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Task 15, Plug-in Hybrid Electric Vehicles (PHEVs), experts suggest different PHEV type success odds for EU vs. U.S.

January 24, 2013 11:20 AM

 

Members of Task 15 have been working on improvement and standardization of methods of analysis and prepared updates of vehicle comparisons in the area of PHEVs. It was agreed that evaluation of potential initial financially viable niche markets for PHEVs requires detailed breakouts and characterization of driving patterns.

Members agreed that potential disaggregation of customer groups, such as city, urban (or suburban, for the U.S.) and rural driving is important. 

DLR (German Aerospace Center) separated the MiD 2008 data for Germany into the three categories (rural, urban, and city), clearly illustrating that for trips up to about 35 km, average speeds decrease as one moves from rural to urban to city driving.

More importantly, consistent with prior U.S. findings, this also indicates that as average trip length increases, the average speed also rises regardless of the point of origin of the trip. It was decided that an approximate method to translate driving cycle simulations into predictions of fuel savings must upwardly adjust predicted average speeds as predicted annual driving increases.

graph_1_task_5_jan_2013_nwsltr

Average driving speed in Germany as a function of average trip distance and place of residence (DLR analysis based on MiD 2008 data)

The prior EVS 26 paper by Propfe et al. had not adjusted driving cycles (and simulated average speed) as a function of predicted annual driving distance. It was agreed that this would be corrected in future papers. The method used was to characterize an expected daily average speed associated with an annual driving prediction, select representative available driving cycle simulations above and below that speed, and construct a weighted average of fuel consumption savings for which the weight for the two selected cycles was consistent with the annual average speed predicted. For any speed selected, the European driving cycles and U.S. driving cycles were drawn from those applicable on their continent. 

A question of interest was whether significant differences in predicted market viability could result if one were to evaluate plug-in vehicles on the basis of (1) official tests for rating of the fuel economy of vehicles vs. (2) actual driving behavior. A joint paper was written in which U.S. and European analysts compared their estimates of the market viability of selected PHEVs.

It was agreed that total cost of ownership (TCO) estimates should be based on “real world” driving rather than official certification cycle driving. Outside of the agreed method of estimating appropriate speed and selection of driving cycle for the TCO evaluations, there remain many differences between the base case approaches used by European vs. U.S. analysts. 

The paper Comparison of Energy Consumption and costs of Different HEVs and PHEVs in European and American Context by A. Rousseau et al. was prepared and presented at the European Electric Vehicle Congress held in Brussels on November 19–22, 2012. 

Only three of the project’s seventeen simulated electric drive powertrains previously presented in the Da Costa et al. EVS26 paper Fuel Consumption Potential of Different Plug-in Hybrid Vehicle Architectures in the European and American Contexts were included. They were compared to a conventional vehicle (CV) with an automatic transmission powertrain. A parallel HEV, an input-split PHEV30km, and a series PHEV70km were evaluated for three distance groups—short, typical and longer. 

 

pic_2_Task_15_jan_2013_newsltr

                     Hybrid powertrain architectures considered.

 

Comparisons were made using current gasoline and electricity prices. Subsidies were not considered. The simulations are for mass-produced vehicles in about 2020:

  • For Germany, the HEV was always estimated to be the least TCO option.
  • For the U.S. the CV was the best at short distances; the HEV and PHEV30 were slightly better than the CV and almost identical to one another at typical distances; the PHEV30 was best at longer annual distances.
  • For the series PHEV70, which has much more pack kWh and more kW than the PHEV30, the added electric drive costs far outweigh the fuel cost saving benefits, particularly for U.S. estimates. However, even though it was consistently the least attractive of the three electric drive powertrains, in Germany it was estimated to be a better choice than the CV if driven longer distances. The penalty of the PHEV70 in comparison to the HEV and PHEV30 steadily narrowed as distance increased.

Based on this result, future investigation of alternative series PHEV designs appears reasonable to include in any follow-up study. 


Percent benefit in TCO according to drivetrain and distance considered

The investigation of official fuel consumption certification test cycles implied that the U.S. TCO success of the PHEV30 might not exist if the TCO analysis had been based on official U.S. test cycle and adjustment factors for PHEVs. As shown in the prior Task 15 EVS 26 paper by DaCosta et al, the official U.S. Highway certification driving cycle appears to be an anomaly, predicting far less charge-sustaining (HEV mode) fuel consumption benefit for the PHEV30 (and other PHEVs) than for any other driving cycle simulated. For the EU case (Germany), the estimated superiority of the HEV might be retained. The EU NEDC certification test was found to be particularly favorable to the HEV.

For more information, email  Mr. Dan Santini.

 

Contributed by Mr. Dan Santini
Task 15 Operating Agent

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