Electric Vehicle Charging Infrastructure
The National Electric Code Article 625 outlines the code requirements for electric vehicle charging infrastructure. Currently, there are three levels of charging level standards being developed for the U.S. through the Society of Automotive Engineers (SAE).
Level 1 is a 110-volt power supply on a 15-amp or 20-amp dedicated circuit. Level 2 is a 240-volt power supply. Levels 1 and 2 are standardized under the SAE J1772 best practice, which mandates only one plug for all makes and models produced for the U.S.
Level 3 and DC fast charging are not yet standardized but will use higher power than what will be seen in residential charging.
Each level is outlined below in relation to different kinds of electric vehicles.
Plug-in hybrid models are being designed for Level 1, which is the standard 110-volt electrical supply, in order to utilize home charging. Plug-in hybrid battery systems will be able to manage higher charging levels, but the initial marketing suggests the 110-volt as the automotive manufacturer default.
The Society of Automotive Engineers is proposing a standard to mandate that all grid-enabled vehicles, not just plug-in hybrid models, have Level 1 charging capability.
While this may not provide much support for larger battery electric vehicle battery packs, it does provide greater access to emergency charging from 110-volt if needed. A 110-volt supply may take more than eight hours to fully charge a plug-in hybrid, and is not an immediate threat to power systems.
It is important, however, that consumers realize the role they will play in the power system as we transition from petroleum to electricity as the transportation fuel. Consumers, utilities and everyone with a stake in the smooth operation of the power grid needs to be involved in creating the habits of charging behavior that will support that goal.
Despite the Society of Automotive Engineers' backing of Level 1, major automotive manufacturers have lined up behind Level 2 charging as the primary standard for the commercial vehicle releases in 2010. Level 2, a 240-volt supply, requires that dedicated electric vehicle supply equipment be hardwired to the location where a vehicle will charge, such as a home or public garage.
Level 2 offers a smaller window of charge time, usually half the requirement of Level 1, but may require electrical infrastructure upgrades for home charging. These upgrades in the home require new processes to manage during the purchase of the car and will likely affect the local electric power distribution system as well, depending on how fast the transition to electricity as a fuel occurs and how large the increased load on the particular distribution circuit.
Level 2 will likely be the charge level of choice for public outlets, such as on a city street or in parking garages. Commercial businesses may choose to offer vehicle charging options as a service to their customers or support a corporate sustainability strategy.
Level 2 has a range of power demand from 2.5 kilowatts to 19 kilowatts. Initial vehicles produced for mass market will likely have only a 3.3 kilowatt onboard charger, eliminating the immediate need for high-power home charger supply upgrades.
DC Fast Charging
DC fast charging replicates the speed of refueling in a typical gas station. DC fast charging is not the U.S. standard but is being deployed in the TVA service area as part of the TVA's EV (Electric Vehicle) Project. TVA is engaged in DC fast charge research to understand the localized impacts of this type of system on the power grid.
The three levels of charging under development have different hardware requirements. For Levels 1 and 2, an open standard plug and coupler for all vehicle makes and models is finalized under the SAE J1772 naming convention. The SAE J1772 has three power pins and two communications pins for advanced metering infrastructure applications.
Standard hardware for Level 3 and DC fast charging is still under development and will require a larger plug and coupler as well as designated distribution hardware. Level 3 and DC Fast Chargers may also require attendants to operate the hardware for commercial use. It is conceivable that cars, especially battery electric vehicles, will have both couplers for charging in the U.S. in the short term.
It is important to note that costs associated with charging infrastructure are in direct correlation to hardware standards. Utilities are focusing on charging infrastructure; therefore, it is critical to participate in the development of these standards by groups such as the Society of Automotive Engineers.
TVA is engaged in an Infrastructure Working Council facilitated by the Electric Power Research Institute and made up of Society of Automotive Engineers representatives, automotive manufacturers, electric power utilities, charging infrastructure manufacturers and other stakeholders.
Utilities are constantly planning and implementing upgrades to their individual systems. Knowing what potential opportunities and challenges the electric vehicle market offers is critically important. Estimating who will purchase these vehicles as they become commercially available, in order to plan system upgrades, is, at the present, extremely difficult.
Learning about current circuit hardware is an effective way to get ready for future upgrades. Unfortunately, many power distributors are at a disadvantage because without detailed paper records, they do not know which assets are where and how long they have been in place.
As new technologies allowing easier access to this type of information become available, power distributors will be able to better predict where costly upgrades are required in the local systems that are affected the most.
Reducing the impact on the grid can be accomplished in many ways, including increasing consumer knowledge of the utility’s operational issues, developing an effective AMI strategy and developing charging location networks.
Consumers can learn through economic signals such as time-of-use rates as well as through marketing campaigns targeting their core beliefs. AMI technologies enable load leveling to the point of shutting off the vehicle charger during peak emergency times. Charging networks provide opportunities for utilities to make upgrades to support public charging.
Level 3 charging can also be incorporated in charging-network strategies and located in commuting traffic patterns but near a substation or recent distribution circuit upgrade. Careful planning of the charging networks will help utilities encourage market development electric transportation and lower the risk of unpredicted consequences.