Calculator Inputs
Enter panel, battery, and load values. The form uses a three-column layout on large screens, two on smaller screens, and one on mobile.
Example Data Table
This sample shows how panel power, battery storage, and daily load can be compared using practical losses and usable capacity assumptions.
| Scenario | Panel Setup | Sun Hours | Battery Bank | Daily Load | Net Solar per Day | Usable Battery |
|---|---|---|---|---|---|---|
| Cabin Backup | 4 × 450 W | 5.5 | 24 V, 2 strings of 200 Ah | 3,000 Wh | 8,078 Wh | 8,208 Wh |
| Small Office | 8 × 550 W | 5.0 | 48 V, 2 strings of 100 Ah | 6,500 Wh | 17,952 Wh | 8,640 Wh |
| Weekend Shed | 2 × 300 W | 4.8 | 12 V, 2 strings of 150 Ah | 900 Wh | 2,203 Wh | 3,078 Wh |
Formula Used
Net Solar Wh/day = Panel Wattage × Panel Count × Peak Sun Hours × Controller Efficiency × Performance Ratio × (1 − System Losses)
Series Count = System Voltage ÷ Battery Unit Voltage
Parallel Strings = Battery Units ÷ Series Count
Nominal Battery Wh = System Voltage × Battery Unit Ah × Parallel Strings
Usable Battery Wh = Nominal Battery Wh × Depth of Discharge × Battery Efficiency
Required Stored Wh = Daily Load Wh × Backup Days × (1 + Reserve Margin)
Required Bank Ah = Required Stored Wh ÷ (System Voltage × Depth of Discharge × Battery Efficiency)
Required Array W = Required Stored Wh ÷ (Peak Sun Hours × Controller Efficiency × Performance Ratio × (1 − System Losses))
Recommended Panels = Required Array W ÷ Panel Wattage
Recharge Hours = Energy Needed to Raise SOC ÷ Net Charge Power
This estimate assumes the array charges the battery directly without additional daytime load consumption.
How to Use This Calculator
- Enter your panel wattage, panel count, and average peak sun hours for the installation location.
- Adjust controller efficiency, performance ratio, and system losses to match realistic site conditions.
- Set the battery system voltage, unit voltage, unit amp-hours, and the number of batteries you already own.
- Choose a battery chemistry. The calculator can apply common defaults, or you can keep custom efficiency values.
- Add your daily load, desired backup days, reserve margin, and charging SOC targets.
- Press Calculate. The results section will appear above the form and show coverage, storage, sizing, and recharge estimates.
- Use the CSV button to save the numeric results. Use the PDF button to create a compact report for planning or sharing.
FAQs
1. What does this calculator estimate?
It estimates daily solar production, usable battery energy, expected backup time, required battery capacity, recommended panel count, controller current, and recharge time between two battery charge states.
2. Why are efficiency and system losses important?
Real systems lose energy through controllers, temperature, wiring, inverter operation, and shading. Ignoring these factors can make a system look larger on paper than it performs in practice.
3. What is depth of discharge?
Depth of discharge is the usable share of stored energy. A 90% setting means only 90% of nominal battery energy is treated as available for service.
4. Why does the battery count depend on series strings?
Batteries must first be connected in series to reach system voltage. Only full series strings increase capacity in parallel, so incomplete sets are not counted in usable bank size.
5. Does recharge time include powering loads?
No. The recharge estimate assumes solar power is dedicated to charging the battery. If daytime appliances run at the same time, actual recharge time becomes longer.
6. Can I use this for lithium and lead acid batteries?
Yes. The chemistry selector applies common starting values for usable discharge and efficiency. You can still override both fields if your manufacturer specifications differ.
7. What if solar coverage is below 100%?
Coverage below 100% means the current array does not fully replace your daily energy use under the entered assumptions. Add more panel wattage, reduce load, or increase sun access.
8. Is this suitable for final engineering design?
It is strong for early sizing and scenario comparison. Final system design should still be checked against local climate data, cable sizing, inverter limits, and manufacturer charging requirements.