Suggested Citation:
McCarthy, Ryan W. (2009) Assessing Vehicle Electricity Demand Impacts on California Electricity Supply. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-09-44

Achieving policy targets for reducing greenhouse gas (GHG) emissions from transportation will likely require significant adoption of battery-electric, plug-in hybrid, or hydrogen fuel cell vehicles. These vehicles use electricity either directly as fuel, or indirectly for hydrogen production or storage. As they gain share, currently disparate electricity and transportation fuels supply systems will begin to “converge.”  

Several studies consider impacts of electric vehicle recharging on electricity supply or comparative GHG emissions among alternative vehicle platforms. But few consider interactions between growing populations of electric-drive vehicles and the evolution of electricity supply, especially within particular regional and policy contexts. This dissertation addresses this gap. It develops two modeling tools (EDGE-CA and LEDGE-CA) to illuminate tradeoffs and potential interactions between light-duty vehicles and electricity supply in California. 

Near-term findings suggest natural gas-fired power plants will supply “marginal” electricity for vehicle recharging and hydrogen production. Based on likely vehicle recharging profiles, GHG emissions rates from these plants are more than 40% higher than the average from all generation supplying electricity demand in California and 65% higher than the estimated marginal electricity emissions rate in California’s Low Carbon Fuel Standard. Emissions from power plants supplying vehicle recharging are usually highest from 5pm-8pm, when they are 20% higher than their typical low value, from 2am-4am. Plug-in hybrid vehicles are 25-42% more efficient than conventional, gasoline hybrids, but reduce GHG emissions by less than 5%, because marginal electricity is currently much more carbon-intensive than gasoline in California (based on likely recharging profiles). 

Over the long term, adding vehicle recharging or renewable generation to the grid can have important impacts on how electricity is supplied. Vehicle recharging shifts capacity and generation from poorly-utilized peaking power plants to more highly-utilized baseload plants with lower operating costs. Adding renewable generation has the opposite effect, which may be partially mitigated if vehicle recharging can be made to follow renewable generation. Achieving long-term targets for deep reductions in electricity sector GHG emissions requires significantly increasing renewable or nuclear generation and reducing per-capita electricity demand or avoiding new capacity from fossil power plants without carbon capture and sequestration.