Solar Panel Sizing: How Many Panels Do You Need?
A complete guide to calculating the right solar panel capacity for your home or off-grid system based on your energy consumption.
Understanding Your Energy Needs
Before sizing your solar system, you need to know your daily energy consumption in kilowatt-hours (kWh). List every appliance with its wattage and daily usage hours.
Step 1 — Calculate Daily kWh
Daily kWh = Σ (Appliance Watts × Daily Hours) ÷ 1000
Example: An AC (1500W × 8h) + fridge (150W × 24h) + 3 fans (75W × 8h each) = 12,000 + 3,600 + 1,800 = 17,400 Wh = 17.4 kWh/day
Step 2 — Account for System Inefficiency
Solar systems lose roughly 20% of energy to inverter inefficiency, wiring losses, and temperature derating. So use an efficiency factor of 0.8.
Step 3 — Determine Peak Sun Hours
Peak sun hours (PSH) is the number of hours per day your location receives sunlight equivalent to 1000 W/m². Most regions average 4–6 PSH. Check solar maps for your area.
Step 4 — Calculate Panel Capacity
Required panel watts = (Daily kWh × 1000) ÷ (PSH × 0.8)
For 17.4 kWh/day at 5 PSH: = 17,400 ÷ 4 = 4,350 W of panels
That's approximately 11 × 400W panels or 15 × 300W panels.
Use Our Solar Sizing Tool
Enter your appliances and usage in our solar panel sizing calculator and get an instant recommendation.