Going Solar: How to Size a System and Estimate the Savings
A practical guide to home solar — understanding your usage, how many panels you need, sizing the inverter and battery, net metering, the payback period and the carbon you save.
Solar Panel Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Panels needed
5
- System size (kW)
- 2.00
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Solar Panel Calculator
The Solar Panel Calculator works out your panels needed, along with 1 related figure in an instant. Enter daily energy need, peak sun hours per day and panel wattage and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the daily energy need.
- Enter the peak sun hours per day.
- Enter the panel wattage.
- Read off your panels needed, together with system size (kw) — the calculator updates automatically, with no button to press.
Worked example
For example, with daily energy need of 10 kWh, peak sun hours per day of 5 hours and panel wattage of 400 W, the panels needed is 5.
| Daily energy need | 10 kWh |
|---|---|
| Peak sun hours per day | 5 hours |
| Panel wattage | 400 W |
| Panels needed | 5 |
|---|---|
| System size (kW) | 2.00 |
Results are estimates for educational use, not professional advice.
Frequently asked questions
Divide your daily energy in watt-hours by sun hours times panel wattage. For 10 kWh a day, 5 sun hours and 400 W panels, you need about 5 panels.
They are the equivalent hours of full-strength sunlight your location gets daily, typically 3–6 depending on region and season.
Yes. Panels degrade and systems have losses, so adding 20–25% more capacity is sensible for reliable supply.
No. This finds panel count for generation. Battery storage is sized separately based on how much backup you want.
Enter the daily energy need. Enter the peak sun hours per day. Enter the panel wattage. Read off your panels needed, together with system size (kw) — the calculator updates automatically, with no button to press.
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