Solar charging time: panel watts, sun hours and real-world derating

Solar charging time is the empty part of the battery divided by what the panels really deliver: the panel watts the station accepts, times about 75% for real-world losses. That gives hours of full sun, which you spread over the peak sun hours your location gets in a day. A 400 W panel refills an empty Jackery Explorer 1000 v2 in about 3.6 h of full sun, or 0.8 days at a typical 4.5 sun hours.

The three numbers that set the time

• Panel watts, capped by the station. Every station publishes a maximum solar input. Panels above it are clipped, so extra panels add nothing once you hit the cap.
• Derating. A panel's rating comes from standard test conditions. Outdoors it loses to heat, dust, wiring, imperfect angle and the charge controller. NREL's PVWatts model already assumes 14% of system losses before heat is counted (NREL PVWatts system losses), so the calculator plans on 75% of the rating.
• Peak sun hours. One peak sun hour is 1 kWh of sunlight on a square meter. An NREL presentation gives about 4.5 for Colorado and 3 to 6 across most of the continental US (NREL solar basics, U.S. DOE). The calculator uses 3 for winter or cloudy places, 4.5 as a typical average and 6 for summer in the Southwest.

Sun hours are not daylight hours. A summer day can have 14 hours of light and still deliver only 6 peak sun hours, because morning and evening light is weak.

Worked example 1: one 200 W panel on a 1 kWh station at 20%

Inputs: the Jackery Explorer 1000 v2 (1,070 Wh, 400 W max solar input), starting at 20%, with a single 200 W panel.

Charge times are rounded up and runtimes rounded down, so we never understate the wait or overstate the runtime. One panel is a top-up, not a same-day refill, outside the sunniest months. It suits a camping trip where the station runs lights and phones at night and the panel replaces that the next day.

Worked example 2: the same 800 W array on two stations

Inputs: 800 W of panels, both stations starting empty, 4.5 peak sun hours. The Explorer 1000 v2 accepts 400 W; the DELTA 3 Plus accepts 1,000 W.

Half of the array is wasted on the Explorer 1000 v2. On the DELTA 3 Plus all 800 W count, so it refills a similar battery in about half the sun. If you already own panels, match them to the input limit; if you are buying both, the limit is worth checking before the capacity. The two are compared in DELTA 3 Plus vs Explorer 1000 v2.

Recharge days for 1 kWh class stations

Days from empty to full at 4.5 peak sun hours and 75% derating. Maximum solar input is the figure each maker publishes; capacity and limits come from the product dataset.

"Capped" means the panels exceed the station's limit and the time stops improving. The BLUETTI AC180 and Anker SOLIX C1000 sit in the middle; see C1000 vs AC180.

What changes the answer

• Season and latitude. Going from 6 to 3 sun hours doubles the days. Plan for the season you will actually rely on solar, usually winter for outages.
• Panel voltage and connector limits. The watt cap is not the only limit. Many stations also cap input voltage or current, and a panel string outside that window charges slowly or not at all. Check the manual's input range before wiring panels in series.
• Using power while charging. Anything plugged in comes out of the solar harvest first, so the battery fills more slowly than the table shows.
• Shade and angle. Shade on a few cells can cut a panel's output by far more than the shaded area suggests. A portable panel laid flat in winter loses far more than the 25% allowance.
• Heat. Panels lose output as they get hotter, which is why a clear, cool spring day can beat a hot summer afternoon.