How to Size a Solar System
Going solar is one of the best investments a homeowner can make, but knowing what size system you need can be confusing. Our Solar Rooftop Calculator takes the guesswork out of the process. It calculates your required Kilowatt (kW) capacity based on your actual energy usage, local electricity rates, and average sunlight exposure.
If you are financing your solar installation with a home improvement loan, you can estimate your monthly payments using our EMI Loan Calculator to see if the solar savings outweigh the loan costs!
The Calculation Math
To find out what size system you need to cover 100% of your electricity bill, we reverse-engineer your daily usage.
- 1. Find Daily kWh: Divide your Monthly Bill by your Electricity Rate to get monthly kWh. Divide by 30 to get daily kWh.
- 2. Account for Sun Hours: A 1kW system produces 1kWh for every hour of direct sunlight. However, systems are not 100% efficient.
- 3. The Derate Factor: Inverters, wiring, and heat reduce efficiency. We apply an industry-standard 0.8 (80%) derate factor to the raw math to give you a realistic real-world system size.
Roof Space & Incentives
How much space do you need? On average, modern solar panels require about 70 square feet of unshaded roof space per 1 kW of installed capacity. If your roof is too small, you can use the "Calculate by Area" tab to see what your maximum generation potential is.
Federal Tax Credit (ITC): The U.S. government currently offers a 30% Investment Tax Credit for residential solar installations. This means you can deduct 30% of the gross installation cost directly from your federal taxes, drastically reducing your payback period. Learn more about Net Metering and grid-tied systems.