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Careful drivers

Christina Fell, Arup’s programme manager for the UK’s largest trial of ultra-low carbon vehicles, discusses the project’s findings so far

CABLED (short for Coventry and Birmingham Low Emission Demonstrators) is the largest of eight consortia from across the UK to participate in the Technology Strategy Board’s £25million Ultra Low Carbon Vehicle Demonstrator Programme and was the first to begin vehicle trials last year.

The consortium combines expertise from 13 organisations; the group is working together to develop, demonstrate and trial 110 roadworthy vehicles across the two cities over 12 months. The consortium partners include Arup (project leaders), Aston University, Birmingham City Council, University of Birmingham, Coventry City Council, Coventry University, E.ON, Jaguar Land Rover, LTI, Microcab, Mitsubishi, Smart and Tata.

The aim of the project is to find out how low emission vehicles are used by recording real-world data.

The resulting trial data being gathered provides some of the first behavioural information on long-term electric car ownership, usage and habits. The analysis provides real-life duty cycle information that will inform the development of charging infrastructure and smart grid networks, in-line with driver needs.

The first group of cars, 25 Mitsubishi i-MiEVs, were given to drivers in mid-December 2009. The drivers run their electric vehicles over 12 months to ensure they experience driving an electric vehicle through the whole range of seasonal conditions.

Each car has a GPS data logger to record journey details, which were updated during the trial period, meaning the charge history from the vehicles has been recorded for the last month. Further readings have also been recorded from meters installed as part of the domestic charging infrastructure at each user’s home.

One of the most significant findings from the first quarter results of the CABLED trial is how quickly drivers adapt to electric vehicles and how similar the use of electric cars is to their conventionally-powered counterparts.
Journey data indicates that modern electric vehicles are more than capable of catering for a typical driver’s day-to-day needs. Most journeys made by participants in the CABLED trial are in fact less than five miles (during this time conventional, fossil-fuelled engines are at their most polluting and catalytic converters are at their least effective). This is slightly less than the national average of seven miles per journey. CABLED drivers are completing an average daily mileage of 25 miles, which is well within the MiEV’s 80 mile range.
The CABLED team at Arup calculated that if all UK car journeys of less than 50 miles were made by electric rather than conventional vehicles, the savings in CO2 on a wheel-to-wheel basis would equate to taking 7.5million cars off the roads. While it may take many years to achieve this, CO2 and energy savings will also increase as the UK grid integrates more renewable energies.
Comparing initial data from the second quarter to the first quarter report, the cars have driven more miles, made more frequent journeys and completed more long journeys of 50 miles or more.

This increase in length of journeys suggests that people have more confidence in their cars, which is likely to be the result of growing familiarity with the vehicle’s range and their increased range in warmer temperatures (down to improved battery performance and less need on battery-draining heaters). Another contributing factor to the increase would be better road conditions – during January and February people were warned only to make necessary journeys due to icy roads. To get a clear indication of driver behaviour and seasonal usage trends, this data will be separated in the final CABLED report.
Early evidence shows that drivers habitually charge their vehicles, whether the battery is half full or nearly empty, in much the same way as laptop and mobile phone users. Unsurprisingly, the most popular time to charge vehicles was overnight, when inactivity ensures drivers can easily return vehicles to full charge by the morning and have a more than adequate range to meet their daily needs.

Previous studies of people driving electric vehicles for a few weeks have shown that most users proved unwilling to let the battery drop below half way. However, CABLED data, recorded over a period of months rather than weeks, reveals that the level at which drivers are willing to let the charge drop is much lower. 43 percent of charges took place when the battery was below half full. The distribution of pre-charging levels is fairly linear until one eighth of the charge is remaining, when just five percent of charges take place. Monitoring this trend over the rest of the trial period will give important information on levels of range anxiety.

The start of charging shows peaks at approximately 50 percent and 80 percent of the battery charge, possibly corresponding to users’ commutes between home and work. Vehicle charging data shows that the average charging time of the vehicles is two hours and the average increase in the state of charge is 30 percent. This means that an average charge would be from 70 percent to full or a top up of 50-80 percent.

Vehicle data indicates there is a peak in charging at 9am, which is not replicated in domestic data, suggesting that charging is regularly done at the work place.

All vehicle drivers in the trials have timers which allow them to delay the start of vehicle charging, to take advantage of cheap overnight electricity. The domestic data shows a second peak in charging late in the evening. This indicates some drivers are using timers to charge their vehicles overnight. However, only 20 percent have chosen the electricity tariffs with cheaper overnight electricity rates which should encourage them to do this.

The average domestic charge is 7kWh of electricity, with users charging at home four times weekly. This is an average daily usage of 4.5kWh, approximately equivalent to doing one load of washing a day in a washer-drier with an estimated cost of less than one pound per day.

Once all of the vehicle tracking and charging information is collated and analysed it will be used to inform the development of the next generation of electric vehicles and their batteries, and will prove invaluable when assessing implications for the national grid.

The second stage of the CABLED trial was launched in July, with 40 Smart cars. A further four manufacturers will be launching low carbon vehicles onto the roads of the West Midlands in coming months, consisting of 25 Tata Indica electric cars, 10 hydrogen fuelled Microcabs, five Range_e hybrid Land Rovers and five LTI electric taxis.

Although is still early days, it is clear that the findings of the CABLED trial, along with the knowledge of the consortium members will prove invaluable to energy providers, vehicle and battery manufacturers and town planners.Once combined with the results of the Technology Strategy Board’s other regional trials, it will ensure the UK is equipped with enough real-world information to facilitate the wider introduction of low carbon vehicles.