Marginal Emissions Rate
The CO2 emissions rate of the next power plant that would turn on (or off) in response to a change in demand. Often higher than the average grid emissions factor because peaker plants are usually gas-fired.
Why It Matters
When you reduce usage or export solar, you displace the marginal generator — not the average. This means evening demand reduction has different climate impact than midday.
Related Tools
Related Terms
Grid Emissions Factor
The amount of CO2 emitted per kWh of electricity generated by the local grid, varying by region and time of day based on the generation mix. Ranges from 0.1 lb/kWh (hydro-heavy) to 1.8 lb/kWh (coal-heavy).
Peaker Plant
A power plant that operates only during periods of peak electricity demand — typically natural gas simple-cycle turbines that can start up in 5-15 minutes. They run a few hundred hours per year and charge premium electricity rates.
Merit Order
The sequence in which power plants are dispatched to meet electricity demand, ranked from cheapest to most expensive operating cost. Renewables and nuclear (near-zero fuel cost) dispatch first; expensive peaker plants dispatch last.