The macroscopic studies are undertaken to understand the consumer requirements when adopting PHEVs. Some of the parameters which are typically recorded to analyse consumer behaviour are charging duration, distance travelled between charge events and energy consumption per unit distance. However, the first prototype PHEV was built only in 1996 and mass-produced commercial PHEV such as the Chevrolet Volt, Toyota Prius PHEV, Ford C-Max Energi, BYD F3DM and Fisker Karma have become available only since 2010. Therefore, these consumer studies make use of only a few vehicles and clearly defined market segments. Therefore, the
results of the studies cannot be held as best representative for a typical driver. For completeness, current demonstration vehicles from other manufactures include Ford Escape Plug-in Hybrid, Volvo V70 Plug-in Hybrid, Suzuki Swift Plug-in, Audi A1 e-tron, Dodge Ram 1500 Plug-in Hybrid, and Volkswagen Golf Variant Twin Drive. It has been assumed the data from these vehicles have been analysed in-house and hence data is not available in the public domain.
However, there are several EV trials among which two are listed here. The next two programmes presented are from a retro-fitted PHEV trial and a website report of customers using PHEVs [45, 89].
The MINI E Consumer Study
There have been several EV user studies around the Mini-E programme [15, 86]. It is one of the largest studies to date. The programme consisted of two 6 month periods where during each period 40 EVs were given to different households for evaluation. The vehicle used was a Mini Cooper powered by a 150 kW EM and a 35 kWh battery pack. The expected range of the EV was 250 km over the NEDC. An important finding is that 94% of the users drove less than 160 km per trip. However, an interesting consideration is that these cars were used as second cars and 14% of the trips could not be completed on average because of range or cargo space limitations. It is argued that this issue has to be addressed due to the high cost implications of purchasing a zero CO2 emission powertrain. In such a scenario a PHEV with an optimised AER to address the majority of the trips would have been better suited.
Cenex Smart ED Trial Programme
This study forms one of the source data for this research. The details of the study are discussed further in Section 3.1. The objective of the study was to analyse the driving patterns of EVs [9]. Among the trips 93% of them were started with over 50% battery SOC. This attributes to the fact that the majority of the users charged the vehicle every day.
PHEV Demonstration and Consumer Education, Outreach, and Market Research Program
This study involved the evaluation of retro-fitted hybrid vehicles to include a plug-in capability [45]. A standard Toyota Prius with a 1.4 kWh battery was upgraded by the company Hymotion to a 5kWh battery pack with a plug-in capability. The vehicle had a 30 mile (48.2 km) theoretical EV range. The vehicles were given to
67 different households which were using them as their second car for four to six weeks each. An interesting outcome of the research is that the charging behaviour is related to infrastructure issues rather than user behaviour. A subset of the results due to their varied performance is shown in Figure 2.1. The area of the circles represent the mileage covered during the trial programme for each household. The x axis shows the percentage of miles driven in charge depletion (CD) mode. In this mode the use of the battery is maximised. The y axis shows the corresponding fuel consumption in miles per gallon (mpg). From the figure, although it is obvious that the percentage of miles driven in CD mode improves the fuel consumption, there does not seem to be a relationship between miles covered and fuel consumption. This fact reiterates the point that in a PHEV the charging profiles and the AER have a significant effect on fuel consumption compared to total distance covered.
Figure 2.1: Fuel economy recorded during a PHEV trial programme [45]
VoltStats.com
The website has reports from the live datalogs of the PHEV Chevrolet Volt sold in the US [89]. The on-board logger gives trip-wide statistics which are then displayed on the website. Trends can be determined such as electric range driven and the average fuel economy achieved. Figure 2.2 shows the fuel consumption of the Chevrolet Volt among 1400 drivers listed on the website to date. However, the duration for which the vehicle has been driven is not known. Since it is an active website with each new addition to the fleet of cars signed-on, the data changes. The fuel consumption is a definite function of the amount of electric miles driven, as seen by the green line which shows the percentage of miles driven electrically.
Although data and trends could be analysed at the trip level with large data-sets they do not contain sufficient resolution to predict energy consumption for specific
0 200 400 600 800 1000 1200 1400 0 1 2 3 4 5 6 7 8 9 10 Driver Number Fuel Consumption (l/100km) 0 200 400 600 800 1000 1200 14000 10 20 30 40 50 60 70 80 90 100
Percentage of distance driven as EV (%)
Figure 2.2: Fuel economy of Chevrolet Volt
scenarios based on road-type and traffic condition. Therefore, in the next stage of the review of real-world usage, examples are shown as to how the data maybe split into smaller sections for analysis.