Home Solar System Size Calculator (kW and Panels)
Enter your electricity use and sun hours to estimate the solar system size you need.
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Home Solar System Size Calculator (kW and Panels) by TheCalcTools
How the Home Solar System Size Calculator (kW and Panels) works
A 1 kW solar array produces about 1 kWh for every peak sun hour, less system losses. Divide the daily energy you want by peak sun hours and the performance ratio to get the kW you need.
Peak sun hours depend strongly on location and season: often 4 to 6 in South Asia, the Middle East and the southern US, 2.5 to 3.5 in northern Europe. Use a local figure.
The formula
Worked example
Using the default values shown in the calculator:
| Electricity use per month (kWh) | 600 |
|---|---|
| Peak sun hours per day (your location) | 5 |
| Share of use to cover | 100 % |
| System performance ratio | 80 % |
| Panel rating (W) | 550 |
| Area per panel (m²) | 2.6 |
| Installed cost per watt | $0.6 |
- 600 kWh a month = 4.93 kW needed at 5 sun hours and 80%.
- That is 9 panels of 550 W, about 23 m² of roof.
Result:
| System size needed (kW) | 4.93 |
|---|---|
| Number of panels | 9 |
| Roof area (m²) | 23.4 |
| Yearly production (kWh) | 7,227 |
| Estimated installed cost | $2,970 |
Frequently asked questions
How many panels do I need for 600 kWh a month?
At 5 peak sun hours and 80% performance, about 4.9 kW, or 9 panels of 550 W.
Sources and further reading
- NREL: PVWatts calculator documentation
- World Bank / Solargis: Global Solar Atlas
- Wikipedia: Photovoltaic system
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.