UTILITY SYSTEM IMPACTS

Editor’s Note: These series are selected from manual Electric Vehicle Community Market Launch Manual: A Guide to Prepare Your Community for Electric Vehicles which was prepared by the Electric Transportation Coalition (ETC) and the Electric Vehicle Association of the Americas (EVAA) in cooperation with the U.S. Department of Energy (DOE) and the U.S. Department of Transportation (DOT).

The EV demand is much larger than that of most electrical appliances. In fact, EVs are likely to constitute a residence’s largest single load. Further, because EVs are mobile, they can be charged at various locations. Because of these characteristics, future charging of a significant number of EVs could present a challenge to utility planners. (See Volume III for technical information on the impact of EV charging on the utility system.) To meet the community’s needs, the local electric utility must be able to fuel all EVs upon request using the most reliable and economic means. Community planners should therefore work with utility planners as early as possible to ensure that sufficient electricity will be available.

This section briefly describes:

  • How electric utilities might study the impact of EV charging on their systems
  • How EV loads can be controlled
  • Minimizing the need for electric panel capacity upgrades

Utility Issues

An electric utility that wants to become EV Ready might consider the following steps:

  • Identify the size and likely locations of the EV electrical load
  • Identify utility system limits and any system upgrades required as a result of the addition of EVs
  • Study the load profile implications of EVs and evaluate load management opportunities
  • Determine the best approaches to manage future EV loads

Load Management Options

Strategies for safe, reliable, and economical management of EV loads hinge on employing load management techniques that equitably share the cost and split the savings between the EV customer and the electric utility. Load management provides a means for influencing customer use of electricity to lower the cost of service by decreasing the peak demand on generation and distribution systems. One way utilities manage loads is to offer customers more attractive energy rates during off-peak periods and to charge higher rates during the peak. Utilities can also, with customer agreement, manage loads by controlling when electricity can be provided to the customer.

For EVs charged at residences, a real-time pricing mechanism (see Volume III for a list of time-of-use rates) coupled with a ‘‘smart charger’’ programmed for least-cost charging is one possible load management option. At an EV fleet facility, real-time pricing to encourage off peak charging, coupled with devices that stagger the charging of many EVs at one site, is another load management technique. And at public charging facilities, the operator might consider using some type of energy storage device. However, the price of electricity purchased at these facilities will likely be at a premium to reflect thehigher cost of such facilities.

This case study looks at SCE’s experience with EV load management:

Southern California Edison Company SCE has proposed a load management strategy that relies on a load management device and time-of-use rates to provide the user with a safe, reliable, and cost-effective method of charging an EV. Load management devices may include timers, voltage and current limiters, load-cycling devices, direct load-control devices and smart revenue meters. Some of these devices may ultimately be used in residential structures as part of the Electric Vehicle Interface (EVI) system that is being developed by SCE. The EVI will establish two-way communication between the EV owner and SCE for cost-effective management of EV loads.

Electric Panel Capacity Upgrades

Residential electric panel capacity can be an issue for consumers installing EV charging facilities. Ideally, EV buyers would be aware of this issue before making the purchase, as panel upgrades or other solutions can add to the cost and time of making a home EV-Ready.

In brief, each electrical panel can deliver only a certain amount of amperage at any given time. If the addition of 40 amps of EV demand exceeds that capacity, EV purchasers need to consult with local building officials and utility representatives to identify solutions and cost. One choice might be to replace the panel with a panel large enough to handle the additional load. Another might be to invest in a smart charger that allows EV charging only when other high-amperage appliances are not operating. Still another option might be a load management device that restricts EV charging to low demand off-peak hours, or turns off some other electric load before allowing the EV charging circuit to engage.

Communities can mitigate this problem for new houses by encouraging developers and builders to consider EV charging load requirements when choosing the size of electrical panel to install during new construction. Further, IWC is undertaking a survey and study to determine whether EV charging needs to be considered a ‘‘continuous load.’’ Depending on findings, the group is planning to decrease the continuous load requirement of electric panels by modifying the 1999 National Electric Code. The utilities that have been studying this issue have found the problem may not be widespread, as discussed in the case studies below:

California Utilities
In 1993, SCE, Pacific Gas and Electric Company (PG&E), and LADWP studied the cost to retrofit about 300 single-family/ multi-family residential structures with a240 volt/40ampere electric circuit from the existing electric service panel to the garage location. (The cost of off board chargers and/or control panels were not included in the study.) Results showed that roughly two-thirds of those surveyed required no electrical panel upgrades.

Consolidated Edison of New York (Con Edison)
Seeking to minimize infrastructure costs during the PrEView program, Con Edison surveyed candidate participants from a list supplied by GM to identify those who had 3-wire, 220 volt, 100 amp service entering their off-street parking locations. This criterion did not eliminate any potential participants. In the few cases where the panel capacity would not support additional breakers, Con Edison installed a subpanel. One user agreed to forego using the home’s air conditioner while the vehicle was charging, flipping as witch to control the selection. Infrastructure costs averaged $750 for each installation.

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March 15, 2008 · Filed Under Electric Car Conversion Blog

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