A 12V solar panel with a 20 amp rating generates approximately 240 watts. This is calculated using the formula Power (Watts) = Voltage (Volts) x Current (Amps). But wait – inverters aren't 100% efficient. Most lose 10-15% energy during conversion. Real-World Example: A 240W load actually requires: 240W ÷ 0. 85 (85% efficiency) ≈ 282W inverter capacity Sarah's solar-powered cabin used a 500W. To charge a 12V battery with a 100 amp hour capacity in about five hours, you need a solar panel that produces at least 240 watts (20 amps x 12 volts). Next, assess the solar panel. One 12V 20Ah LiFePO4 Battery, two 100W Monocrystalline Solar Panels, one 20A PWM Solar Charge Controller, one pair 10ft 12AWG Solar Cables, one pair 6ft 12AWG Battery Cables, two set Solar Panel Mounting Brackets, and one set Y Branch Adapter Cable One 12V 20Ah LiFePO4 Battery, two 100W.