Rooftop Solar Design Calculator (Excel Workbook) | kW Sizing, kWh Estimate, Savings & Payback (USA + Global)

Planning rooftop solar and want clear numbers before you commit? This Excel workbook helps you estimate the right solar system size (kWdc), expected 1st-year energy generation (kWh/year), electricity bill savings, and payback using practical assumptions.

Built USA-first, but flexible enough for India, Canada, and other regions using editable region presets (tariff, solar resource/PSH, losses, and economics assumptions).

What you can calculate
• Recommended system size (kWdc) based on your annual electricity use
• 1st-year energy estimate (kWh/year) + monthly breakdown
• Annual savings + simple payback
• Optional installer-grade checks: module/inverter selection, basic string sizing, spacing/shading planning, cable sizing and voltage drop directionally
• A clean Quote/Summary page for sharing

How to use (Quick Start)
1. Select your Region Preset
2. Enter annual kWh, tariff, and solar resource (PSH) in the Inputs sheet
3. Review Quick Results (kW, kWh/year, savings, payback)
4. Optional: choose module + inverter and run detailed checks for string sizing and layout

Full user manual
I’ve written a step-by-step guide here.

Compatibility: Microsoft Excel (recommended), Google Sheet or any spreadsheet application.

I’ve enabled a small launch discount on my Rooftop Solar Design Calculator (Excel Workbook). If you were waiting to try it, you can use this coupon:

Coupon code: SOLAR26

Note: This is a planning and estimation tool. Final design and installation should comply with local electrical codes and be validated by a qualified professional.