Depending on the location of new generation resources, their power will have more or less impact on the carbon intensity of overall generation. For instance, a wind power plant that replaces power from a coal plant should have a more significant impact on overall emissions than the same turbines if they replace power from a combined-cycle natural gas plant. Adding another solar panel to a region that is already saturated with midday carbon-free power that has to be curtailed, will displace much less carbon emissions than the first panels, if they replaced fossil resources at all hours they generated power.
Energy system modelers have quantified the “marginal emissions displacement” or “locational marginal emissions” of new renewable resources in various geographies so that energy buyers and developers can understand where new resources make the most impact on total carbon emissions.
The papers and slides on this topic outline the methods used to quantify marginal emissions, and detail how they vary across regions.