How much solar to charge a 200Ah battery

“How many panels do I need for a 200 Ah battery?” is one of the most common RV solar questions, and the honest answer is that the battery is only half of it. Solar should be sized to what you use each day in your weakest travel month. Here is how to think about both, with numbers from the RVWatt calculator and NASA sun data.

What a 200 Ah battery holds

A 12 V 200 Ah LiFePO4 bank stores about 2,400 Wh on paper. RVWatt plans on using 80%, so refilling it from 20% to full means putting back about 1,920 Wh. A 200 Ah AGM bank used to 50% needs about 1,200 Wh put back, but AGM loses more energy while charging and needs a long, slow finish to get truly full.

Solar to refill it in one day

The calculator’s rule is: stored watt-hours per day = panel watts × peak sun hours × 0.757 (the default system factor with an MPPT controller and LiFePO4; it is 0.677 for AGM). So the panel watts to put back 1,920 Wh in one day are 1,920 ÷ (peak sun hours × 0.757). The table also shows what a common 400 W array stores in a day, and how many days it takes 400 W to refill a 200 Ah lithium bank from 20% to full with nothing else running.

Place and month (flat roof)	Peak sun hours	Solar to refill 1,920 Wh in a day	What 400 W stores per day	Days for 400 W to refill
Hailey, ID, July	7.69	330 W	2,328 Wh	0.8
Denver, CO, July	7.00	362 W	2,119 Wh	0.9
Moab, UT, October	4.34	584 W	1,314 Wh	1.5
Denver, CO, October	3.98	637 W	1,205 Wh	1.6
Phoenix, AZ, December	3.08	824 W	933 Wh	2.1
Seattle, WA, October	2.28	1,113 W	690 Wh	2.8
Hailey, ID, December	1.54	1,647 W	466 Wh	4.1

A handy rule of thumb from the same math: one 200 W panel on a flat roof stores about 200 × peak sun hours × 0.757 watt-hours a day. In Denver in October that is about 603 Wh, or roughly 50 Ah at 12 V. Month and place matter far more than the battery size; see peak sun hours by place.

The better question: does it cover your day?

You rarely run a bank flat and then wait for it to refill. You use some energy every day and the panels put some back. So the useful test is whether the panels replace a day of use in your weakest month, and whether the battery carries you through a night and a cloudy day or two. The calculator’s “check my setup” mode does exactly that. Here is a 400 W solar, 200 Ah lithium setup against three presets:

Rig, place and season	Daily use	Days of battery with no sun	Share of a day’s use the solar covers, weakest month	Result
Weekender van, Denver, May–October	830 Wh	2.3	145%	Covers every month
Weekender van, Seattle, May–October	830 Wh	2.3	83%	Short in October; about 81 W more solar
Full-time van, Denver, May–October	2,103 Wh	0.9	57%	Short in May, August, September and October; about 298 W more solar

So 400 W with 200 Ah is a good fit for a weekend van in a sunny summer, light for a cloudy coast in fall, and too small for a full-time setup with a laptop, internet and induction cooking. If your own result comes up short, the calculator shows how much solar or battery to add, or you can add alternator charging and see the gap shrink. Full worked examples are in the camper van and travel trailer guides.

Check 400 W and 200 Ah on the weekender van Same setup on the full-time van

Controller and charge rate

The calculator sizes an MPPT controller as array watts ÷ battery voltage × 1.25. At 12 V, 400 W needs a 50 A controller and 600 W needs a 70 A controller. A 50 A charge into a 200 Ah bank is 0.25C, which is within what most LiFePO4 batteries accept, but check your battery’s maximum charge current, especially for AGM and in cold weather. Most LiFePO4 batteries must not be charged below 0 °C (32 °F).

With a PWM controller instead of MPPT, the same panels store noticeably less; see MPPT vs PWM. Put a fuse rated for the battery’s short-circuit current near the battery, fuse the controller output, and follow the panel and controller manuals for the PV side. If you are not confident with the wiring, have a qualified RV or marine electrician check it.

Frequently asked questions

How many solar panels do I need to charge a 200Ah battery?

To put back the 1,920 Wh RVWatt plans on using from a 12 V 200 Ah LiFePO4 bank in a single day, you need about 362 W of panels in a Denver July but about 637 W in a Denver October, and over 1,600 W in a Hailey, Idaho December. Most people do not need to refill from empty daily, so size solar to your daily use in your weakest travel month instead.

Is 400 watts of solar enough for a 200Ah battery?

For a weekend van using 830 Wh a day in Denver from May to October, yes: 400 W covers about 145% of a day’s use in October, and 200 Ah gives about 2.3 days with no sun. For a full-time van using about 2,103 Wh a day, 400 W covers only about 57% in October. It depends on your loads and season, not on the battery.

How long does it take 200 watts of solar to charge a 200Ah battery?

With the calculator’s defaults, one 200 W panel stores about 200 × peak sun hours × 0.757 Wh a day. In Denver in October that is about 603 Wh, so refilling 1,920 Wh takes about three days with nothing else running. In a Denver July it is about 1,060 Wh a day, so a little under two days.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.