How to Size a Rooftop Solar System for Your Home
Installing rooftop solar is one of the smartest long-term investments an Indian homeowner can make. However, sizing a system too small will leave you with recurring electricity bills, while sizing it excessively large wastes capital without additional subsidy benefits.
This step-by-step guide explains how to calculate your total household electricity load, choose the right solar plant capacity (kW), and maximize your central subsidy under the PM Surya Ghar Muft Bijli Yojana.
30-Second Quick Takeaways
Essential steps for household load calculation and solar sizing
- Formula 1: Monthly Units Method: Divide your average monthly electricity bill consumption (kWh units) by 120. Example: 360 units / 120 = 3 kW Rooftop Solar System.
- Formula 2: Connected Load Method: List all daytime running appliances (ACs, fans, lights, fridge, pump), sum their running wattages, and add a 25% safety margin for peak surge.
- Solar Generation Benchmark: In India, each 1kW of rooftop solar with mono PERC or TOPCon bifacial panels produces 4.0 to 4.5 units (kWh) of clean power per sunny day (1,400–1,600 units per year).
- PM Surya Ghar Cap: Sizing up to 3kW maximizes the central subsidy cap (₹30,000 for 1kW, ₹60,000 for 2kW, and ₹78,000 for 3kW+), providing the highest return on investment.
Method 1: Sizing Solar Using Your Electricity Bill Units (kWh)
The simplest way to size your solar system is by looking at your average monthly consumption (units / kWh) on your DISCOM electricity bill:
| Average Monthly Bill Units (kWh) | Recommended Solar Size | Daily Solar Generation | PM Surya Ghar Subsidy |
|---|---|---|---|
| 120 – 150 Units / month | 1 kW System | 4.0 – 4.5 Units / day | ₹30,000 |
| 240 – 300 Units / month | 2 kW System | 8.0 – 9.0 Units / day | ₹60,000 |
| 360 – 450 Units / month | 3 kW System | 12.0 – 13.5 Units / day | ₹78,000 (Max Cap) |
| 600 – 800 Units / month | 5 kW System | 20.0 – 22.5 Units / day | ₹78,000 Cap |
Method 2: Sizing Solar Based on Appliance Wattages
List Daytime Appliances
Identify appliances running during daytime hours (10:00 AM – 4:00 PM): 1.5-Ton Inverter AC (~1,400W), Refrigerator (~250W), 4 Ceiling Fans (~300W), LED Lights (~100W), Water Pump (~750W).
Calculate Total Running Wattage
1,400W (AC) + 250W (Fridge) + 300W (Fans) + 100W (Lights) = 2,050 Watts running load.
Add Safety Margin & Inverter Efficiency
Add a 25% safety margin: 2,050W x 1.25 = 2,562W. Sizing a 3kW Rooftop Solar System perfectly covers this daytime load with surplus net-metered export credits!
⚡ Calculate Your 2026 Solar Savings & Subsidy
Select your monthly electricity bill to calculate the ideal system capacity, PM Surya Ghar subsidy, and lifetime savings:
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