How long does a solar panel take to charge a battery?
Work out the watt-hours the battery needs, then divide by what the panel really delivers. A 100 Ah, 12 V battery from 50% to full needs 600 Wh. A 200 W panel delivers about 150 Wh per peak sun hour at 75% system efficiency, so it takes 4 peak sun hours. At 5 sun hours a day that is 0.8 days.
Panels rarely hit their rated watts. Heat, the angle to the sun, wiring and the charge controller all take a share, so 70% to 80% of the rating is a fair planning figure. The solar battery charging guide covers controllers and sizing, and the 200 W panel and 100 Ah battery answer works through that common setup.
sun hours = battery Ah x volts x share to fill / (panel watts x efficiency)
Solar charging time chart
Peak sun hours to charge a 12 V battery from 50% to full at 75% system efficiency.
| Battery | 100 W | 200 W | 300 W | 400 W |
|---|---|---|---|---|
| 50 Ah | 4 h | 2 h | 1.3 h | 1 h |
| 100 Ah | 8 h | 4 h | 2.7 h | 2 h |
| 200 Ah | 16 h | 8 h | 5.3 h | 4 h |
| 300 Ah | 24 h | 12 h | 8 h | 6 h |