Electric Vehicle Charging in the 21st Century
Comis, David L.
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The emergence of electric vehicles brings new power and energy demands to the electric grid. This paper considers the question: If all passenger vehicles converted to electric power, would coordinated electric vehicle charging be required to prevent damage to distribution transformers or to mitigate the need to build new electric generators? Six potential vehicle charging strategies were considered: Unconstrained (no time constraints), Time of Use (TOU) Start (start when the electricity rate drops to the off-peak period), TOU End (driver specifies the time when the vehicle must be charged - the vehicle decides when it needs to start charging during the off-peak period), Flat (coordinated charging to flatten the load curve of the Regional Transmission Organization (RTO), Flat Algorithm (coordinated charging to minimize the ramp rate and to flatten the load), and Alternate TOU End (like TOU End but allows vehicle charging end times to follow the normal pattern of people going to work). Using the PJM calendar year 2014 load data and day-ahead pricing data, the yearly energy costs, ramp rates, and greenhouse gas emissions of each charging strategy were examined. Coordinated charging strategies (Flat, Flat Algorithm and Alternate TOU End) result in the lowest overall costs, but the highest greenhouse gas emissions. The Time of Use strategies (TOU Start and TOU End) result in the highest overall system cost and the highest ramp rates, but the lowest greenhouse gas emissions. Each of these strategies produces a 50-70% reduction of greenhouse gas emissions from those of the current internal combustion vehicles. Some form of charging coordination is required, at both the global and local level, to minimize the need to add or replace electrical infrastructure.