Solar Panel and Power Station Recharge Calculator
Daily watt-hours (optimistic upper bound) ≈ min(panel watts, station solar-input cap) × peak sun hours. A 400 W panel into a station capped at 400 W in NREL’s 4.9 sun-hour Colorado horizontal example gives 400 × 4.9 = 1,960 Wh, an optimistic ceiling, not a forecast for your city or a portable panel.
We have not measured panels in the field. These are calculations from published limits and your inputs, not tested recharge times. Get your own plane-of-array sun-hour figure from PVWatts; the calculator leaves sun hours blank until you enter them or choose the illustration.
Estimate a day’s solar input
Enter panel nameplate watts, the station’s solar-input maximum, and your own peak sun hours. No location or weather is assumed.
Your optimistic daily ceiling
Check inputs: panel and cap must be finite numbers greater than zero. Peak sun hours must be zero or more. The calculated daily Wh must be finite.
- Daily input (optimistic upper bound)
- Enter peak sun hours
- Limited watts used
- Enable JavaScript
- Ideal sun-hours to target, no conversion loss
No sun-hours assumed. The 4.9 illustration is used only if you select it.
Target Wh must be a finite number greater than zero and produce finite ideal sun-hours.
This ignores soiling, shade, poor tilt, temperature, cable loss, and imperfect aiming. Real days are often lower. Weather and shade can reduce the day’s input to zero. This is not measured energy stored in your battery or a guarantee of a full recharge.
Inputs stay in this page’s URL, not an account. Copying a link shares panel watts, cap, sun hours, optional target, and selected examples.
400 W at 4.9 sun-hours is a ceiling, not a promise
These worked panel ratings and targets illustrate the formula with no extra derate. The 4.9 sun-hours come from NREL’s Colorado horizontal example; 2 sun-hours is a comparison input, not a city estimate.
| Worked inputs | Limited watts | Optimistic daily Wh |
|---|---|---|
| 400 W panel, 400 W cap, 4.9 sun-hours | min(400, 400) = 400 W | 400 × 4.9 = 1,960 Wh |
| 400 W panel, 400 W cap, 2 sun-hours | min(400, 400) = 400 W | 400 × 2 = 800 Wh |
| 600 W panel, 400 W cap, 4.9 sun-hours | min(600, 400) = 400 W | 400 × 4.9 = 1,960 Wh, not 2,940 Wh |
For a 1000 Wh battery target and a panel that can reach the 400 W cap, ideal peak sun hours = target Wh ÷ min(panel W, cap W): 1000 ÷ 400 = 2.5 sun-hours, with no conversion loss. The target is energy you want to add, not necessarily the pack’s full nameplate capacity.
No efficiency factor is silently applied. If you want a conservative energy need, you can raise the target. The calculator does not estimate your conversion loss or the loads you run while charging.
A sun-hour is not an hour on the clock
NREL FY24OSTI-90210 describes peak irradiance as about 1 kW/m². A location’s daily kWh/m² is sometimes called a sun-hour: it expresses the day’s solar energy as equivalent hours at that irradiance, not clock hours of sunshine.
The official Colorado horizontal example is 4.9 kWh/m²/day. It illustrates the unit. It is not a forecast for your city, a tilted portable panel, or your next outage day.
Use NREL’s PVWatts to look up your own plane-of-array solar-radiation figure with your location, tilt, and azimuth. Enter that peak sun-hour figure here, not PVWatts’ system-output kWh. This calculator does not call the PVWatts API or fetch a local forecast. The solar recharge guide explains the same method and its limits.
The station cap can be the bottleneck
If panel watts exceed the station’s solar-input cap, the cap is the limit. A larger panel nameplate does not all pass through a smaller charge controller. This simple model caps the watts before multiplying by sun hours; it does not model a charging curve or changing output through the day.
The estimate ignores soiling, shade, poor tilt, temperature, cable loss, and imperfect aiming. Real days are often lower. Weather and shade can reduce the day’s input to zero. Battery charging behavior can also limit how much energy is stored.
Published watt limits are not connection approval. Read your station’s regional manual for voltage and current windows, connectors, polarity, and panel-wiring rules. The source notes in the optional selector identify the published cap, not a tested panel-and-station pairing.
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Sources for sun hours and station caps
- NREL FY24OSTI-90210: peak irradiance about 1 kW/m², daily kWh/m² as sun-hours, and the Colorado horizontal 4.9 illustration.
- NREL PVWatts Calculator: look up a plane-of-array figure for your own location and panel orientation.
- Jackery Explorer 1000 V2 basic information: 400 W published solar-input maximum. Published solar-input maximum; 16–60 V window in Jackery materials.
- EcoFlow DELTA 2 US product page: 500 W published solar-input maximum.
- BLUETTI AC180 US product page: 500 W published solar-input maximum. Published 12–60 V solar-input window on the US page.
- Anker SOLIX C1000 US product page: 600 W published solar-input maximum.
Plan the energy you need to replace
- How much solar to recharge a power station in a day: panel ratings, sun hours, and connection limits.
- What a 1000 Wh power station can run during an outage: stored energy and the next recharge.
- Battery runtime calculator: estimate runtime or the battery Wh needed for a target duration.
- Refrigerator runtime guide: average energy use versus compressor starts.
Frequently asked questions
Can a 400 W panel recharge a 1000 Wh power station in a day?
With a station cap of at least 400 W and 4.9 peak sun hours, the optimistic ceiling is 400 × 4.9 = 1,960 Wh. At 2 sun-hours it is 400 × 2 = 800 Wh, already below 1000 Wh. The 4.9 figure is NREL’s Colorado horizontal illustration, not your forecast. Conversion losses, weather, shade, and placement can prevent a full recharge even when the ceiling exceeds the battery target.
Will a 600 W panel charge faster through a 400 W solar-input cap?
The station’s 400 W cap is the limit in this calculation: min(600, 400) × 4.9 = 1,960 Wh, not 2,940 Wh. This simple ceiling does not model changes in panel output during the day. Enough watts also do not prove electrical compatibility. Check the maker’s voltage, current, connector, and polarity limits before connecting panels.
Does 2.5 sun-hours mean my battery will be full in 2.5 clock hours?
No. For a 1000 Wh target at a limited input of 400 W, 1000 ÷ 400 = 2.5 ideal sun-hours with no conversion loss. Peak sun hours express solar energy relative to about 1 kW/m², not elapsed hours of sunshine. Actual input changes through the day, and charging losses and charge limits can lengthen the time. Use your own plane-of-array figure from PVWatts, not the optional Colorado example as a local forecast.