How Much Rooftop Solar Does My Home Need? (Engineering Sizing Guide)

When homeowners decide to install solar, the most frequent mistake is accepting a generic "3 kW package" without checking their actual electricity consumption profile. Sizing rooftop solar is not an arbitrary choice; it is calculated using straightforward electrical physics and local solar irradiance.

Step 1: Determine Your Monthly Unit Consumption

Locate your recent electricity bills from the past 12 months. Look specifically for the Units Consumed (kWh) rather than the final rupee amount, as seasonal tariff slabs can distort unit counts.

Step 2: Calculate Required Capacity (kW)

Divide your average monthly units by 125:

• 250 units/month: Requires ~2 kW solar system
• 380 units/month: Requires ~3 kW solar system
• 600 units/month: Requires ~5 kW solar system
• 1200 units/month: Requires ~10 kW solar system

Step 3: Measure Shadow-Free Roof Space

Modern monocrystalline half-cut solar panels (540W–550W) require approximately 80 to 100 square feet of completely unshaded roof area per kilowatt.

A 3 kW system therefore requires 240–300 sq. ft. of clear south-facing or flat terrace space. Make sure to account for parapet wall shadows, overhead water tanks, and surrounding trees.

Step 4: Check Your Sanctioned Load

Utility distribution companies (such as MSEDCL) restrict the maximum solar capacity that can be connected under net metering to your sanctioned electrical load. If your current sanctioned load is 3 kW but your consumption warrants 5 kW, an application for a load enhancement must be submitted alongside the solar interconnection request.