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Solar Charging Time Calculator

See how long your solar panels take to charge your power station, and check that your wiring stays inside its voltage and current limits.

1Your power station

1,024 Wh · solar input up to 1,000 W · 11–60 V

2Your solar panels

Typical values for this panel class. For accuracy, enter the numbers from your panel's label below.
Wiring (for 2+ panels)
Series adds voltage; parallel adds current. Which should I use?

3Sun & battery

About 3 in winter, 5–6 in summer
Heat, angle and wiring losses
Charging timeDetails

How charging time is calculated

We take the panels' rated watts, apply a real-world factor (75% by default), then cap the result at what your power station's solar input accepts: its maximum watts, and its maximum current at your array's voltage. The energy needed to go from your start to target charge, divided by that input, gives the hours of good sun required.

Hours of sun = Battery Wh × (target% − start%) ÷ min(panel W × 75%, input limit)

Working it out by hand

Say you have a 1,024 Wh power station and one 200 W panel. At 75%, the panel delivers about 150 W in good sun. 1,024 ÷ 150 gives about 6.8 hours of good sun to go from empty to full. With 4.5 peak sun hours a day, that's a day and a half of sunny weather. In winter, with about 3 peak sun hours, it takes more than two days.

The table below runs the same math for common setups. It assumes your power station accepts everything the panels deliver. Small stations often cap solar input (some at 100 to 200 W), so check yours with the calculator above.

Hours of good sun to charge from empty, at 75% of panel rating (sunny days at 4.5 peak sun hours in brackets)
Battery100 W of panels200 W of panels400 W of panels
256 Wh3.4 hours (under a day)1.7 hours (under a day)51 min (under a day)
512 Wh6.8 hours (1.5 days)3.4 hours (under a day)1.7 hours (under a day)
1,024 Wh14 hours (3 days)6.8 hours (1.5 days)3.4 hours (under a day)
2,048 Wh27 hours (6.1 days)14 hours (3 days)6.8 hours (1.5 days)

The wiring check

Every power station has a solar voltage window. Go above the maximum open-circuit voltage (Voc) and you risk damaging it; stay below the minimum and it won't charge. Series wiring adds up voltage, parallel wiring adds up current. The calculator flags both problems, and tells you when extra current is simply wasted. Remember that Voc rises in cold weather, so leave some headroom. More in our solar wiring guide.

Questions

What are peak sun hours?
The number of hours per day your location gets the equivalent of full, direct sun (1,000 watts per square meter). Most of the US gets about 3 to 6 depending on the season and weather, even though the sun is up much longer.
Why do my panels make less than their rated watts?
Panel ratings are measured in lab conditions. Heat, sun angle, haze, dirt and wiring losses usually cut real output to about 70–80% of the rating. This calculator assumes 75%, which you can change.
Is it safe to wire panels in series?
Yes, as long as the combined open-circuit voltage (Voc) stays below your power station's maximum solar input voltage, even on cold days when Voc rises. The calculator warns you when it doesn't.
How long does a 100 W solar panel take to charge a power station?
Plan on about 75 W reaching the battery in good sun. That fills a 500 Wh station in about 6.7 hours of good sun, roughly a day and a half at 4.5 peak sun hours a day, and a 1,000 Wh station in about 13 hours, closer to three days.
How do I work out solar charging time for a 12 V battery rated in amp-hours?
Turn amp-hours into watt-hours first: Wh = Ah × volts. A 12 V 100 Ah lithium (LiFePO4) battery is about 1,280 Wh, since its nominal voltage is 12.8 V. With a 100 W panel delivering about 75 W, that is about 17 hours of good sun, or close to four days at 4.5 peak sun hours. Lead-acid batteries are normally recharged from about half full, so count only half their capacity.
Can I use another brand's panels with my power station?
Usually, if the voltage and current fit the input limits and you have the right adapter cable (for example MC4 to XT60, Anderson or 8 mm). Check your manual for the exact connector.

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