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The Dilemma of Fast Charging of Electric Vehicles

People like to see a lifebelt by the local river even though they may never use it. They certainly do not want to pay for one though. It is like that with the fast charging of cars. We all want to charge our electric car in the blink of an eye. Indeed, we may be happy to pay through the nose for that electricity when we are far away if the only alternative is to walk home or at least be late for an appointment. Many companies now offer fast chargers for on-road vehicles though very few have been installed. For instance, Japan has only installed 80 across the whole country.

Challenges with fast chargers include the following


Fastest “SAE Level 3” charging stations give only ten times the speed for one hundred times the installed cost. This is because they cannot use the inverter in the vehicle because it is not powerful enough and they need extra safety measures. Although Nissan has offered fast chargers down to $10,000 or so that is at a huge loss, the costs of most fast charger designs being near to $65,000 at present in our opinion. The price premium goes even higher when they need a community transformer as a grid upgrade. On the positive side, Mark Duvall, Director, Electric Transportation and Energy Storage at the respected Electric Power Research Institute EPRI in the USA said at the recent Advanced Automotive battery Conference AABC in Orlando Florida that grid upgrade is not commonly required and, when it is, it is something that was going to be needed anyway and is just brought forward a bit.

There are options instead of grid upgrade. One can slow charge a large battery in the charging station as with the vanadium flow batteries in the UniCube. Here charging can even include solar power and/or a wind turbine to give complete independence from the grid. However, this does not cope with intensive use and there is a cost. Alternatively, load management is offered by Siemens and others to prevent overload when too many cars are charging. This can even happen at Level 2. However, customers can be inconvenienced by this. Then there is EPRI developing HF solid state transformers in fast chargers that work directly from the main grid.

Standards not fully agreed/adopted

The Society of Automotive Engineers and others are completing standards for fast charging of on-road vehicles. Although these may look very grand with a lightning bolt of up to 240 kW permitted, in many countries the permitted grid upgrades simply do not cope with this, there is a big cost and there are other issues such as possibly needing an attendant. In reality, the sweet spot for fast charging is 50-65 kW. Contrast that with the fact that, to mimic a gasoline station filling many vehicles in one minute or so you need 40MW.


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