02What's flowing through the wires?
How clean each hour of power is
How much CO₂ does each kilowatt-hour of electricity carry, and when in the day is it cleanest?
How dirty a kilowatt-hour is depends on where and when it is made. Over the 12 months to 14 October 2026, the average carbon intensity, estimated from each hour's generation mix with lifecycle emission factors per fuel, ran from about 35 grams of CO₂ per kWh in France to about 549 in Poland; Germany averaged about 307.
What a gram of CO₂ per kilowatt-hour describes
Carbon intensity is the emissions carried by each unit of electricity, written gCO₂/kWh. The figures here count emissions where the power is generated (production-based): for every hour, the generation from each fuel in the zone is multiplied by a standard emission factor for that fuel, and the results are added and divided by the total. The factors are lifecycle values from the IPCC's fifth assessment report, so they include building the plant, mining and transporting the fuel, and decommissioning, and they apply to wind, solar, hydro and nuclear as well as to gas and coal.
A standard factor per fuel is an average over many plants. A modern combined-cycle gas plant running at full output emits less per kilowatt-hour than an old one cycling up and down, and the two are treated alike here. This is a model of the hour, built from measured generation, and it will differ from plant-level metering by some margin in either direction.
Two charts answer two questions. The daily series shows how the mix has moved through the year: windy weeks and sunny months pull it down, a still cold week with coal and gas on the system pushes it up. The hourly profile shows the shape of an average day, cleanest around the solar peak and dirtiest through the evening ramp, which is why moving a flexible load into the middle of the day lowers its emissions without changing the amount of electricity it uses.
Production-based accounting describes the electricity generated inside a zone. Consumption-based accounting adjusts for trade, adding the emissions of imported power and removing those of exports, and it can give a materially different figure for a country that imports heavily. Both are legitimate and they answer different questions; mixing them across zones in one chart would be the error. Neither describes the tariff a household has signed, which is a contractual claim on particular generation and is settled in its own accounting. The comparison across zones here is about the physical grid at a given hour.
Questions
How much CO₂ does a kilowatt-hour of German electricity emit?
About 307 grams on average over the 12 months to 14 October 2026, an estimate from each hour's generation mix with lifecycle emission factors per fuel, which include building the plants. Among the zones compared, it ran from about 35 grams in France to about 549 in Poland.
What is carbon intensity?
The grams of CO₂ each kilowatt-hour carries, counted where it is generated and including the emissions from building the plant (lifecycle). It changes by the hour with the fuel mix: over the 12 months to 14 October 2026, Germany averaged about 307 grams per kWh, an estimate from its generation mix.
How these numbers are made: Production-based carbon intensity, Renewable share of generation.
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