Solar is the most freedom-giving way to charge an RV battery — park in the sun and the bank fills itself. But "how many panels?" has no single answer; it depends on your daily draw, your sun, and your battery chemistry. Here's a formula you can actually use.
The quick answer
Take your daily amp-hour draw × 12V, divide by your location's peak sun hours, multiply by a ~1.3 loss factor, and you get the panel watts you need. For a typical lightweight RV (≈50Ah/day) that lands around 200–300W of panels. Lithium makes the most of those watts because it accepts partial, irregular solar input without complaint — see our charging guide.
HumsiENK 100Ah LiFePO4 (Bluetooth)
The sizing formula
Panel watts ≈ (Daily Ah × 12V) ÷ Peak-sun-hours × 1.3
- Daily Ah: add up fridge, lights, pump, devices (our bank-sizing guide shows the math).
- Peak sun hours: not daylight hours — the equivalent hours of full-strength sun. ~4–5h in most of the US summer; ~2–3h in winter or under tree cover.
- 1.3 factor: covers controller losses, wiring, temperature, and dirty panels.
MPPT vs PWM
| Controller | Yield | Best for |
|---|---|---|
| MPPT | ~20–30% more from same panels | Lithium, larger arrays, higher panel voltage |
| PWM | Lower, clamps panel to battery voltage | Small, budget 12V setups only |
For any realistic RV lithium build, MPPT wins. It also folds neatly into a DC-DC + MPPT combo charger fed from both solar and alternator — see the charging guide.
Lithium vs AGM on solar
- Lithium soaks up whatever the panels make, even a trickle, and you can use ~100% of capacity — so a smaller panel set covers the same loads.
- AGM wants a proper absorb/bulk/float cycle and only gives ~50% usable capacity, so you need both more panels and a bigger bank for the same runtime.
The voltage chart helps you confirm a lithium bank is actually charging and not just showing surface voltage.
Worked example
Daily draw 50Ah, summer sun 5 peak hours:
50 × 12 = 600Wh ÷ 5h = 120W × 1.3 ≈ 160W. Round up to a 200W panel for margin. Winter (3h sun) doubles that need to ~270W — which is why many full-timers run 300–400W.
Shop the batteries
314Ah LiFePO4 — best for full-timing
Panels, controllers, and combos:
Visit HumsiENK Store Visit Wattcycle Store
Frequently asked questions
How many watts of solar do I need for a 100Ah RV battery?
For light loads (≈40–60Ah/day) a 100Ah lithium bank pairs well with about 200–300W of panels in decent sun. Scale the watts up with your actual daily amp-hour draw.
Do I need MPPT or PWM for RV solar?
MPPT. It harvests roughly 20–30% more from the same panels than PWM and handles the higher panel voltage lithium systems use, so it pays for itself in faster charging.
Will solar alone run my RV off-grid?
For lights, fridge, and devices, often yes with 300W+ and a lithium bank. For an air conditioner you'll need a much larger array plus a big inverter — see our A/C-on-battery guide.
Disclosure: RV Battery Hub is reader-supported and may earn from qualifying links at no extra cost to you. Prices and availability shown on retailer sites are final. This guide is editorial and not sponsored by any manufacturer.