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How many watts of solar does it take to recharge a 1 kWh power station in one day?
Short answer: on an average day in Phoenix, about 210 to 235 W of solar panels, aimed at the sun, can refill a 1,000 to 1,150 Wh power station from empty in one day under the planning assumptions below. A December day in Phoenix needs about 250 to 285 W. In cloudier places the number goes up fast. Chicago needs about 300 to 350 W on an average day and over 500 W in December. A December day in Seattle can need roughly 850 to 950 W, which is more than most 1 kWh stations can take in at once. Here is where those numbers come from, so you can redo the math for your own panels and location.
The formula
Panel watts needed ≈ battery capacity (Wh) ÷ (peak sun hours × derate)
- Battery capacity is the rated Wh from the spec sheet. Our comparison table lists it for every model.
- Peak sun hours is the day's total sunlight on the panel, expressed as the number of hours of full-strength sun (1,000 watts per square meter) it adds up to. A day with 6.5 peak sun hours delivers about as much energy as 6.5 hours of full noon sun, even though the sun is up longer than that.
- Derate covers everything that keeps a panel from delivering its label rating to the battery: heat, dust, imperfect angle, wiring, and the station's own charging losses. This page assumes 75%. That is our planning assumption, not a measured figure for any panel or station. A hot, dusty panel lying flat may do worse; a clean panel you re-aim every couple of hours may do better.
The same formula works backward. Wh you can expect from your panels in one day ≈ panel watts × peak sun hours × 0.75.
Peak sun hours by city (NREL PVWatts data)
These figures come from PVWatts, the free solar calculator from NREL (the lab was renamed the National Laboratory of the Rockies, NLR, in December 2025). We ran PVWatts version 8 on 2026-11-02 for a south-facing panel tilted at each city's latitude, using the NSRDB typical-year weather data (PVWatts, PVWatts API documentation, DOE notice of the NREL rename). The values are the average daily solar energy on the panel, in kWh per square meter per day, which equals peak sun hours.
- Phoenix, AZ: 6.57 on average across the year. Lowest month December (5.45), highest April (7.48). July, in monsoon season, averages 6.62.
- Tucson, AZ: 6.58 on average. December 5.45, May 7.47.
- Flagstaff, AZ: 6.27 on average. December 5.17. July drops to 5.56 when monsoon clouds build.
- Denver, CO: 5.74 on average. December 4.56.
- Miami, FL: 5.57 on average. December 4.70.
- Chicago, IL: 4.46 on average. December 2.66.
- Seattle, WA: 3.83 on average. December 1.59, November 1.89.
These are averages for a typical year. Any single day can be much worse. A monsoon storm, wildfire smoke, or a gray winter week can cut one day's harvest to a fraction of the average. Use the lowest month for the season you care about if you need the station full every evening.
Panel watts for a full recharge in one day
Using the formula, the 75% derate, and the PVWatts numbers above, here is roughly how much panel wattage it takes to go from empty to full in one day:
- About 1,024 Wh (EcoFlow DELTA 3, EcoFlow DELTA 3 Classic, BLUETTI Elite 100 V2, Anker SOLIX C1000 Gen 2): Phoenix about 210 W on an average day and 250 W in December. Denver about 240 W and 300 W. Miami about 245 W and 290 W. Chicago about 305 W and 515 W. Seattle about 355 W and 860 W.
- About 1,056 to 1,070 Wh (Anker SOLIX C1000X, Jackery Explorer 1000 v2): Phoenix about 215 W and 260 W. Chicago about 320 W and 535 W. Seattle about 370 W and 890 W.
- About 1,152 Wh (BLUETTI AC180): Phoenix about 235 W and 280 W. Chicago about 345 W and 575 W. Seattle about 400 W and 965 W.
- About 768 Wh (EcoFlow RIVER 2 Pro, for comparison): Phoenix about 155 W and 190 W. Chicago about 230 W and 385 W.
In practice, panels are sold in round sizes, so in Phoenix a 200 W panel gets you most of the way on an average day and a 300 W setup covers a typical winter day for a 1 kWh-class station. If you only need to refill half the battery each day (for example, after running a fridge overnight), halve these numbers.
Check the station's maximum solar input
Every station caps how much solar power it will accept. Panels larger than that limit cannot push energy in any faster at midday. Maximum solar input for the 1 kWh-class models in our table, as listed on each brand's official product page (checked 2026-11-02; source pages are recorded in our station data, and the comparison table links to each model):
- EcoFlow RIVER 2 Pro: 220 W, 11 to 50 V
- EcoFlow DELTA 3: 500 W, 11 to 60 V
- EcoFlow DELTA 3 Classic: 500 W
- Jackery Explorer 1000 v2: 400 W total across two DC8020 inputs
- BLUETTI Elite 100 V2: 1,000 W, 12 to 60 V
- BLUETTI AC180: 500 W, 12 to 60 V
- Anker SOLIX C1000 Gen 2: 600 W, 60 V max
- Anker SOLIX C1000X: 600 W, 11 to 60 V
All of these accept enough solar to refill in one average Phoenix day, including winter. The RIVER 2 Pro's 220 W limit is enough for its smaller 768 Wh battery in Phoenix but not for a Chicago December day.
The limits start to matter in cloudy places. On a Seattle December day, a station capped at 400 or 500 W cannot refill a 1 kWh battery with panels sized to its limit. Under our assumptions, 400 W of panels yields about 480 Wh and 500 W about 600 Wh that day. Some brands allow connecting more panel wattage than the input limit so the station stays near its cap for more of a dim day, but voltage and current limits still apply. Check the manual before you go past the rated input, and never exceed the station's maximum input voltage. In those conditions, plan on two days of sun or a wall or car top-up.
Things that change the result
- Aim. The PVWatts figures assume a panel tilted toward the south at a fixed angle. A folding panel propped up and turned toward the sun a few times a day can beat that. One lying flat on the ground in winter will fall short.
- Heat. Solar panels lose output as they get hot, which is part of why we use a 75% derate for Arizona summers instead of something closer to a panel's label. Keep the station itself in the shade, too. Many stations slow or pause charging when they get too hot, so check your manual for its charging temperature range.
- Shade. Even partial shade on one corner of a panel can cut output sharply. Set up away from trees, poles, and vehicles, and remember shadows move.
- What you run while charging. Anything plugged in during the day uses up part of the solar harvest before it reaches the battery. Use the runtime calculator to estimate your daily load, then add it to the capacity you need to refill.
- Brand charge-time claims. Spec-sheet charge times such as "full in 3 hours with 500 W of solar" assume the panels deliver their full rating the whole time. Real-world times run longer, so the formula above is a better planning tool.
Picking a station for solar
If solar recharging is the main plan, sort the comparison table by $/Wh and then compare the maximum solar input limits listed above. In Phoenix, almost any 1 kWh-class station works with about 200 to 300 W of panels. In cloudier regions, or if you want to fill a larger battery in one day, a higher solar input limit (600 W and up) gives more room. Prices on the table are from official brand pages and were last checked on the date shown in each row. They change often, so confirm the current price before you buy.
For what a fridge needs per day, see what size power station runs a refrigerator. For broader outage planning, see home backup essentials.
