Calculate how many solar panels you need for a home, cabin, or RV based on daily kWh, panel wattage, and regional peak sun hours.
ℹ️ Note: Includes 15% weather safety derating to protect battery reserves during partly cloudy conditions.
The Solar Panel Calculator determines the total photovoltaic (PV) array wattage and panel count required to supply your daily household electricity consumption (kWh) based on geographic Peak Sun Hours (PSH).
Peak Sun Hours does not measure hours of daylight; it measures the cumulative solar irradiance equivalent to 1,000 Watts per square meter hitting the Earth's surface. A sunny summer day might provide 6.0 PSH, while an overcast winter day may provide only 2.0 PSH.
Our sizing algorithm applies real-world environmental derating factors—including high-temperature coefficient losses, inverter DC-to-AC conversion losses, soiling, and MPPT tracking efficiency (82% net yield)—plus a recommended 15% safety buffer.
An off-grid home in Colorado with 4.8 average peak sun hours needs to generate 4,000 Watt-hours (4 kWh) per day using standard 400W commercial solar panels.
Effective Yield = 4.8 PSH × 0.82 Net Yield = 3.936 Wh per Watt of solar installed
Each installed Watt of solar panel capacity generates approximately 3.94 Watt-hours of usable energy daily.
Raw Array Watts = 4,000 Wh ÷ 3.936 = 1,016 Watts
Applying our 15% safety factor for seasonal variation: 1,016W × 1.15 = 1,168 Watts.
Panel Count = 1,168W ÷ 400W = 2.92 Panels → Round up to 3 Panels (1,200W)
Three 400W panels wired in series provide 1,200W total capacity, generating 4.7 kWh daily.
✅ Engineering Sizing Result: A 1,200W array of three 400W panels comfortably fulfills the 4 kWh daily demand with a 17% energy surplus.
Derives total panel array nameplate wattage necessary to offset total daily kilowatt-hour demand.
Always rounded up to the next integer to prevent undercharging batteries.
| Daily Load | Array Watts | 400W Panels | 300W Panels | Estimated Daily kWh Yield |
|---|---|---|---|---|
| 1 kWh / day | 400 Watts | 1 Panel | 2 Panels | 1.48 kWh / day |
| 3 kWh / day | 1,200 Watts | 3 Panels | 4 Panels | 4.43 kWh / day |
| 5 kWh / day | 1,600 Watts | 4 Panels | 6 Panels | 5.9 kWh / day |
| 10 kWh / day | 3,200 Watts | 8 Panels | 11 Panels | 11.81 kWh / day |
| 15 kWh / day | 4,800 Watts | 12 Panels | 16 Panels | 17.71 kWh / day |
Sunshine hours measures how long the sun is visible in the sky. Peak Sun Hours (PSH) measures the cumulative intensity of solar radiation equivalent to 1,000 W/m² (standard test conditions). A 12-hour summer day typically yields 5 to 6 Peak Sun Hours.
Yes, but output drops to 10% to 25% of their rated nameplate capacity depending on cloud density. That is why off-grid solar designs incorporate a battery autonomy reserve of 2 to 3 days.
Wiring panels in series increases array voltage while keeping amperage low, which allows thinner wire and reduces resistance. When paired with an MPPT charge controller, high-voltage series strings operate far more efficiently.
