Solar Charge Time Calculator
Estimate how long solar panels take to charge a portable power station, in full sun, partly cloudy, or overcast skies.
Results
Charge time: 7.1 h
Days of charging: 1.4 days
Power reaching the battery: 140 W
Energy to replace: 1,000 Wh
How it works
Panels almost never deliver their rated watts. Derate the rating for the sky you will actually get, then divide the energy the battery still needs by what reaches it.
charge_input_w = panel_w × derate(sky)
energy_needed_wh = capacity_wh × (1 − start_soc / 100)
hours = energy_needed_wh / charge_input_w
days = hours / sun_hours_per_day
capacity_wh- Nameplate battery capacity, from the catalog model or your entry, in watt-hours.
start_soc- How full the battery is before charging starts, in percent.
energy_needed_wh- Energy the charge must replace: capacity × (1 − start_soc / 100).
panel_w- Total rated (STC) wattage of the panels you connect.
derate- Share of the rating that reaches the battery: 0.70 full sun, 0.40 partly cloudy, 0.12 overcast.
charge_input_w- Power actually going into the battery — panel_w × derate.
hours- Hours of that sky condition needed to reach full.
days- Those hours spread across your daily sun window.
Assumptions
- Full sun uses a 0.70 derate covering heat, panel angle, soiling, cable and MPPT losses. It is cross-checked against Jackery's published figure for the Explorer 1000 v2 — 1,070 Wh from 400 W of panels in 3.8 hours implies 0.70. Other published pairings imply about 0.63, so treat full sun as a best case.
- Partly cloudy (0.40) and overcast (0.12) scale the full-sun figure by the middle of the published cloud bands: about 40–70% of clear-sky output under broken cloud, 10–25% under heavy overcast.
- The tool does not know your station's maximum solar input. Panels beyond that limit will not charge any faster, and too much voltage can damage the charge controller — check the spec sheet.
- Charging is treated as constant. Real chargers taper near the top of the pack, so the last 10–20% takes longer than this estimate.
- Sun hours per day is your own charging window, not a cloud-averaged figure. If you substitute NREL peak sun hours, which already average in cloudy days, leave the sky on full sun so cloud losses are not counted twice.
FAQ
How long does it take to charge a power station with solar?
Divide the watt-hours you need by about 70% of your panel rating. A 1,000 Wh station charging from empty on 200 W of panels needs roughly 1,000 ÷ 140 ≈ 7 hours of full sun — more than a single day's charging window at most sites.
Will solar charge a power station on a cloudy day?
Yes, but slowly. Panels still collect diffuse light: expect roughly 40–70% of clear-sky output under broken cloud and 10–25% under heavy overcast. The 200 W of panels that push 140 W into the battery in full sun deliver about 24 W on a dark day.
Can I connect more solar watts than the station's rated input?
Extra watts never charge faster than the station's input cap, and panel voltage above its window can damage the charge controller. Oversizing only helps in weak light — winter sun, haze, poor angles — where the array never reaches the cap anyway.
Sources
Related calculators
Some product links on this site are affiliate links; we may earn a commission at no extra cost to you. Read the Affiliate Disclosure.