Solar Panel Calculator
Determine the ideal rooftop solar PV system capacity (kW) and number of solar panels required to offset your home electricity bill.
Calculator Inputs
LiveHow to use the Solar Panel Calculator
- 1Enter your average monthly electricity consumption in kWh (or check your utility bill).
- 2Enter average peak sun hours per day in your region (typically 4.5 to 5.5 hours).
- 3Select solar panel wattage rating (e.g. 450W or 540W modern panels).
- 4View recommended system capacity in kW, number of panels needed, and required roof area.
How Solar Panel is Calculated
Daily energy consumption target is divided by regional peak sun hours and adjusted for system derate efficiency losses (typically 80%) to determine necessary DC kW capacity.
The 0.80 derating factor accounts for inverter conversion losses, wiring losses, panel dust, and temperature heat coefficients.
- 1Daily target = 450 / 30 = 15 kWh/day
- 2System kW = 15 / (5 × 0.80) = 3.75 kW system
- 3Number of Panels = (3.75 × 1,000) / 450 = 8.33 -> 9 panels (4.05 kW actual)
- 4Estimated roof area needed = 9 panels × ~22 sq ft = ~200-250 sq ft
What affects Solar Panel results
- Roof orientation (south-facing in Northern hemisphere yields maximum annual output) and tilt angle.
- Shadows from nearby trees, parapet walls, or neighboring buildings.
- Seasonal daylight variation between summer and winter.
Frequently Asked Questions
What are Peak Sun Hours?
Peak sun hours represent the equivalent number of hours per day when solar irradiance averages 1,000 Watts per square meter, usually between 4 and 6 hours in sunny climates.
How much roof space do solar panels need?
Modern monocrystalline solar panels typically require approximately 60 to 70 square feet of unobstructed roof space per 1 kW of installed capacity.
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