BEV Incremental CO ₂ Emissions in a Ranked Order Electric Grid

Battery Electric Vehicles (BEV) have been sold as ‘Zero Emissions Vehicles’ (ZEV) by governments to reduce transportation CO₂. While they are not ZEV because they run on grid electricity, they could be ‘effectively ZEV’ if the incremental CO₂ is ‘very small’. At the national level, this is estimated using following metrics: (1) Internal Combustion Engine Vehicle (ICEV) fuel consumption, from the total US gasoline consumption divided by the total fleet miles driven, 25 mpg or 350 g CO₂/mi, (2) Strong Hybrid Electric Vehicles (HEV) about one third less, 240 g CO₂/mi. (3) BEV energy consumption, using data from systematic on-road testing of a wide range of vehicles, estimated at 40 kWh/100 mi for a US sales mix. (4) Electricity marginal CO₂: in a ranked order grid, zero-CO₂ sources are prioritized and supplemented by fossil sources. IEA hourly data show that the US 48 contiguous states are self-contained, with zero-CO₂ sources providing a third of total demand. The response to hourly demand changes comes largely from natural gas and coal power stations, with EPA data showing a combined marginal CO₂ of 600 g CO₂/kWh. On replacing an ICEV by a BEV, the reduction in gasoline use, - 350 g CO₂/mi, is offset to two thirds by higher electricity consumption, 40 x 600 / 100 = + 240 g CO₂/mi. BEV marginal CO₂ is therefore similar to HEV, and not ‘much smaller’ than ICEV. This is because HEV engines and fossil power stations have similar efficiency and similar fuel CO₂ intensity.