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PV System Size Calculator
Determine the required PV system size to meet your energy consumption.
PV System Inputs
Required System Size
Solar Panels Needed
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Total Capacity
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Annual Production
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How to Size a Solar PV System
A PV system must generate enough energy to meet your daily load. Undersizing means grid dependence; oversizing wastes capital. The calculation considers your energy consumption, local sun availability, and system losses.
The Sizing Formula
Required System Size (kW) = Daily Energy (kWh) / (Peak Sun Hours × System Efficiency)
Number of Panels = (System Size kW × 1000) / Panel Wattage
Step-by-Step Sizing Process
- Calculate daily consumption: Sum all loads (watts) × usage hours = Wh/day. Add 20% buffer.
- Find peak sun hours: Use solar irradiance data for your location.
- Account for losses: Wire losses, inverter efficiency, temperature derating, soiling — typically 15–25%.
- Size the array: Divide daily energy by effective sun hours.
- Size the inverter: Match to peak array output.
- Size battery storage (if off-grid): Days of autonomy × daily consumption / DoD.
Practical Examples
Example — Off-grid cabin: Daily load 5kWh, 5 peak sun hours, 20% losses. System = 5 / (5 × 0.8) = 1.25 kW → 4 × 350W panels. Battery: 2 days autonomy, 50% DoD → 5 × 2 / 0.5 = 20kWh battery bank (e.g., 48V × 416Ah).
Example — Grid-tied home: 900kWh/month = 30kWh/day, 5.5 sun hours, 82% efficiency. System = 30 / (5.5 × 0.82) = 6.65kW → 17 × 400W panels.