How much solar does it take to recharge a 12V 200Ah lithium battery in a day?

Direct answer: Work from energy: refilling from 20% to full is about 2 kWh for a 12V 200Ah LiFePO4 battery. Panel watts needed are that energy divided by peak sun hours and by a loss factor. With 4 peak sun hours and about 25% overall losses, that is roughly 700W of panels; with 6 sun hours, under 500W. Winter can need twice as much. Use your location’s solar data, not a generic number.

Battery energy. The 12V 200Ah page lists 12.8V and about 2,500 Wh; the 12V 200Ah Ultra lists 2,560 Wh. From 20% to 100% is about 2 kWh into the battery.

Sun hours. Peak sun hours are the equivalent hours of full-strength sunlight per day. They vary by location, season, tilt and shading; the NREL PVWatts calculator gives monthly figures for many locations. A flat van roof usually does worse than a tilted fixed array.

Losses. PVWatts uses a default 14% for system losses such as soiling, wiring and mismatch, and models temperature and inverter losses separately. For a small 12V system with a controller and flat-mounted panels, planning on 20 to 30% total losses is a reasonable starting assumption.

Worked example. Energy needed 2,000 Wh, sun hours 4, loss factor 0.75: 2,000 ÷ (4 × 0.75) ≈ 670W, so about 700W of panels. With 6 sun hours: about 450W. With 2 winter sun hours: about 1,330W, which may not fit a van roof; plan alternator or shore charging instead.

Controller. An MPPT controller’s output current is roughly panel watts divided by battery charging voltage: 700W ÷ about 14V ≈ 50A, so choose a controller rated 50A or more at 12V. The battery’s charge rating is not the limit here; the 12V 200Ah lists 100A, 150A or 200A charge versions and the 12V 100Ah 50A or 100A. Set the controller’s lithium profile; see solar controller settings.

Daytime loads. Loads running while the sun is up use solar directly and reduce what reaches the battery. Size for daily use, not just battery size.

Bigger systems. Above about 1 kW of panels, consider whether 24V makes wiring easier; see 12V or 24V for an off-grid cabin.