Solar Panels: How many watts?

hedgehopper wrote:
How many watts of solar panels would I need to keep two 12-volt batteries charged? I don’t know the specs on the batteries. I’m looking for a ballpark number.

What about portable panels vs those mounted on the roof?

The answer to your question highly depends on how many amps you pull out of your batteries each day. For zero amps with battery not being used in storage I would suggest a minimum of 50 Watts for up to 200AH. Use a suitable charge controller with the solar panels.

As Ed said, depends on how much power you draw. So there’s no way to hazard a guess without more information.

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

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

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

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.

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.

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?

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.

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.