Transmission network-based energy and environmental assessment of plug-in hybrid electric vehicles
Introduction
Plug-in hybrid electric vehicles (PHEVs) utilize advanced batteries to obtain between 20 and 60 miles of fully-electric driving and afterwards uses a traditional hybrid electric power train for range extension [1], [2]. In the future, PHEVs will likely shift the transportation network's dependence away from petroleum and towards the electric grids, thus inducing a significant transformation within the electric power and transportation sectors [3], [4], [5]. Moreover, the pollutant emission changes from mobile sources of vehicles to point sources of power plants as a result of PHEVs will affect air quality, especially at urban centers.
Recently studies have begun to investigate fuel mixtures, emission changes and grid reliability issues associated with PHEV usage [3], [4], [5], [6], [7], [8], [9]. The findings from those studies have advanced our understanding on the energy and environmental impacts of PHEVs. Overall, the penetration of PHEVs into the automobile market is expected to reduce tailpipe emissions as well as the total emissions accounting for the increased emissions from coal, natural gas and oil power plants [5], [6]. A unit commitment model without transmission constraints was incorporated into an economic dispatch model of the Electricity Reliability Council of Texas (ERCOT) region to evaluate the change in generator dispatches resulting from PHEV deployment [7]. Researchers also analyzed the potential impacts of PHEVs on electricity demand, supply, generation mixture and emissions in 2020 and 2030 in 13 regions specified by the North American Electric Reliability Corporation (NERC) and the U.S. Department of Energy's Energy Information Administration. Modeled without transmission constraints of the electric power network, the study further assumed a uniform fuel mixture for electricity generation within the region [8]. Using a 10-bus reduced model for the Ontario transmission system, a study in 2010 analyzed the optimality of PHEV's off-peak charging on the reliability of the region's power system [9].
This paper shows the need to incorporate realistic engineering and operational constraints of the power transmission network into an economic dispatch model when assessing the regional impact of PHEVs on the varying fuel mixture and emissions of power generation. We show that these network constraints noticeably alter the dispatch of generation from that based purely on economics of individual generators. Consequently, an economic dispatch model with network constraints can more realistically model the regional impact of PHEVs.
In this paper, we present our study on the energy and environmental impacts of PHEV-40 (PHEV with a 40-mile all electric range) with various market penetrations (replacing the corresponding conventional vehicles with PHEVs) in the New York Metropolitan Area (NYMA) using an economic dispatch model subject to realistic engineering and operational constraints of the reduced NPCC AC power network [10]. Moreover, every generator in our model has an associated fuel type (coal, nuclear, hydro, natural gas and oil), cost function for power generation and emissions characteristics (CO2, NOx and SOx), which we obtained from corresponding Independent System Operators (ISOs). Based on driving patterns of commuters working in New York City (NYC), we aim to evaluate the effects of different PHEV penetrations and charging scenarios on generation fuel mixture and emissions in the Northeast Power Coordinating Council (NPCC) region for the summer and winter seasons.
Section snippets
Transportation system modeling
This study of the transportation system in NYMA focuses on vehicles commuting in-and-out of NYC. The U.S. Department of Transportation's 2000 Census Transportation Planning Package (CTPP), which contains data specifically designed for transportation planners, reveals that approximately 1,040,000 people within NYMA commute daily to NYC by personal vehicles [11]. These vehicles usually congest the city's main roads and highways, thereby contributing to the high pollution levels near the freeways
Load profiles
Fig. 1 represents the electric demand profiles for the NYMA during a 24-h period in two different seasons and under various penetration scenarios. The unregulated charging of PHEVs aggravates the late afternoon and early evening peak electric demand because the additional load coincides with residents turning on their home appliances. In contrast, with regulated charging the additional demand will help to fill the valley of the demand curve in the late night and early morning, particularly in
Effects of network constraints
As described at the beginning of this paper, many existing PHEV assessments do not contain network transmission constraints. However, the power to charge PHEVs must be delivered by the grid, and therefore such power flows must adhere to transmission constraints. Using our reduced model of the NPCC grid, we show that engineering and operational constraints in a realistic US power grid, such as line impedance, line flow and bus voltage limits, significantly alter the generation dispatch from a
Conclusions
This paper demonstrates that network-constrained economic generation-dispatch models add significant realism in assessing the impact of PHEVs on regional power systems and the associated pollutant emissions. Using a model of the AC transmission network of the Northeast Power Coordinating Council region and a data-based transportation model of commuters in the New York Metropolitan Area, this paper shows that (1) coal, natural gas and oil units are on the margin in the winter, and natural gas
Acknowledgements
We thank Timothy Mount, Robert Thomas, William Schulze, Ray Zimmerman, Douglas Mitarotonda and Daniel Shawhan for their insights and assistance. We also thank the Cornell Center for a Sustainable Future (CCSF) and Consortium for Electric Reliability Technology Solutions (CERTS) for the funding support.
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