How long to recharge with solar

How is solar recharge time calculated?

Hours of strong sun = battery capacity (Wh) ÷ the smaller of your panels' real output (W) and the station's solar input limit (W).

Worked example: 400 W of panels at 75% deliver about 300 W. A 1,024 Wh station with a 500 W solar limit accepts all 300 W, so it needs about 3.4 hours of strong sun, about 0.8 days at 4.5 peak sun hours. Doubling the panels to 800 W would hit the 500 W limit, cutting the time to about 2 hours, not 1.7.

What should you enter in each field of the solar calculator?

Enter your station, your panels' combined rated watts, a realistic peak sun hours figure and the share of the panel rating you expect to get.

Power station

The list shows each model's published capacity and maximum solar input. Capacity sets how much energy you need to put back. The input limit sets the fastest rate the station accepts, however many panels you connect.

Total panel watts

Add up the rated maximum power on each panel's label or spec sheet. Two 200 W panels make 400 W.

Peak sun hours per day

Peak sun hours turn a day of changing light into an equivalent number of hours at full midday strength. The figure depends on location, season and weather, so the calculator can't pick it for you. The default of 4.5 is a middle value. Rerun it at a lower and a higher figure to see your range.

Real-world panel output

This is the share of the panel rating that reaches the station. Our calculator defaults to 75%, our adjustable default rather than a measured figure, so change it to match your panels. Angle, heat, dirt, cables and mismatch each take a share: NREL's PVWatts model sets aside 14% for dirt, shading, wiring, mismatch and similar losses alone (PVWatts Version 5 Manual (NREL/TP-6A20-62641, A. Dobos), National Renewable Energy Laboratory, U.S. DOE, 2014). If your panels lie flat, sit in partial shade or are a few seasons old, step it down a notch or two. Panels also age: NREL's study of US solar fleets found a median drop of 0.75% a year, faster in hot climates (Loss Factor Assessment in the 8GW PV Fleet Performance Data Initiative (DuraMAT virtual seminar slides, Deline & Muller), National Renewable Energy Laboratory, U.S. DOE, 2022).

How do you read the result and the red "station accepts X W max" chip?

The big number is the hours of strong sun from empty to full, converted below into days at your peak sun hours. The chip tells you whether your panels or your station is the bottleneck.

A plain chip reads "Charging at ~300 W of 500 W max". Your panels are the limit, so more panel watts cut the time. A red chip reads something like "Panels give ~600 W; station accepts 500 W max". Now the station is the limit, and extra panel watts do nothing.

A result of 0.8 days means one sunny day should do. A result of 2.3 days means three days of decent sun, or a top-up from a wall outlet.

How many days does 400 W of solar take to recharge a power station?

From a fraction of a day for a small station to several days for a large one. The table uses 400 W of panels at 75% output. The last column shows the panel watts needed to reach each station's input limit.

The Yeti 300 is already capped at 400 W of panels. The Yeti PRO 4000 needs ten times the panels before it hits its limit. For more models, see the best power stations for solar charging.

Should you buy more panels or a station with a higher solar input?

Buy more panels while the chip is plain. Once it turns red, only a station with a higher solar input will charge faster.

Worked example: the Jackery Explorer 2000 v2 stores 2,042 Wh and accepts up to 400 W of solar. With 400 W of panels at 75%, it charges at about 300 W and needs about 6.8 hours of strong sun. Adding panels up to 533 W (400 ÷ 0.75) brings it to the 400 W limit and cuts the time to about 5.1 hours. Past that, extra panels change nothing.

Compare the Goal Zero Yeti PRO 4000, at 3,994 Wh and 3,000 W of solar input. With 400 W of panels it needs about 13.3 hours. Doubling to 800 W cuts that to about 6.7 hours, and it keeps improving all the way to about 4,000 W of panels.

For a full recharge in one day, divide the capacity by your peak sun hours. Pick a station whose solar input clears that, then buy enough panels to supply it. Across the 51 models that publish a figure, solar input runs from 100 W to 4,000 W, with a median of 800 W. Browse stations of 3,000 Wh and up for the highest limits.

What happens if you run devices while charging from solar?

Loads take their share first, and only what's left reaches the battery. The calculator assumes no loads, so charging will take longer.

Say your panels deliver 300 W and your devices pull 100 W. About 100 W less is left for charging, so the station from the example above would need about 10.2 hours of strong sun instead of 6.8. AC loads cost more than their label wattage: at the site's 85% efficiency assumption, an 85 W AC load pulls about 100 W. The inverter also draws power just by being on: Sandia's model puts that at about 1% of the inverter's rated power (Performance Model for Grid-Connected Photovoltaic Inverters (SAND2007-5036, King et al.), Sandia National Laboratories, U.S. DOE, 2007). Turn the AC outlets off when you only need USB or 12 V. To see how long loads run after sunset, use the power station runtime calculator.

Why isn't my power station in the solar calculator?

The calculator lists only models whose maker publishes a maximum solar input. Of the 56 models we track, 5 don't publish one, so we can't calculate their recharge time without guessing.

Check your manual for a solar or DC input rating (watts = volts × amps), then use a listed station with similar capacity and input as a stand-in. The comparison pages help.

What can't the solar calculator account for?

It can't see your sky, panels or wiring. Treat the result as a planning estimate.

• Weather and shade. Clouds or a shadow on one panel can cut output far below your percentage.
• Panel voltage. A station accepts solar only within a voltage range. The guide to solar charging a power station covers wiring panels in series or parallel.
• The last part of the charge. The calculator assumes a steady rate. Batteries can charge more slowly near full.