Solar Panel Charge Time Calculator
Instant solar panel charge time calculator: estimate peak-sun-days to recharge a battery bank from PV watts and PSH—not UPS runtime.
Quick answer
Charge days (PSH) ≈ Battery Wh ÷ (Array W × PSH × η). Example: 10,000 Wh, 2000 W array, 5 PSH, η 0.8 → ~1.25 sun-days. Size bank first in the solar battery bank calculator; enlarge array in the solar panel calculator if recharge is slow. Hub: Solar calculator.
Quick Charge Time Calculator
Defaults: 10,000 Wh · 2000 W array · PSH 5.0 · η 0.80.
10,000 ÷ (2000 × 5 × 0.8).
Advanced Charge Time Calculator
Charge Time Results
Engineering disclaimer
Planning estimate only. Assumes constant effective charge power during PSH—clouds and MPPT limits change real time. Not UPS runtime.
Sun-days by array W
| Array W | Sun-days |
|---|
People also ask
- How long to charge? Wh ÷ (W×PSH×η).
- How long to charge 100 Ah with solar? Convert Ah→Wh (× V), then same formula—e.g. 100 Ah × 12 V = 1,200 Wh.
- Clock hours? Roughly sun-days × daylight—not exact.
- UPS? Different intent—do not merge.
Planning guidance
This page estimates how many peak-sun-days PV needs to restore depleted battery energy. It is a PV storage recharge screen—not UPS charge time.
- PSH: Get site resource from peak sun hours.
- Autonomy context: battery autonomy days sizes how long the bank lasts; this page checks recharge speed.
- Array sizing: If recharge is slow, increase kW in panel sizing.
- MPPT: Charge-path efficiency includes controller losses—see MPPT sizing.
- Hub: Solar calculator.
Last updated: 2026-08-07. Assumes constant effective charge power during PSH—not UPS runtime.
Typical scenarios
- Overnight discharge: Restore usable Wh before next night (target < 1 sun-day).
- Multi-day recovery: After autonomy event, size array so recharge < 1–2 sun-days.
- Partial DoD: Only restore depleted Wh (e.g., 50% of 20 kWh bank = 10,000 Wh).
Charge time formula (aligned to this calculator)
Daily energy available for charging:
Daily charge energy (Wh) ≈ Array W × PSH × η
Time to restore depleted energy:
Sun-days = Battery Wh to restore ÷ (Array W × PSH × η)
In kWh terms: bank_kWh ÷ (array_kW × PSH × η) gives the same sun-days result. Rough clock hours ≈ sun-days × 24 (coarse—not constant-rate charging).
Bank method: how to size a solar battery bank (PV autonomy—not UPS).
Worked examples
| Case | Inputs | Sun-days |
|---|---|---|
| Default (calculator) | 10,000 Wh · 2000 W · 5 PSH · η 0.8 | 10,000 ÷ (2000×5×0.8) = 1.25 |
| 10 kWh bank, 50% DoD | 5,000 Wh · 1500 W · 4.5 PSH · η 0.8 | 5,000 ÷ (1500×4.5×0.8) ≈ 0.93 |
| Cloudy week recovery | 20,000 Wh · 3000 W · 3.0 PSH · η 0.75 | 20,000 ÷ (3000×3.0×0.75) ≈ 2.96 |
PV recharge vs UPS charge time
- This calculator: PV array → MPPT/charge controller → battery bank under peak sun hours resource assumptions.
- UPS charge time: AC mains or internal UPS charger → battery—different power path, different tools, different intent.
- Do not merge UPS runtime or UPS battery sizing workflows with this PV recharge screen.
Formula (quick reference)
Sun-days = Battery Wh ÷ (Array W × PSH × η)
Approx clock hours ≈ sun-days × 24 (coarse).
Formula and sources
Planning estimate only. Real recharge follows irradiance profile, MPPT limits, and battery BMS acceptance.
- NREL PVWatts — site PSH and daily energy estimates
- NREL System Advisor Model (SAM) — storage and PV coupled modeling
- How to size a solar battery bank (CalcPanel)
Frequently Asked Questions
How do I calculate solar panel charge time?
Sun-days = Wh ÷ (array W × PSH × η). Example: 10,000 Wh ÷ (2000 W × 5 PSH × 0.8) ≈ 1.25 sun-days.
How long to charge a 100 Ah battery with a solar panel?
Convert to Wh first: Wh = Ah × V (e.g. 100 Ah × 12 V = 1,200 Wh). Then sun-days = Wh ÷ (array W × PSH × η). Example: 1,200 ÷ (400 × 5 × 0.8) ≈ 0.75 sun-days. Use the Ah to Wh calculator if needed.
Is this the same as UPS charge time?
No—this is PV→battery recharge under solar resource assumptions. UPS charger runtime is a different domain—do not merge workflows.
What efficiency should I use?
Often 0.75–0.85 including MPPT, wiring, and battery acceptance. Confirm OEM charge profiles and BMS limits.
How do I convert sun-days to clock hours?
Rough estimate: clock hours ≈ sun-days × 24. Real recharge follows daylight and cloud cover—not a constant rate.
What if weather is cloudy?
Lower effective PSH lengthens recovery. Example: dropping PSH from 5.0 to 3.0 increases sun-days by ~67%.
How does this relate to battery autonomy?
Battery autonomy days sizes how long the bank lasts on stored energy; this page checks how fast PV recharges depleted Wh.
What if recharge is too slow?
Increase array kW in panel sizing, raise PSH with better tilt/site, or reduce autonomy depth / DoD.
What is the next step?
If recharge is slow, resize the array or review battery autonomy days for a balanced off-grid design.
Is this a solar panel charging calculator?
Yes for PV→battery recharge sun-days (array W × PSH × η vs battery Wh). It is not a UPS charger timer and not a shopping kit estimator. For bank energy first, use the solar battery bank calculator.
How do I calculate solar panel size for battery charging?
Rearrange the charge-time formula: needed array W ≈ Battery Wh ÷ (PSH × η × target sun-days). Example: 1,200 Wh ÷ (5 × 0.8 × 1 day) ≈ 300 W planning array. Or enter Wh / PSH / η here and raise array W until sun-days meet your recovery target—then confirm with panel sizing.
How long does it take a 25 W solar panel to charge a battery?
Example: 100 Ah × 12 V = 1,200 Wh at PSH 5.0 and η 0.80: sun-days = 1,200 ÷ (25 × 5 × 0.8) = 12 sun-days (~288 clock hours if you wrongly treat sun as continuous). A 25 W panel is trickle-class for that bank—use a larger array or a smaller battery for practical recovery.
How it works
Daily PV energy available for charging is array watts × PSH × efficiency. Dividing depleted Wh by that energy yields peak-sun-days to recover.