Solar Panel Calculator
Tools you might need next
Calculate solar battery bank capacity in kWh for off-grid or backup power from daily load, autonomy days, depth of discharge, and inverter efficiency.
Calculate wind turbine power output in watts from rotor diameter, wind speed, air density, and turbine efficiency using the Betz limit formula.
Calculate optimal solar panel tilt angle from latitude, roof pitch, and season. Find year-round, summer, and winter angles for maximum energy harvest.
Convert monthly kWh usage to average daily demand. Account for seasonal variation — summer AC loads may exceed the annual average by 30–50%.
Daily kWh = Monthly kWh / 30Divide daily demand by peak sun hours for your location and apply orientation/tilt factors. South-facing at optimal tilt receives 100%; east/west arrays lose 10–20%.
Array kW = Daily kWh / (Peak sun hours × Orientation factor × System efficiency)Divide required array wattage by individual panel rating. Round up and verify total roof area accommodates panel dimensions plus required setbacks.
Panel count = Array watts / Panel wattageUpdated: July 2026
900 kWh/month = 30 kWh/day. At 6.5 peak sun hours and 85% system efficiency, need ~5.4 kW array. Fourteen 400W panels (5.6 kW) cover usage with modest surplus.
600 kWh/month = 20 kWh/day. At 4.2 peak sun hours, need ~5.6 kW. A 6 kW system (15 × 400W panels) offsets ~95% of annual usage despite lower sun hours.
Only 280 sq ft available fits eight 400W panels (3.2 kW). At 5 peak sun hours, produces ~13 kWh/day — offsetting roughly half of a 800 kWh/month household.
Real-world output is 75–85% of nameplate due to inverter losses, wiring, soiling, temperature derating, and shading. Always apply a 0.80–0.85 system efficiency factor.
Annual kWh averages account for winter heating loads and shorter days. Sizing from July bills alone undersizes the array for year-round offset.
Sizing a solar array correctly balances upfront cost against energy production. This calculator estimates how many panels you need from monthly electricity usage, local peak sun hours, panel wattage, roof orientation, and system derating factors.