Thursday, July 20, 2006

I have too much spare time.

So, with the news earlier about Tesla's electric car getting me all excited, I decided to look back in to EEstor's ultracapacitor (ESU) and see what I could figure out about the potential there.

Some basic stats: Tesla's car seems to run on about 1,000 pounds of lithium-ion batteries, according to their website. This takes up quite a bit of room and stores roughly 27kwh of electricity. The car gets a mile to every 100wh of electricity, hence the 250 mile range.

Now, according to EEstor's patent filing, their ESU product stores 56kwh, and weighs 400 lbs. Quite a difference, obviously. The patent filing gives the rough volume of the ESU (2005 cubic inches) but not the exact dimensions. All the same, we can make some basic conclusions.

The first is that if Tesla replaced their batteries with an ESU, they'd see a 60% weight saving (in the battery pack) and double their range, if not more. This would bring the car's range on a single charge to around 500 miles (800 kilometers, or more than 8 hours driving at Ontario's posted speed limits. This doesn't take in to account the lower weight, which would extend the range even further.) They'd also presumably see a major cost savings, if the estimates of EEstor's prices can be believed.

More interesting is the potential for Tesla's 2008 sedan. If they're currently designing a car assuming a similar battery load, then the ESU could be doubled, bringing the weight to 800 lbs, and still leave plenty of weight for the power electronics that are necessary for capacitors. (If anything, I would assume that Tesla would be planning for more batteries.)

If they can keep close to the 110wh-per-mile that the Roadster acheives, the Sedan could conceivably make close to 1,000 km on a single charge. At 150wh-per-mile, the 104kwh in 2 ESUs would get a car 590 miles (949 km) assuming 85% of the energy makes it to the wheels.

The remaining question for me is if 2 ESUs can fit in the space that the current battery pack does. 2000 cubic inches isn't huge, but I can't find numbers for the volume of Tesla's battery pack on their website. So it's hard to say whether there's room or not.The 2008 time frame for the Sedan model gives them some time to redesign for the ESU if EEstor's numbers pan out in the reported third-party testing this summer.

You know what would be nice? Driving down to Washington in an electric car to see President Gore inaugurated in January, 2009.


adam said...

2005 cubic inches works out to about 1'*1'*1' (with one dimension slightly larger - almost 14"). A quick search on fuel tanks for sedans showed a capacity of 90 litres, so I can't imagine that the ESU is taking up more space than that (not sure about the dimensions of a 90 litre gas tank). 27 Kwh at the ~450Wh/L of a Li-Ion battery puts the current power storage of the Tesla vehicle at around 60 litres, just for comparison. Not sure how one measures a battery in litres, but the energy density is 900-1900 joules/cm3 if you feel like converting that.

Of course, both methods benefit from the face that you get to ditch the gas tank itself, as well as the (relatively bulky) combustion engine. You could even have motors on the axles and do away with the transmission entirely, since the torque of an electric motor is much higher.

Plenty of room in there, I would think.

Anonymous said...

EESTOR is a mythical creature. If there would have been something to it, car companies would be lining up around the block and oil companies would stop investing tens of billions in search of new sources of oil.
Keep dreaming, but I suspect that this is scam.