you are a heavy user and/or have a lot of cloudy days then you may need more than 80 watts of solar per battery.
We have four deep cycle batteries but only three 80 watt panels. But we find this sufficient for our needs. On a sunny day, our batteries are usually fully charged again by noon the next day.
RV solar panels do not supply exactly 12 volts. In fact, most of them are rated to supply between 17 and 22 volts. So besides the solar panels, you also need a solar charge controller to electronically control the voltage and current being supplied to the batteries from the solar panels.
You can spend a lot of money on charge controllers! But, you don't need to.
We have a basic charge controller that is now 7 years old. It has done, and continues to do a good job. But not a great job. I have often thought of buying a better quality charge controller, but I can't justify the money for perhaps a 10% to 20% gain in efficiency.
Our charge controller.
The neat thing about RV solar panels is that you can start small and add panels as you need to. When we first bought our kit, it included two 80 watt panels and a 30 amp maximum charge controller. In full sunlight, each 80 watt panel will output about 5 amps. So we could have a total of six of these panels matched with that particular charge controller.
After using the system for a year, we decided that one more 80 watt panel would be better for our needs and usage, so we simply added another panel to the roof and ran another set of wires to the charge controller.
RV solar panel kits have come way down in price since we bought ours. You can now buy a 100 watt starter kit including the mounting brackets, wiring, and charge controller for under $200 USD. For that kind of money, I don't understand why anybody wouldn't have one installed. Of course you still need to pay for installation, but if you are at all mechanically minded you could easily do it yourself.
For a beginner, this is the kit I would recommend...
As I said, the solar system can be added to over time. Simply buy another panel, or two, and wire them to the existing charge controller. If money is no object, you can even upgrade charge controllers to get one with a display or fancier electronics that charge your batteries more efficiently.