A Break Through For Electric Cars?

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June 23, 12:51 PM

by John Ryden, Global Warming Examiner

 

 

The major constraint to more widespread production and use of fuel saving electric cars has been the battery technology. Current battery technology is just barely able to produce a usable car. The batteries cost too much, don’t have a long enough service life, or have safety problems. Companies are working very hard to produce better batteries to make electric cars more available and more affordable. General Motors hopes to start limited production of their Chevy Volt Plug-in Electric Hybrid in 2010. That is the earliest they expect acceptable batteries to become available.

Improving battery technology will probably happen as design and manufacturing processes are improved. But it seems like a very slow process of small incremental improvements.

There is one company that is approaching the battery problem in a totally different way. They are developing a high performance capacitor that they hope will provide twice the energy storage of a lithium ion battery. That company is EEStor based in Cedar Park, Texas.

Capacitors have many advantages for storing electricity. They store electric power as a charge between two metal plates separated by a dielectric film. Capacitors are solid state devices, which mean there are no chemical changes like in a battery. The number of times the device can be cycled should be virtually unlimited. They can be very efficient at storing power because there is very little heat generated when charging or discharging the device. This means they can be charged or discharged very fast.

The problem with existing capacitors is that they are relatively big and very expensive. The formula for determining the stored energy in a capacitor is:

E = (C * V²) / 2

E = Energy in Joules

C = Capacitance in Farads

V = Voltage

Most capacitors work at relatively low voltages around 2.7 volts. One gallon of gasoline has the effective energy equivalent of 12.7 KWH or 44.8 MJ (million Joules). At 2.7 volts, it would take about 12 million farads of capacitance at about $10 per farad to create a capacitor that would replace one gallon of gasoline.

EEStor’s answer to the problem is to raise the voltage in the capacitor. At 400 volts, they would only need 560 Farads of capacitance to store the 12.7 MWH of power. (I do not know what voltage they will actually use and picked 400 volts for comparison purposes.) Notice that the storage capacity goes up geometrically with the increase in voltage.

The problem with raising the voltage is in the thin dielectric layer that separates the metal plates that hold the charge. Higher voltages cause leakage of electrons through the thin layer between the plates. That is why most existing capacitors use low voltages. EEstor claims they have discovered a material; barium titanate powder, that they use to plug holes in a ceramic separator that produces capacitors with extremely high permittivity, or ability to hold an electric charge without leaking. This allows them to use very high voltages, thus achieving a very large storage capacity with a small, less expensive device.

EEStor hopes to be able to produce electric storage devices that can hold more charge by weight than lithium ion batteries. They also hope to produce these storage devices cheaper. That would be a phenomenal break-through. EEStor was supposed to have these devices on the market already, but has pushed back the delivery date. Reading between the lines on their announcements, it seems to me that they have demonstrated that the technology works, but are having engineering challenges in moving the technology from the lab to commercial production. I wish them well in overcoming their challenges as their device could fast make electric and hybrid electric cars a reality. Large numbers of electric and hybrid electric cars on our roads replacing traditional cars would greatly reduce of demand for oil and have a very positive impact on global warming.

EEStor is a private development stage company funded by the venture capital firm: Kleiner Perkins Caufield & Byers. They also have an equity investment from Zenn Motor Company, which is a public company. Zenn plans to use the EEStor device in its electric cars. Zenn currently makes an electric car that uses lead-acid batteries. Their car has a range of 30 to 50 miles with a top speed of 25 mph.

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