Grid carbon intensity, explained for building design

What the number means

Carbon intensity divides the emissions from generating electricity by the electricity generated, so it depends on how much of the mix comes from fossil fuels. Ember, whose country data Our World in Data republishes, reports it in grams of CO₂-equivalent per kWh, covering all greenhouse gases converted to CO₂-equivalent over a 100-year horizon.

For a building, operational emissions from electricity are the kWh consumed multiplied by the intensity. For a heat pump, the emissions per kWh of heat delivered are roughly the grid intensity divided by its seasonal coefficient of performance, which is why the same heat pump has very different emissions on different grids.

Average versus marginal emissions

Average intensity spreads the emissions of the whole generation mix over all the electricity produced or consumed. Marginal intensity asks a different question: when demand changes, which generation changes with it, and what does that generation emit?

Short-run marginal rates treat the grid as fixed; long-run marginal rates also include the power plants that new demand causes to be built or retired. For long-lived changes such as electrification, Gagnon and colleagues (2022) argue that short-run marginal rates omit the new generation that added load induces: for US vehicle-electrification targets they estimated 286–336 kg/MWh with long-run marginal rates against 591 kg/MWh with a short-run rate, because in the US new load often leads to more wind and solar being built. Average, location-based figures are the usual basis for emissions reporting; marginal figures are useful for decisions about adding or shifting load.

Lifecycle versus direct emissions

Direct, or operational, factors count only what a power plant emits while running, mostly from burning fuel. Lifecycle factors add the emissions from building the plant, extracting and transporting fuel and disposing of the plant at the end of its life, so every source, including wind, solar, hydro and nuclear, has a value above zero.

Ember's figures aim to cover the full lifecycle, including upstream methane, supply chain and manufacturing emissions. For several sources it uses the IPCC's midpoint lifecycle values, for example 48 gCO₂e/kWh for solar and 24 gCO₂e/kWh for hydro. Ember notes that methane emissions from gas and coal supply are highly uncertain. Always check which basis a figure uses before comparing it with another source.

Where the data comes from

• Ember: free yearly electricity data for 215 countries from 2000, with generation by source and lifecycle emissions, under a CC BY 4.0 licence.
• Our World in Data: republishes Ember's lifecycle carbon intensity of electricity generation by country, with a time series from 1990, as charts and downloads.
• Electricity Maps: grid-zone data at 5-minute, 15-minute and hourly resolution, consumption-based (it traces flows between interconnected grids), with both lifecycle and direct emission factors.
• IEA: CO₂ emission factors from electricity and heat generation for countries worldwide since 1990, sold under licence, with a separate IEA database of life-cycle upstream emission factors for electricity (150 countries from 2015).
• US EPA eGRID: generation and emissions data for most US power plants, which some providers use for regional factors.

Why it matters for electrification and PV

The lower the grid's intensity, the lower the operational emissions of an all-electric building and the stronger the carbon case for replacing fuel boilers with heat pumps. On a high-intensity grid, every kWh saved avoids more emissions.

For on-site PV, the carbon benefit of each kWh depends on the grid electricity it displaces. The national average is the simple, common reference; hourly or marginal data give a better picture when the timing of generation matters. PV's own lifecycle footprint, 48 gCO₂e/kWh in the IPCC midpoint Ember uses, is small compared with the 700 gCO₂e/kWh Ember applies to its 'other fossil' category. Intensities change from year to year as grids add renewables or retire plants, so for buildings expected to last decades, look at the trend as well as the latest year.

How C4B shows grid carbon intensity

C4B shows the carbon intensity of the national electricity grid for the location you search, benchmarks it against other countries and shows the generation mix by fuel, using yearly country data from Our World in Data and Ember. The figures are national, not regional, so they do not capture differences between grid regions within a country.