Solar Panel Calculator
Enter your electricity usage and location details to find out how many solar panels you need, total system size, estimated annual generation, and potential savings.
System Inputs
Results
Peak Sun Hours by Region
| Region | PSH/day | Examples |
|---|---|---|
| Excellent | 6–7 PSH | Arizona, UAE, Saudi Arabia, N. Australia |
| Very Good | 5–6 PSH | California, Spain, Italy, S. India, Texas |
| Good | 4–5 PSH | N. India, Brazil, S. Africa, Florida, Turkey |
| Moderate | 3–4 PSH | Central Europe, New York, China (avg), Japan |
| Low | 2–3 PSH | UK, Germany, Scandinavia, Canada (north) |
Frequently Asked Questions
The number depends on your monthly electricity consumption, your location's peak sun hours, and the wattage per panel. The formula is: Panels = Daily kWh ÷ (Panel kW × PSH × efficiency). A typical UK home needs 6–10 panels on a south-facing roof; a US home may need 20–30.
Peak sun hours (PSH) represent the number of hours per day where sunlight intensity averages 1,000 W/m². Arizona gets ~6.5 PSH; the UK gets ~2.8 PSH. Find your region's value using a solar irradiance map, or use our quick-fill buttons above.
System efficiency (performance ratio) accounts for inverter losses, heat, wiring, and soiling. Use 80% as a reliable default. Well-optimised systems with micro-inverters and minimal shading can reach 85–90%; systems with shading or older equipment may drop to 70–75%.
Savings = annual generation × self-consumption rate × electricity tariff. A 5 kW system generating 6,000 kWh/year, with 70% self-consumption at $0.20/kWh, saves ~$840/year. Adding a feed-in tariff for exported excess can increase savings further.
How the Solar Panel Calculator Works
This calculator uses a three-step method trusted by solar installers worldwide:
- Daily energy demand: Monthly kWh ÷ 30.44 days = daily kWh needed
- Per-panel daily output: Panel wattage (W) ÷ 1000 × Peak sun hours × System efficiency = kWh/day per panel
- Panels needed: Daily demand ÷ Per-panel daily output, rounded up to the nearest whole panel
Annual generation is calculated as: Panels × Panel kW × PSH × 365 × efficiency. Savings are based on the portion of generated electricity you self-consume (using the self-consumption rate) multiplied by your electricity tariff.
What Size Solar System Do I Need?
System size = Number of panels × Panel wattage. Common residential sizes:
- 3–4 kW: Small home, UK/Germany (~250–350 kWh/month)
- 5–6 kW: Medium home, Central Europe (~400–550 kWh/month)
- 8–10 kW: Large home or EV charging, sunny regions (~700–1,000 kWh/month)