Enter your system's annual kWh production and grid emissions factor to see CO2 avoided, in tons and tree-equivalents.
U.S. average grid factor is roughly 0.85 lb CO2/kWh (EPA eGRID); your state's actual factor varies with its generation mix.
Every kWh your panels produce is a kWh the grid didn't have to generate, mostly from fossil fuels depending on your region's mix. This converts your annual production, from the production calculator, into avoided emissions and two more intuitive equivalents.
The grid emissions factor is doing most of the work in this calculation, and it varies more by region than most people expect — the same solar system offsets meaningfully more CO2 in a coal-heavy grid region than in a hydro- or nuclear-heavy one, even with identical production.
States with more coal or gas generation have a higher factor than states with more hydro, nuclear, or existing renewables — a kWh saved in a coal-heavy state avoids more CO2 than the same kWh in a hydro-heavy one.
They're commonly used EPA-derived approximations meant for intuition, not precise accounting — a mature tree absorbs roughly 48 lb of CO2 per year and an average car emits about 0.9 lb per mile.
Your specific state or utility's factor gives a more accurate result if you can find it — a national average is a reasonable fallback, but regional generation mixes vary enough that it can meaningfully over- or understate your actual impact.