18 Apr 2009

Electric Dreams

Recent activity in the electric car market has given rise to hopes that the eventual dream of a fossil-fuel-free transport system might one day be realised.

    There are still, however, two major hurdles to overcome:
  1. Range - 50 miles per charge is poor, and as batteries age this will only shrink
  2. Refuelling - Even if refuelling stations can fully charge a battery safely in about 10 minutes, the technology required for fast-charging is more complex than slow charging, and is, in any event, dependant on the battery technology in use. Also, for most people it is not practical to charge their vehicles at home or work, leaving cables lying around.

Here is a concept that will not only resolve these two issues, but make the transition to electric cars entirely viable.

User-portable Battery Packs

The car industry needs to adopt a standard for electric cars so that they all contain sets of identically sized battery packs, light enough, or well enough designed, to be removable from the vehicle and taken indoors for charging.

Imagine, as an initial design concept, a car with say 50KWh of battery capacity, which is enough for around 200 miles. 10KWh of this in in a single reserve pack, slung under the car roughly where current designs put the fuel tank, protected by a steel plate or similar from road debris, and replaceable quickly and easily at a garage. The remaining 40KWh is in 8 5KWh battery packs mounted under the bonnet in an array capable of controlled installation and release.

A new li-ion car battery can achieve around 125Wh/Kg, so a 5KWh battery would weigh in at around 40Kg, giving a total battery weight in the car of 400Kg. For comparison, a 4-cylinder engine, plus gearbox, plus 50litre fuel tank can easily exceed 400Kg, and in the US the total weight of an average vehicle is in excess of 2000KG.

Now, it isn't practical to ask all car drivers to lift a 40Kg weight out of a car and onto some trolley or platform, although most fairly fit men could manage it. Instead, there needs to be a system where the battery can be slid out of the space on rollers, onto some sort of variable-height trolley platform, something like an ambulance gurney. With enough design thought, the battery could be shifted without any lifting onto a small two-wheeled hand-trolley.

Once you have the battery on a trolley, it can be delivered to a private recharging point in the home or office, taking multiple trips if required. Owners can lease extra batteries so thay can have some on charge and some in the vehicle at all times. But the massive advantage of this system is not at home, but at service stations.

Being able to swap out a flat battery for a fully charged one makes 'refuelling' possible anywhere. Service stations can install charging units that take the flat batteries into a locked-off sorting and storage area and deliver replacements in seconds. The flat ones get recharged until needed by another customer, and the range of the vehicle becomes, effectively, unlimited

The benefits continue: Leasing batteries and replacing them at self-serve service stations means that their age is no longer an issue. When they get old they can be taken out of circulation and recycled. Furthermore it offers future-proofing. As new battery technology becomes available, it can simply be rolled out to the service stations, slowly increasing the power storage capacity of the vehicle and its range. What other car technology could offer the possibility of improving performance over time? The service stations can also serve (more practically than private homes) as buffer systems for the electricity network, absorbing changes to a supply increasingly dominated by renewables.

The concept requires certain standards. Every battery pack needs to be the same size and shape, with the same connectors, handles etc. These cannot be changed after the system gains momentum, so they have to be very well designed. If different versions restrict configurations, such that every pack in a car (including the reserve, perhaps) has to be of the same version, then this will lead to unnecessary complications, so the in-car technology must be able to cope with batteries of different types, performances and capacities.

Overall I think the concept needs to be studied very carefully by the car companies, and adopted across the industry to help accelerate the switch from liquid fuels to electric. The continued importance of service stations for refuelling and the relatively cheap technology required for storing and slow-charging leased batteries will remove the opposition of the station owners (the oil companies) to the loss of revenue that the switch represents, and the removal of the twin challenges of range and refuelling will accelerate the take-up of electric cars


A company called Better Place are proposing something similar, although in their case they appear to want to automate everything and work with multiple sizes and makes of battery, replacing the whole thing rather than standard units. They have a MOU with Renault Nissan, so already have the first element of support they will need. I think they need to consider making the standard criteria 'man-portable' to allow people to charge the batteries away from the street.

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