Solar Panels: How many watts?

I know everyone wants you to do complicated formulas. And even after you do that, the answer will still be different for each individual situation. Nothing wrong with doing the surveys, but you just want some point of reference to get your planning started. The geeks just love to overcomplicate stuff.

So here is my suggestion. Go with a minimum of 1 watt solar panel per 1 AH battery capacity. And figure a maximum of 2 watts solar panel per 1 AH battery capacity. Lean toward the smaller side if budget is important to you. Lean toward the larger side if you like a little overkill, and if you want a good charge on a less than good solar day.

But whatever you do, make sure you have a plan for adding more panels in the future.

400w solar is doing a great job on my 230AH battery bank, which is a pair of 6V. I could add another 200 to 400, because I planned the layout that way, but I've found that I don't need any more. At least not unless I add more batteries.

My scenario is about the same as above except my trailer is not 3 season.
I have 200 watts of solar with 2 GC2 batteries (225 AH total). They are usually at 70% in the morning and fully charged by mid afternoon.

RedRocket204 wrote:
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.

This pretty well describes our situation except that we have a truck camper not a trailer.

Kinda like asking how long is a rope.

red31 wrote:
corrective equalization requires current, 60w/100ah maybe on the low side.

Assumes solar is the only charging method he has. For a weekend warrior it is valid to lose capacity every day with solar just slowing down how much you lose, then charge to full on shore power at home.

How much solar you need is all about scenario.

corrective equalization requires current, 60w/100ah maybe on the low side.

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?

Keeping them charged means they are already charged and you are "maintaining" them. There are solar trickle chargers for that.

If you mean while camping, you don't give any scenario to answer the question.

Generally, you first need an idea how many hours of sunshine you will get in a day, and how many amp hours of battery bank you need to restore daily. Divide the AH by the hours and that's how many amps.

You can find the amps a panel will do at high noon--eg 100w does 6 amps. But the sun goes up and down so you need an average amps over the whole day. Pick a number. That times the hours per day is your expected AH haul.

Get enough solar so you can haul in more than you use daily. Oops except is that in summer or winter? Enough for winter is more than you need for summer and enough for summer is not enough for winter.

pianotuna wrote:
Some where between 60 and 150 watts per 100 amp-hours of storage.

Don

Can you clarify this? I have a 100Ah battery but 50 usable Ah. Would I consider 50 or 100 as my "storage"?

The question of 'how much solar' comes up in my circle from time to time.

I agree with performing a realistic audit

Thanks

My roof would fit 6#, 100 watt panels and still have room to maneuver around. They feed into two 100 amp Battle Born lithium batteries. Will eventually add one more 100 amp battery. The setup easily takes care of my need. My 2000 watt inverter runs our Microwave easily. I haven't come across any restrictions with my current setup.

Some where between 60 and 150 watts per 100 amp-hours of storage.

Do an energy audit so you know how much demand there is.