How much solar to recharge a power station
Updated
The formula
The solar recharge calculator and the runtime calculator use the same three steps, stated on the methodology page:
- Solar input is the smaller of your panel watts and the station's solar input limit.
- Energy a day = solar input × peak sun hours × 0.75.
- Hours of sun to refill = rated capacity ÷ (solar input × 0.75), from empty.
Worked through on the Jackery Explorer 2000 v2, a 2,042 Wh station with a 400 W solar limit:
| Panels | Solar input | Energy a day | Hours of sun to refill | Days to refill |
|---|---|---|---|---|
| 200 W | 200 W | 200 × 4 × 0.75 = 600 Wh | 13.6 h | 3.4 |
| 400 W | 400 W | 400 × 4 × 0.75 = 1,200 Wh | 6.8 h | 1.7 |
| 600 W | 400 W | 400 × 4 × 0.75 = 1,200 Wh | 6.8 h | 1.7 |
The third row shows the cap at work. Panels above 400 W add nothing on this station, so the energy a day stays at 1,200 Wh.
Peak sun hours, not daylight hours
Panels deliver their rated watts only in full sun. Morning and evening light gives a fraction of that. Peak sun hours add up the whole day of uneven light and express it as hours of full sun, so a long summer day counts as fewer peak sun hours than it has hours of daylight.
Our tools start at 4 peak sun hours, a round planning figure, not a claim about your location. Winter, cloud, a low sun angle and shade bring the number down. Enter your own number in either calculator.
Why 0.75
A panel rated 200 W rarely puts 200 W into a battery. Hot panels produce less, a panel that is not facing the sun square on catches less light, and the charge controller and wiring lose some on the way. The 0.75 covers those losses in one factor, so 200 W of panels count as 150 W of charging.
The factor is our assumption, not a measurement. Some days will beat it and some will fall short. We compare your panel watts with the station's limit first and apply the 0.75 after, in the order the methodology states. The refill math also assumes the station charges at the same rate all the way to full.
The station's solar limit
Each station accepts a maximum solar input, and the limits in our data run from 100 W on the BLUETTI Elite 10 Mini to 10,000 W on the EcoFlow DELTA Pro Ultra X. 42 of the 53 stations with a published limit accept 400 W or more, and 24 accept 1,000 W or more. One station has no published solar limit, and the calculators give no solar figure for it rather than an uncapped one.
A watt limit is not the only one. Solar inputs also accept a range of voltage and current, which the maker's manual states. We do not check how your panels are wired, so read that range before you connect panels in series.
Sizing panels to keep up
To run a setup on solar day after day, the panels must put back what the setup uses. Turn the formula around: panel watts = energy a day ÷ (peak sun hours × 0.75). The table works it out for setups from our scenario pages.
| Setup | Energy a day | 3 sun hours | 4 sun hours | 5 sun hours |
|---|---|---|---|---|
| A CPAP for two nights | 88 Wh | 40 W | 30 W | 30 W |
| A refrigerator overnight | 1,300 Wh | 580 W | 440 W | 350 W |
| A home office day | 1,436 Wh | 640 W | 480 W | 390 W |
| Van life | 1,199 Wh | 540 W | 400 W | 320 W |
| Outage essentials | 2,180 Wh | 970 W | 730 W | 590 W |
Van life is the clearest case: 1,199 Wh a day needs about 400 W of panels at 4 sun hours, and 42 of the 53 stations with a published limit accept that much input. Below that, the battery drains a little each day and the gap grows until a wall or car charge closes it.