Solar input explained
A power station's solar input rating is the most watts it will accept from panels. It is also the spec most often misread.
The three numbers that matter
- Maximum input watts: the ceiling. A 400 W rating means no more than 400 W reaches the battery no matter how many panels you connect.
- Voltage window: the range of panel voltage the charge controller accepts, written like 11–60 V. Panels wired in series add their voltages; exceed the top of the window and the unit will refuse to charge or, on some models, be damaged.
- Maximum current: usually 10 to 15 A. Panels wired in parallel add their currents.
Every modern unit uses an MPPT controller, which continuously finds the voltage at which the panels produce the most power. Older or cheaper units use PWM, which wastes a meaningful fraction of the panel's output.
Real recharge time
Panels produce their rated wattage only in full, direct sun at a right angle. In practice expect 60 to 75 percent of the rating at midday and far less early, late or under haze. A rough rule: over a good day, a panel yields about four to five times its rated wattage in watt-hours.
- 200 W of panel → roughly 800 to 1,000 Wh a day
- 400 W → roughly 1,600 to 2,000 Wh a day
So a 1 kWh unit refills in about a day on 200 W of panel, and in a long morning on 400 W. A 4 kWh unit with a 1,600 W input can refill in a day, but only with 1,600 W of panel, which is a serious installation.
Sizing panels to the input
Match or slightly exceed the input rating; a 450 W array on a 400 W input loses only the sliver above 400 W but captures more in weak light. Check the voltage window before wiring in series. Folding portable panels are convenient and expensive per watt; rigid residential panels cost a third as much per watt and work fine with the right cable.
What we score
The feature rating gives credit to units accepting 400 W or more, because that is the threshold where a day of sun refills a medium-class unit. See the best units for solar charging.