EEStor, an energy storage company, has kept electric vehicle enthusiasts on their toes with claims that it can build a very dense ultracapacitor, a potentially disruptive technology that could beat out conventional chemical batteries in many applications. But EEStor has been famously silent about the details of its device, leading some technology prognosticators and experts to doubt the product's existence. Last week, however, the low-profile company was awarded a patent for its methods, and with the patent came some juicy details.

According to the patent application (pdf), the energy storage unit can hold at least 52 kilowatt-hours of electrical energy, weighs about 282 pounds, and recharges in 6 minutes or less. By comparison, a lithium-ion battery storing the same amount of energy weighs more than double that and recharges in 6 hours.

An ultracapacitor-style energy storage device offers a wide range of improvements on existing battery technology. Toxic materials, short lifespans, an underwhelming ratio of power to size, and price are only a few of the problems that EV makers have to juggle in deciding on a battery chemistry. Add to that long recharge times and the explosive nature of lithium batteries (arguably the most promising battery chemistry for cars), and the field looks cluttered with mediocrity. EEStor's devices, by contrast, are made from conventional, safe, and non-toxic materials—basically a titanium powder, copper, plastic, and aluminum—which means they'll have low production costs. Capacitors also don't wear out the way that batteries do, so they ought to have much longer lifetimes.

Despite EEStor's extreme reticence, the company has landed agreements with Zenn Motors, to incorporate the capacitors into Zenn’s electric vehicles, and Lockheed Martin, which is pursuing defense applications for the devices. And it's not alone in the field—millions of ultracapacitors currently provide backup power for the memory used in microcomputers and cellphones. They supply brief bursts of energy to numerous consumer products containing batteries, for example by powering the zoom in many cameras. They're also being used in subways to recapture energy vehicles lose during braking.

But scaling up from cameras to cars is no easy feat. Whereas batteries release energy through a chemical reaction, ultracapacitors (also called supercapacitors) are essentially larger versions of the most mundane component in electrical engineering, the common capacitor. A capacitor, which consists of two electrode plates separated by a piece of material, stores energy in an electric field on the surface of the plates. Storing more energy tends to mean increasing the size of the plates, and therefore the size of the device. Making a high-energy capacitor that can fit into a vehicle and leave room for the rest of a car's guts has been an ongoing challenge—until now, perhaps.

Beyond electric vehicles, ultracapacitors could also significantly improve the case for grid-connected renewable energy systems. The grid works best when electricity flow is constant and predictable, so utilities that incorporate solar and wind power need a way to smooth out the bumps in electricity availability that can appear and disappear with the whims of weather. Grid operators currently use a number of energy storage techniques, none of which perform the task all that elegantly. Banks of energy-dense ultracapacitors could be one solution.

This article originally appeared in "Plenty" in December 2008.

Copyright Environ Press 2008