Solar Panels: How many watts?

I use a renology kit with 2 100 watt panels and 30a controller i bought off amazon and it works great to charge 2 12volt rv batteries and 2 12volt boat batteries at home. I mounted the panels on an old 2 wheel hand dolly to make them easily to move and manuever. We dont boondock but if we did i would build portable frames with adjustable tilts out of pvc tubing from plans i found on google.

Unless you're actively going to move the portable panels and tilt/position them multiple times a day to see that they produce significantly more than mounted panels, I think Mounted are the way to go. Mounted seem to have better/longer warranties and they are pretty much mount and forget about them. Portables you have to have a decent place to store and then there's the setup, hook up and tear down every time you go camping. Just my two cents.

If your just looking to maintain the batteries between uses, 1-100 watt panel will do that easily. If your looking to keep the batteries charged while camping, an assessment of what you use would be critical to getting that decision right.

Identify what batteries you have so you can figure out how many Amp Hours (AH) they have. Generally, you only want to use 50% of those AH because going below that damages the battery and makes it store less energy upon future recharges.
I'm just going to make up some numbers to illustrate.

So say your batteries are 50AH each. You can take them down to 25AH each without damaging them but then they need a recharge.

So that gives you 25 AH of power to use between fully charged and need to stop and recharge. Now if your your usage is only 10AH a day, you will have 2.5 days of power without solar. If your usage is 25AH a day, you need to recharge daily and more importantly, you need to fully charge your batteries to be able to use your full 25AH again the next day. If they don't get fully charged, your going to be using more than 50% and damaging your batteries if you use your typical 25AH.

Next thing to consider is that solar panels are rated for a specific output but that is is optimal conditions. If you partially shaded because of a tree, or it's a partly cloudy day, or worse yet, it rains all day and you get nothing from the panels. So you want a generator as a backup plan for those days or if you need to assist the panels in getting back to 100% charged batteries. But many people put as many panels as they can which gives a quicker recovery of their batteries but most importantly, gives them a chance to get fully recharged to 100% even if they only get a partial day of sun.

The last consideration is going back to the Batteries. Adding more powerful 12v or (2 or 4-6v in parallel is the favorite configuration for many people) batteries that have higher AH ratings (Stores more power) makes your energy piggy bank much bigger. If you had 2 batteries that gave you a total of 300AH and you could use 150AH a day (Remember the 50% rule), well now your 25AH usage isn't such a big deal. You have 6 days worth of usable energy. A couple cloudy days wouldn't even make you fire up the genny.

Even though the numbers are made up just to make the math easy, I hope this helps you understand the process of deciding what is right for you (and others that may read this). There are a lot of moving pieces to think about but it really boils down to these three things:

* How much energy do you use/need daily
* How much can your batteries store
* How much can the panels reasonably put back in a day

Until you know the first one, it's like asking how much water should I take on my desert hike?

(Usage) How much do you need to drink each day?
(Batteries) How much can you carry?
(Solar Panels) Are there any oasis's to refill along the way?

I have 250 watts. It's what fit on my roof. That will be your most limiting factor anyway. This amount will keep my batteries charged indefinitely if I'm camping in the sun. Even in winter when I'm running the heater fan.
It's a best practice to reduce amperage use in the RV as much as possible to preserve battery storage. LED lights for example.

I have 150 watts.

To maintain the batteries between trips, and long term, it's WAY more than enough.

To just do some basic camping, using mostly propane, but watching a movie or two at night, charging phones/tablets, water pump, lights, some furnace, I can go at least 4 nights before worrying about recharging my 2 batteries. Likely longer, and that's typically in partial shade.

Your mileage may vary. Like posted earlier, if you're considering going to the trouble of permanent mounting, go for as much as you can swing.

Portable panels are the best! Set them up in the morning but your neighbor’s roof mounted panels are already charging. Watch them for theft! Going out to lunch or for a bike ride? Take them in to prevent theft. Come back, set them back up...watch for theft. Starting to get dark...put panels away. And where do you put them?

My daily use is around 100 ah. I have a "400" watt kit that so far has made a max of 300 watts during the hours when the sun is high in the sky. At that speed I need abour 8 hours of sun to fill my batteries from 50% state of charge to full. I have led lighting and I run my fridge on propane. I have a 430 ah battery bank and I live where it's sunny all the time. Two twelve volt batteries have less capacity than I have and your use might very well be more than mine. You can supplement with a generator as well and it depends on sun. I recommend getting the largest setup you can afford. The modest difference in price will pay off with longer battery life if you can keep your batteries at a higher state of charge and reduce discharge cycles.

My recommendation is to definitely buy the largest solar charge controller you can to give room for growth if you need more panels. I can add a fifth panel to mine, but if I buy more panels I may add three more and use series/parallel to ensure I don't exceed the 100 volt/40 amp rating. In theory I'm limited to 530 watts but solar panels won't ever make their full output without tilting and maybe not even then, so I've contemplated installing 600 watts of solar in that configuration to max my controller out as I doubt I'd exceed any of my other ratings under normal conditions.

200W will get me by with limited usage of 12V items in the CO mountains, late fall boondocking. That includes 2-3 hours of some LED lighting, USB phone charging, CO detector, fridge running on propane, some water pump usage and the big one, heater fan kicking on with the thermostat set at 52f and outside temps dropping into the teens f. My TT is considered a 3-season trailer with decent insulation but I don't have separate tank heaters. With two Group 24 12V batteries, I do get pretty close to 50% discharge rate by the time the sun comes up.

I've since added a 1500W inverter and will be changing up to (2) GC2 6V batteries along with possibly adding an additional 200W solar panels if I need them. If I do add solar panels, I will add to the mounted panels as I don't want to bother with portable units. With mounted panels, I just need to be sure and set-up with no trees above.

All solar projects start with an energy survey...actual use or desired use.

For the effort I would go 100 watts minimum. Then add usage.

Not only do we not know how much you are using but you have to return more than you used