Roof Solar Panel Calculator
Use this calculator to estimate the number of solar panels you might need, the potential energy production, and the approximate cost for a solar system on your roof. Input your average electricity usage, roof dimensions, and panel specifications to get a personalized estimate.
Typical US household uses 800-1000 kWh/month.
Varies by location (e.g., 4-5 hours in many US regions).
Common panel sizes range from 300W to 450W+.
Typical panel dimensions are around 68×40 inches.
Typical panel dimensions are around 68×40 inches.
Estimate the clear, unshaded area on your roof suitable for panels.
Accounts for real-world losses (e.g., temperature, wiring, dust). 75-85% is common.
National average is around $2.50 – $3.50 per watt before incentives.
Check your electricity bill for your average rate.
Solar System Estimate:
Panels Needed for Energy:
Max Panels Fit on Roof:
Recommended Panels:
Total System Size: kW
Estimated Daily Production: kWh
Estimated Monthly Production: kWh
Estimated Annual Production: kWh
% of Monthly Energy Needs Met: %
Estimated System Cost (before incentives):
Estimated Monthly Savings:
Estimated Annual Savings:
Understanding Your Roof Solar Panel Potential
Installing solar panels on your roof is a significant investment that can lead to substantial energy savings and environmental benefits. This calculator helps you get a preliminary estimate of what a solar system might look like for your home.
How the Calculator Works:
The calculator takes several key factors into account to provide an estimate:
- Average Monthly Electricity Usage (kWh): This is the most crucial input, as it determines how much energy your solar system needs to generate to offset your consumption. You can find this on your electricity bill.
- Average Daily Peak Sun Hours: This represents the equivalent hours per day when sunlight intensity averages 1,000 watts per square meter. It's a measure of your location's solar resource. Areas with more peak sun hours will generate more electricity from the same size system.
- Individual Solar Panel Wattage: This is the power output rating of a single solar panel under standard test conditions. Higher wattage panels can generate more electricity per panel.
- Individual Panel Dimensions (Length & Width): These inputs are used to calculate the area of a single panel, which then helps determine how many panels can physically fit on your usable roof space.
- Usable Roof Area for Panels (sq ft): Not all of your roof may be suitable for solar. Factors like shading from trees or chimneys, vents, skylights, and local setback requirements can reduce the usable area. This input allows you to specify the actual space available.
- System Derate Factor (%): Solar panels rarely perform at their absolute peak efficiency in real-world conditions. This factor accounts for various losses due to temperature, wiring resistance, dust, shading, and inverter efficiency. A typical derate factor ranges from 75% to 85%.
- Average Installed Cost per Watt ($): This is the average cost to purchase and install a solar system, usually expressed in dollars per watt. This figure can vary significantly based on location, installer, equipment quality, and system size.
- Current Electricity Cost ($/kWh): Your current electricity rate helps estimate your potential monthly and annual savings once your solar system is operational.
Key Outputs Explained:
- Panels Needed for Energy: This is the theoretical number of panels required to meet 100% of your average monthly electricity usage, based on your location's sun hours and panel specifications.
- Max Panels Fit on Roof: This is the maximum number of panels that can physically fit within the usable roof area you provided.
- Recommended Panels: This output takes the lower of the "Panels Needed for Energy" and "Max Panels Fit on Roof" to give you a realistic number of panels for your system.
- Total System Size (kW): This is the total power capacity of your recommended solar system, measured in kilowatts.
- Estimated Daily/Monthly/Annual Production (kWh): These figures represent the expected electricity generation from your recommended system, taking into account the derate factor.
- % of Monthly Energy Needs Met: This shows what percentage of your average monthly electricity consumption your solar system is expected to cover.
- Estimated System Cost (before incentives): This is a rough estimate of the total cost of your solar system before any federal, state, or local incentives (like tax credits or rebates) are applied.
- Estimated Monthly/Annual Savings: These figures represent the approximate amount you could save on your electricity bill by generating your own power.
Important Considerations:
This calculator provides an estimate and should not be considered a final quote. Many factors can influence the actual performance and cost of a solar system, including:
- Shading: Even minor shading can significantly reduce panel output.
- Roof Angle and Orientation: South-facing roofs (in the Northern Hemisphere) with an optimal tilt generally produce the most power.
- Local Regulations: Building codes, HOA rules, and utility interconnection requirements can affect your installation.
- Incentives: Federal tax credits, state rebates, and local programs can drastically reduce the net cost of a solar system.
- Battery Storage: This calculator focuses on grid-tied systems. Adding battery storage would increase costs but provide energy resilience.
For an accurate assessment and detailed quote, it's always recommended to consult with multiple local solar installers who can perform a site-specific evaluation.