Electric Cars: Utility Windfall or Headache?

White paper by Steven Letendre, Paul Denholm, Paul and Peter Lilienthal looks at impact of electric drive vehicles on the national power grid.

Published: 16-Jan-2007

The industry must join a growing chorus in calling for new technology.

The prospect of millions of vehicles plugging into the nation's electric grid in the coming decades never has been better. In 2005, hybrid electric vehicles (HEV) reached 1.2 percent of new cars sold in the United States, more than doubling the number sold in the prior year. Vehicle manufacturers, betting on this trend accelerating in the coming years, are rushing to bring HEVs to their dealers' showrooms.

The evolution ot HEVs to allow charging from the electric grid-so called plug-in hybrids (PHEV)-is assumed by many to be desirable, even inevitable. Indeed, a growing movement to bring PHEVs to market has emerged, bolstered by the undeniable economic and national-security benefits that result from displacing gasoline with electricity.

One highly visible grassroots campaign called Plug-In Partners seeks to demonstrate to the major automobile manutacturers that a national market exists for flexible-fuel PHEVs; dozens of businesses, utilities, municipal governments, and environmental groups have joined the Plug-In Partners campaign.

While there are no commercially available PHEVs on the market, a number of prototypes have been built and tested. The most established PHEV program is housed at the University of California Davis, where Professor Andrew Frank works with students designing and building prototype PHEVs. A second development project involves collaboration between the Electric Power Research Institute (EPRI) and DaimlerChrysler. They produced, and are in the process of testing, several prototype plug-in hybrid vans using the Sprinter platform. (Editor's Note: Tesla Motors recently introduced an all- electric vehicle. see sidebar, p. 34.)

Two startup firms plan ro offer conversion kits for current generation hybrid electric vehicles to allow grid charging of the on-board battery pack. These conversions kits offer the potential to almost double an HEVs fuel efficiency rating to 100+ miles per gallon by increasing the size of the battery storage system and installing the hardware and controls to allow charging from the electric grid.

There is some indication that at least one major auto manufacturer is developing next generation PHEV technology. This summer, Jim Press, president of Toyota's North American subsidiary, announced that the company was looking at developing a plug-in hybrid that travels greater distance without gasoline than their current hybrid models. Toyota is the leading manufacturer of HEVs, selling over 50 percent of all hybrids purchased in the US in 2005.

The authors believe that the commercial success of PHEVs will hinge on an aggressive development and marketing effort by a major auto maker. Support from the electric-power industry could provide further impetus for a major automobile manufacturer, such as Toyota, to pursue PHEV technology.

The potential that PHEVs offer to lower fuel costs, reduce petroleum consumption, and decrease harmful emissions is described elsewhere.' The likely impact on the electric grid from an increasing number of vehicles plugging in is not yet fully understood. This is due in part to key variables that are difficult to predict, such as likely PHEV design characteristics (e.g., battery size and efficiency) and market penetration rates.

This article sheds light on these important issues using reasonable assumptions tor each of these key variables.

We begin with an assessment of the increased load that PHEVs would represent under a range of assumptions. Next, we evaluate PHEVs serving as distributed-power resources, targeting high-value markets for fast response, short duration grid-support services; this concept has become known as vehicle to grid.2 Finally, we summarize the opportunity and challenge that PHEVs represent to the electric power industry.

We believe the system-wide impacts of an emerging fleet of PHEVs are fully understood only when these vehicles are considered as boch new load and new, distributed resources.

Electrons for Gasoline

Ultimately, the economics of displacing gasoline with clectricity should drive consumer demand for PHEVs. The cost of electricity to drive a vehicle the same distance as one gallon of gasoline is equal to approximately $1-or even less if oil-peak electricity prices are assumed.3 Furthermore, as discussed later in this article, PHEVs potentially could generate revenue for the vehicle owner by providing grid-support services. Combined, these value propositions could serve to usher in an era of advanced vehicles with dramatic reductions in gasoline use and tailpipe emissions.

Can the current and planned electric-power infrastructure meet the increased demand from PHEVs?

Fig. 1 presents load-duration curves under a range of assumption about PHEVs, from a base case with no PHEVs to an aggressive case assuming 50 percent penetration. The graph illustrates that PHEV charging does not necessarily contribute to the system peak, provided an optimized PHEV charging regime is adopted. The graph was generated using a PHEVload tool, which simulates PHEV charging on an optimized 24-hour cycle for a utility control area in the Midwest. This simulation was performed for six different regions for which hourly electric load data was available. The results presented in Fig. 1 were consistent across the six regions.

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