Solar Panel CO₂ Offset Calculator
Estimate the annual CO₂ your solar array offsets by displacing grid electricity.
How it works
kWh/yr = size (kW) × peak sun hours × 365 × performance ratio · CO₂ = kWh × grid factor
Solar panels cut emissions by replacing electricity you would otherwise buy from the grid, so the offset is the energy generated multiplied by the grid’s carbon intensity. Annual generation is the system size times daily peak-sun hours times 365, reduced by a performance ratio (typically 75–85%) that captures inverter, heat and dust losses. The dirtier the grid you displace, the larger the offset per kWh.
Worked example
A 5 kW system with 4.5 peak-sun hours a day at an 80% performance ratio makes 5 × 4.5 × 365 × 0.80 ≈ 6,570 kWh a year. On a 0.4 kg/kWh grid that offsets about 2,628 kg — roughly 2.6 tonnes of CO₂ each year.
Sources: NREL — PVWatts Calculator
Frequently asked questions
What are peak sun hours?
Peak sun hours are the equivalent number of hours per day at full 1,000 W/m² sunshine. It bundles the whole day’s variable sunlight into one figure — typically 3–6 depending on location and season.
Why apply a performance ratio?
A panel’s nameplate rating is a lab figure. In the field, inverter losses, wiring, heat, shading and dust cut output, so real systems deliver about 75–85% of the theoretical maximum.
Does the offset shrink as grids get cleaner?
Yes. As the grid adds renewables its carbon intensity falls, so each solar kWh displaces less CO₂ over time — though your generation stays the same.
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This calculator is for educational purposes. Double-check important results before acting on them.