State of Charge: Technical Appendix

The document provides the technical basis for estimating EV charging emissions and costs in the US. It explains the use of average emissions intensity based on EPA eGRID data, adjusted for transmission losses and upstream feedstock emissions. It also describes a modified Oak Ridge Competitive Electricity Dispatch (ORCED) model used for hourly emissions estimates. Additionally, it outlines the process for calculating residential charging costs across 50 US cities, accounting for tiered rates, time-of-use (TOU) plans, and specific utility data.

• The analysis uses average emissions intensity rather than marginal emissions to provide consumers with an estimate of typical global warming emissions on the current grid, treating electricity as a "shared resource, or pool of electrons, available to all electricity consumers."
• Regional emissions estimates are based on the EPA's eGRID 2012 v1.0 database (using 2009 data) for 26 subregions, which are adjusted to include transmission and distribution losses and upstream emissions from mining and transporting fuel.
• Upstream feedstock emissions rates were calculated using the GREET life-cycle emissions model developed by Argonne National Laboratory, with natural gas rates used as a conservative estimate for "generic fossil" fuel types.
• To estimate hourly emissions intensity for 13 regions, the authors used a modified Oak Ridge Competitive Electricity Dispatch (ORCED) model, which estimates the mix of power plants generating electricity based on hourly demand levels.
• Hourly emissions results indicate that most regions have slightly higher average emissions intensities during non-peak hours, though this varies; for example, in California, evening intensities can be higher because hydro dams are controlled to generate more power during daytime peak demand.
• Residential charging cost calculations for 50 US cities assume a daily driving distance of 30 miles and a plug-to-wheel efficiency of 0.34 kWh/mile, based on the first-generation Nissan LEAF.
• For time-of-use (TOU) rate plans, the analysis assumes that 70% of charging is performed during off-peak hours and the remaining 30% occurs at random times throughout the day.
• In cities with tiered electricity rates where the EV and house share a single meter, the analysis treats EV charging as the "last" electricity used, meaning it incurs the highest-tiered rates.

APA

Union of Concerned Scientists (n.d.). State of Charge: Technical Appendix. https://www.ucs.org/sites/default/files/2019-09/electric-car-global-warming-emissions-appendix.pdf

Chicago

Union of Concerned Scientists. State of Charge: Technical Appendix. n.d. https://www.ucs.org/sites/default/files/2019-09/electric-car-global-warming-emissions-appendix.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=State of Charge: Technical Appendix |url=https://www.ucs.org/sites/default/files/2019-09/electric-car-global-warming-emissions-appendix.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientistsndstate, author = {{Union of Concerned Scientists}}, title = {{State of Charge: Technical Appendix}}, institution = {Union of Concerned Scientists}, url = {https://www.ucs.org/sites/default/files/2019-09/electric-car-global-warming-emissions-appendix.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }