Choose U.S. or Metric units, enter your system, and pick a grid region below. Formula: Annual CO2 Offset = System Size × Peak Sun Hours × System Efficiency × 365 × Emission Factor.
Units
Your Solar System
Not sure what a field means? Tap the ⓘ next to its label.
The total nameplate DC rating of your solar array, in kilowatts — check your installer's proposal or a panel count × panel wattage. A typical U.S. home system is 6–10 kW.
kW
The average number of hours per day your location receives sunlight intense enough to count as 1,000 watts per square meter — it drives how much energy your system actually produces, not just daylight hours. Look yours up with the Solar Irradiance by ZIP Code tool.
hrs/day
Select the grid your solar system offsets electricity from. U.S. entries use EPA eGRID subregions (more accurate than the national average if you know yours); international entries use Ember's Global Electricity Review and UK DEFRA figures. Selecting a region auto-fills the Emission Factor field, which stays fully editable if you have a more exact figure from your utility.
The amount of CO2 released per kilowatt-hour of grid electricity your solar system displaces. Auto-fills from Grid Region above, but stays editable — enter your own figure if you know your utility's exact published rate or eGRID subregion value for a more accurate result.
lb/kWh
System Efficiency, System Life, Degradation, and Diesel Backup — every field has a sensible default and stays editable.
Advanced Options
The combined real-world losses between your panels' rated output and the electricity that actually reaches use — inverter conversion, wiring, soiling, and shading. 80% is a common planning default; well-maintained systems can reach the mid-80s.
%
How many years to project your Lifetime CO2 Offset over. 25 years is the standard solar panel warranty period and industry planning default.
yrs
Solar panels lose a small amount of output every year — typically 0.3–0.7% based on manufacturer warranty data. This calculator compounds that loss year over year for your Lifetime CO2 Offset, matching NREL's PVWatts-style methodology, rather than assuming flat output.
%/yr
For off-grid or hybrid systems: the share of your baseline energy that would otherwise come from a diesel generator instead of the grid. Diesel generation is typically dirtier per kWh than grid power, so this blends the Diesel Emission Factor in proportionally, raising your effective CO2 offset. Leave at 0% for a standard grid-tied system.
%
CO2 released per kilowatt-hour generated by a diesel generator — only used if Diesel Backup above is greater than 0%. Defaults to a typical mid-size genset figure (~0.4 L diesel per kWh at 2.68 kg CO2/L); check your generator's datasheet for an exact figure.
lb/kWh
Your Results
Annual CO2 Offset
—
US tons CO2
Lifetime CO2 Offset
—
US tons CO2
Annual Energy Production
—
kWh/year
Real-World Equivalents
Trees Planted is always shown. Toggle which of Cars Off Road or Miles Not Driven is featured — both are always calculated and listed below.
Trees Planted / Year
—
trees, EPA equivalent
Cars Off Road / Year
—
cars, EPA equivalent
Miles Not Driven / Year
—
miles/year not driven
Formula: —
Results are estimates for reference and planning purposes only and do not replace a licensed solar installer's site assessment.
🔗 Related Tools
📍 Don't know your Peak Sun Hours yet? Look them up with the Solar Irradiance by ZIP Code tool.
💰 Want to see dollar savings and payback period instead of CO2? Try the Solar Savings Calculator.
📐 Not sure what size system to enter? Start with the Solar Panel Size Calculator.
🔋 Sizing a full off-grid system, including diesel backup and battery bank? Use the Off-Grid System Sizing calculator.