Aggregate data to fuel types using subplant-level rather than plant-level data

[grgmiller]

If a plant has multiple generators that burn multiple fuels, all of the generation and emissions for this plant are assigned the plant primary fuel type when aggregating to the fleet level or other higher level aggregations.

For example, in 2022, the Meramec plant overall burned more natural gas than coal, although only units 1 and 2 burned natural gas, while units 3 and 4 burned coal. However, since this plant was categorized as natural gas, all of the coal emissions also got lumped in with natural gas, which can throw off the fleet totals.

Going forward, we should probably try and publish subplant-level data (at least annually) as well as perform all fleet-level aggregations based on subplant-level data, rather than aggregating the already aggregated plant-level data.