Solar Panel Sizing Calculator

The Solar Panel Sizing Calculator estimates how large a solar system you need to cover your home's electricity use, based on where you live and how much power you consume. Enter your zip code, monthly kWh usage, panel wattage, and how much of your electricity bill you want to offset to get your required system size in kW. Secondary outputs include number of panels needed, daily and annual energy generation, and your monthly energy offset.

Used to determine average sun hours in your area

kWh

Check your electricity bill for average monthly usage

watts

Typical residential panels range from 300-500 watts

Accounts for inverter losses, wiring, and environmental factors

hours

Peak sun hours per day in your area (winter average)

Results

Required System Size

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Number of Panels Needed

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Daily Energy Generation

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Annual Energy Generation

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Monthly Energy Offset

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Frequently Asked Questions

How many sun hours per day do I get in my area?

Sun hours vary by location and season. Most areas in the US receive 4-6 peak sun hours daily. Winter months typically have fewer sun hours, so it's important to size your system based on the darkest months for year-round reliability.

What solar panel wattage should I choose?

Modern residential solar panels typically range from 300-500 watts. Higher wattage panels mean fewer total panels needed, but they may cost more per panel. 400W panels offer a good balance of efficiency and cost.

How do I calculate my monthly kWh usage?

Check your electricity bill for your monthly kWh consumption. Look for a 12-month average to account for seasonal variations. Most homes use between 600-1200 kWh per month.

What are system losses and why do they matter?

System losses account for energy lost through inverters, wiring, shading, and weather conditions. Typical losses range from 12-18%. These losses reduce your actual energy production below the theoretical maximum.

Should I size my system to offset 100% of my electricity usage?

Most homeowners aim for 100% offset, but you can choose based on your budget and goals. Some prefer 75-90% offset to minimize costs, while others choose 110-125% to account for future increases in usage or to sell excess power back to the grid.

How much roof space will I need for my solar panels?

Each panel typically requires about 15-20 square feet including spacing. A typical residential system needs 300-600 square feet of roof space, depending on system size and panel efficiency.

Can I use this calculator for off-grid systems?

Yes, this calculator works for both grid-tied and off-grid systems. For off-grid applications, consider sizing your system 25-50% larger to account for battery storage inefficiencies and cloudy weather periods.

What if my energy usage changes after installing solar?

Many homeowners increase their energy usage after going solar (electric vehicles, heat pumps, etc.). Consider your future energy needs when sizing your system, or plan for a system that can be expanded later.