Charging time
2hours
Full-sun-equivalent hours needed to reach the target.
Solar Panel Charging Time Calculator
Estimate how long solar panels may take to charge a battery or portable power station from one charge level to another.
This tool converts the needed battery energy into full-sun-equivalent charging hours, then estimates calendar days using peak sun hours. Weather, shade, panel angle, heat, wiring, controller behavior, and battery limits can all change the real result.
Solar charging inputs
Wh
Use the rated capacity of the battery or portable power station.
%
The current state of charge before solar charging starts.
%
Must be higher than the current charge.
W
Rated watts for each panel.
Enter the count of identical panels in the array.
%
Accounts for real-world panel and charging losses.
hours
Equivalent full-output sun hours per day.
Results
Estimated time
0.5days
Using 4 peak sun hours per day.
Energy needed
600Wh
Effective solar output
300W
Calculation breakdown
| Item | Value | Notes |
|---|---|---|
| Charge increase | 60% | 80% target - 20% current. |
| Energy needed | 600 Wh | 1,000 Wh battery x charge increase. |
| Effective solar output | 300 W | Panel watts, panel count, and system efficiency applied. |
| Charging hours | 2 hours | 600 Wh / 300 W effective output. |
| Calendar days | 0.5 days | 4 peak sun hours per day. |
Formula
chargingHours = capacityWh x ((targetPercent - currentPercent) / 100) / (panelWatts x panelCount x systemEfficiencyPercent / 100)The calculator rejects a target charge that is less than or equal to the current charge, because no charging time is needed in that case. Estimated days are charging hours divided by peak sun hours per day.
- capacityWh
- The battery capacity in watt-hours.
- targetPercent
- The desired state of charge.
- currentPercent
- The current state of charge.
- panelWatts
- Rated watts for each solar panel.
- panelCount
- Number of identical panels used for charging.
Example
Real charging can take longer if the panels are shaded, hot, poorly angled, or limited by the charge controller or battery input rating.
- Battery capacity is 1,000 Wh.
- Current charge is 20% and target charge is 80%, so the battery needs 60% of capacity.
- Energy needed is 600 Wh.
- Two 200 W panels at 75% system efficiency provide 300 W effective output.
- 600 Wh divided by 300 W gives 2 full-sun-equivalent charging hours.
- At 4 peak sun hours per day, that is about 0.5 days of good solar conditions.
How to use this calculator
- Enter the battery capacity in watt-hours.
- Enter the current and target charge percentages.
- Enter panel watts and number of panels.
- Adjust system efficiency and peak sun hours for the site and season when you have better data.
Input guide
- Battery capacity: total rated energy storage in watt-hours.
- Current charge and target charge: the start and end state of charge used to calculate energy needed.
- Solar panel watts: label rating for one panel, before real-world losses.
- System efficiency: estimated losses from panel conditions, wiring, controller, and charging behavior.
- Peak sun hours: equivalent daily hours at full rated solar intensity.
Common mistakes
- Entering a target charge equal to or below the current charge.
- Assuming panels produce their label watts all day.
- Ignoring shade, panel angle, heat, and seasonal sun changes.
- Forgetting that a power station may have a maximum solar input rating below the panel array rating.
Limitations
The formula uses a single efficiency value and average peak sun hours. It does not model clouds, moving shade, temperature derating, panel orientation, MPPT behavior, cable loss, battery tapering near full charge, or manufacturer input limits.
FAQ
What are peak sun hours?
Peak sun hours convert a day of changing sunlight into equivalent hours at full rated solar output.
Why include system efficiency?
Panels rarely deliver label watts continuously. Efficiency accounts for common losses between panel output and stored battery energy.
Why must target charge be higher than current charge?
Charging time is only meaningful when the battery needs additional energy. If the target is equal to or below the current charge, the calculator returns an input error.
Can I use this for portable power stations?
Yes, when you know the battery capacity, solar input limit, panel watts, and a reasonable efficiency estimate. Also check the manufacturer solar input limit.
Related calculators
Use these tools to compare solar recharge time with battery runtime and larger backup plans.
- Portable Power Station Runtime CalculatorEstimate how long a portable power station can run a load after efficiency losses and reserve.
- RV / Camping Power CalculatorEstimate daily campsite energy use, trip battery needs, and optional solar recharge.
- Home Outage Backup PlannerPlan 24, 48, or 72 hour backup needs for critical home loads using battery and generator estimates.
Methodology and disclaimer
Solar charging estimates vary with weather, shading, panel angle, temperature, charge controller behavior, cable losses, and battery limits.
The calculator finds the watt-hours needed between the current and target charge levels, divides by effective solar output, then divides full-sun-equivalent hours by peak sun hours per day.