This is the first of a series of articles about adding solar to an RV.
There is no one simple answer to this question.
Since most of us are using lead acid batteries, I’ll start with some information about them.
There are at least two ways to approach batteries for RV’s. One is to consider them the same way as fuel–that is that they are a consumable item that will be “refilled” by replacing them. Another is to try to make the battery bank last for many years.
These two approaches require different sizing.
In the first instance the bank only needs to cover the energy requirements for the “worst case” trip. I.E. to cover the longest time frame. Solar system size would be for maintenance and slow recharging between trips.
The “many years” approach needs a much larger capacity bank where only 50% of the capacity is ever used. The goal for solar would be to recharge the bank to 100% each and every day and to have enough solar wattage to equalize the battery bank. That means a proper energy audit needs to be done.
If hiring an installer, it may be important to know exactly what you want before you darken their door. An otherwise adequate installation may be compromised by poor choice of wire size, poor choice of controller, or shading from other items on the roof of an RV. Use the knowledge you gain from reading this series of posts and insist on them meeting your requirements. If you do, the system may be the nearest thing to a “free lunch” that you are likely to find.
One last comment. Articles become dated as time goes on. So what I have written may evolve from what is best practise today (2016 11 22) to some other method in the future. I’ve tried to avoid this effect somewhat by not posting many links. That means that you, the end user, may have to work a tiny bit harder to get all the ducks in a row.