Skip to Content

Ultrahybrid

Transportation
September 1, 2001

When General Motors’ electric buses hit New York City’s streets for a test run a couple of years ago, the company found that the new hybrid vehicles-propelled by a diesel generator and electric motors-burned less than half the fuel of a conventional diesel and created 90 percent less pollution. One hitch: the roughly 5,000 dollars’ worth of batteries that mediated the flow of electricity between the generator and motor burned out after only a year. Now, GM plans to keep its hybrid buses rolling by replacing the batteries with a high-tech cousin of the capacitors that regulate power in electronic devices. The same technology may soon help make hybrid cars more efficient and affordable.

Unlike batteries, which store energy using chemical reactions, capacitors store power as static electricity-and so can charge and fire millions of times without wear. The ultracapacitors in GM’s new buses outpunch garden-variety capacitors by incorporating carbon electrodes riddled with pores and fissures. Each gram of carbon provides thousands of square meters of surface area; more surface area means more charge can be stored. Ultracapacitors also charge in a flash-which could boost fuel efficiency another 10 to 15 percent, says Andrew Burke, director of the University of California, Davis’s Electric Vehicle Power Systems Laboratory. That’s because a hybrid recovers short bursts of energy each time a driver brakes. Whereas batteries can capture only 60 percent of a vehicle’s braking energy, ultracapacitors grab over 95 percent. According to GM, swapping the new hybrids for the 13,000 transit buses that serve the top nine U.S. cities would save nearly 950,000 barrels of diesel fuel each year.

GM says PowerCache ultracapacitors from San Diego-based electronics manufacturer Maxwell Technologies will power its commercial hybrid buses, due to roll out in 2003. You might well find ultracapacitors under cars’ hoods soon after, Burke says, beginning with the pollution-busting “light hybrids” that GM, Ford Motor and other automakers plan to introduce in 2004. This new type of gas-electric hybrid has a high-voltage electrical system, allowing it to cut off the engine at each stoplight, then use an electric starter to jolt it back to life when you hit the gas. Ultracapacitors could deliver that jolt without wear, meaning light hybrids could soon burn rubber without burning out the battery.

Keep Reading

Most Popular

still from Embodied Intelligence video
still from Embodied Intelligence video

These weird virtual creatures evolve their bodies to solve problems

They show how intelligence and body plans are closely linked—and could unlock AI for robots.

conceptual illustration showing various women's faces being scanned
conceptual illustration showing various women's faces being scanned

A horrifying new AI app swaps women into porn videos with a click

Deepfake researchers have long feared the day this would arrive.

protein structures
protein structures

DeepMind says it will release the structure of every protein known to science

The company has already used its protein-folding AI, AlphaFold, to generate structures for the human proteome, as well as yeast, fruit flies, mice, and more.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.