I have an RV which has two new (1 year) AGM deep cycle batteries, total 100 amp hours. They charge from either 30 AMP shore power, generator or vehicle alternator. (1) The RV is "wired for solar" which I believe means only that connections to roof mounted MC4 connectors are available on the power display panel. (2)Ideally I'd like to install 2 roof mount solar panels total 370 watts, and then have a (3) portable solar panel which plugs into an MC4 connector on the side of the RV so that the panel can be moved into full sunlight when the RV is parked in the shade.
I'm unsure as to how the system should be correctly wired so that it doesn't run afoul of the transfer switch. (4)If I wire the output from the controller to the battery through a fused wire is that okay? (5) What happens when the alternator is charging while driving, or if I'm plugged into (6) shore power. (7)Does the solar controller throttle back charging if it senses the other power inputs?
I'll probably have more questions later. Thanks for your patience.
The concept is a great idea. Keep cool in the shade and harvest energy in the sun.
Having a 12V system means you're very much current limited. It's going to be hard to have much more than 1200W of solar even with a monster controller. 740W is going to take a 740/12=62A charge controller alone. Adding more on the ground adds some details.
(1) Sounds right. They basically just wire it for you.
(2) Good idea, but 370W panels are absolute monsters. I would seriously consider smaller panels, see (3). RV roofs have lots of little things that shade panels. Shading a big panel hurts output notably. Shading one out of several panels has less impact on total power.
(3) Anything you have on the roof kinda needs to be matched on the ground if you ever want to run them at the same time, or you need provisions for selecting which group you want to use - a circuit breaker for the roof panels and a circuit breaker for the ground panels.
(4) Yes. Or a breaker.
(5) Nothing bad.
(6) Nothing bad.
(7) No. It's oblivious to anything else charging the system. It's looking at the battery voltage and responding accordingly. If other charging systems are raising the battery voltage, then it responds according to its internal rules.
Let's say your panels on the roof are 48V and you wire them in series. You have 96V coming into the controller - not an issue for most MPPT controllers. If you wire your ground panels in parallel to the roof panels, you need to have the same configuration. In short, it's easiest to have ONE type of panel connected to a single charge controller. I would be shocked if you have a space in your RV where you could stow your deployable ground panels. I had to wedge my 330W panels into the bedroom and bathroom in our 33' Class A when I transported them.
12 100W panels would likely give you MUCH more flexibility. You could exploit more favorable mounting areas and orientations and then have 4X 100W deployable panels, which are light and easy to configure. On the roof, the 8 panels would be 4 in series, 2 in parallel and then your ground panels would just be 4 in series. 100W may not be the magic number, but you should likely size ALL your panels based on the size you're willing to carry around.
