Wednesday, November 04, 2009

EEstor Comment

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EEstor Comment


I received an interesting comment on the EEstor ultracapacitor, which pointed out that if the thing actually works, there would be still some problems regarding charging times for electric cars.


Comment from Craig:

Tony,
Whether the ultracapacitors every materialize as cheap units for small consumer electronics remains to be seen, but they will not provide the dream of a quick refill that you envisage.

The problem is common to all electric cars:
Petrol has an energy density of about 10kWh/kg ~ 12kWh/litre.
A 60 litre fuel tank will hold 800kWh of energy, which is approximately 3GJoules.
Say a refill takes 5 minutes=300seconds (a quick coffee!).
The energy flux is now 3GJ/300s=10MW !!
The problem is not whether the battery can hold the charge (although this is an issue) but that the infrastructure to provide the flow of energy is very significant. That's why I don't think people will willing give up liquid fuels for transport!

Thank you for your informed comment Craig. I would be coming from a nuts and bolts background myself I did a few simple calculations. The EEstor example is given for a 52Kw/h capacitor/battery. As far as I know, these units (if for real) are supposed to work at high voltages.

If we take an operating voltage of say 2000 volts and a capacity of 52Kw/h it would take 26 amps of current 1 hour to charge the battery. 130 amps of current would do the job in 10 minutes. 260 amps would do it in 5 minutes.

Granted, these voltages and currents would present some problems but it would not be impossible to create an infrastructure to accommodate perhaps a less ambitious target of say 15 minutes.

IMHO It is not a question of choice regarding liquid fuels - we simply will have to consider a radically different approach. It may indeed not be ultracapacitors, but for sure carbon based fuels will need to eventually be phased out completely.



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2 comments:

bob said...

There is also the possibility of trickle charging a similar energy unit at home (or a public facility) and topping up from that when it is convenient. The home unit would be perfect for storing energy from renewables like wind and solar. It could also serve a role in grid load balancing, as could public facilities. Finally, the ultracapacitor would be an excellent energy source for instant hot water heaters. This application alone would result in a significant decrease in national power demand.
As for transferring energy from a home ultracapacitor to one in your car, it is all a question of amp rating. Off the shelf IEC60309 plugs are rated up to 125A. You would need several times that, but then the process could (and most likely) would be DC. This significantly simplifies the transmission design problems.
I would suggest that if Eestor or others are successful, it is likely we will see the end of people using gas stations as they do today. After all, why would you go to a gas station if you didn't need gas?

Jeronimo said...

A station has a high capacity EESU or bank of EESUs charging from the power grid. I drive my vehicle up and move the charge from their bank to my own. How thick is a gas pump hose? How many amps could you push through an electric cable the same thickness? Seems like a simple implementation using existing infrastructure. I'd wait 5 minutes to recharge if it cut my "fuel" cost from $50 to $5.