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Electric & Hybrid Cars: New Load, or New Resource?

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

Fortnightly Magazine - December 2006

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 for 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 both new load and new, distributed resources.

Electrons for Gasoline

Ultimately, the economics of displacing gasoline with electricity 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 off-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 PHEV-load 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.

The NREL study assumed that 40 percent of the PHEV daily miles traveled were obtained using electricity. This is equivalent to a PHEV with an all-electric range of between 20 to 40 miles—so called PHEV20 and PHEV40 respectively. While uncertainty exists about the PHEV architecture that is most marketable, the National Economic Council’s Advanced Energy Initiative established PHEV40 as its goal. 5 Depending on the average vehicle miles traveled in each region, between 4 kWh and 6 kWh on average per day are needed to meet 40 percent of drive miles with electricity. Fig. 2 presents estimates of the increased energy consumption for each region by PHEV penetration rate. This type of new load represents an opportunity for the electric utility industry to expand sales without contributing to system peak.

Further benefit to the electric-power sector from the introduction of PHEVs include increased load factor, for both generation and transmission facilities,