State’s roads provide hope as renewable power source
California’s famously congested freeways may soon do more than create headaches.
State officials have agreed to fund an initiative to generate electrical power from traffic, a plan that involves harnessing road vibrations with the intent of turning the automobile, like the sun and wind, into a viable source of renewable energy.
The technology is peculiar but proven. Devices that convert mechanical force into electricity are used in watches and lighters and are being tested for power generation on sidewalks and runways. A San Francisco nightclub has even leveraged the pulses of a dance floor to
power its lights and music.
But it remains to be seen whether the science can be employed on a large scale — threaded beneath the state’s sprawling highway system and rigged to produce significant, cost-effective electricity.
“There’s a lot of traffic in California and a lot of vibration that just goes into the atmosphere as heat. We can capture that,” said Mike Gravely, a senior electrical engineer and head of the research division at the California Energy Commission. “The technology has been successfully demonstrated.”
Gravely helped draft the proposal approved Wednesday by the Energy Commission’s governing board, which will direct $2.3 million to two independent road projects designed to test the viability of scaling up piezoelectricity.
“Piezo” is Greek for “squeeze” or “press” and refers to using pressure to create power.
Both of the state’s pilot programs are expected, within two to three years, to be far enough along to give California officials an idea whether the effort should be expanded. By developing new technologies like piezoelectricity, the Energy Commission is looking to help meet the Legislature’s target of producing 50 percent of the state’s power from renewable sources by 2030.
“The ultimate goal for us is to move this to a commercially viable product,” Gravely said. “As you drive down the road to San Francisco, you’d see them on the side of the road. Just think about the Golden Gate Bridge and downtown traffic on Highway 101.”
The first demonstration is scheduled for the eastern edge of the UC Merced campus. Jian-Qiao Sun, a professor at the university’s engineering school who was awarded $1.3 million from the state, is designing a 200-foot stretch of asphalt that will be sowed with tiny piezoelectric generators.
The inch-wide devices will be stacked “like quarters” within numerous arrays beneath the pavement, where each will convert the force of passing cars into a small electrical charge. Taken together, Sun said, significant energy will be produced.
“You can imagine there will be two tracks of these things on the road, and the distance between them will be the length of a typical vehicle axis,” he said. “Eventually, we can put thousands of them on the road, in busy sections.”
The resulting electricity could be used to power nearby lights and signs, stored in batteries or sent to the grid, Sun said. The more traffic there is, and the heavier the vehicles are, the more power can be created. Some state estimates suggest that just 400 cars an hour would need to pass over the arrays to make them economically viable.
Such configurations have been tested in other parts of the world. However, there’s little consensus on how effective these efforts have been.
Perhaps the most publicized demonstration took place on an Israeli highway several years ago, when a startup company claimed success generating 150 kilowatts of electricity over a half-mile stretch of road, enough to power about 50 or so homes. The firm has since suspended its testing, though, and subsequent initiatives have showed varying results.
The California Energy Commission’s second piezoelectric project, which will be undertaken by the company Pyro-E in San Jose, is expected to build upon recent demonstrations with a design that would power up to 5,000 homes from a half-mile of highway.
The $1 million program will be similar to the UC Merced plan, embedding arrays for power generation in a test section of roadway. The company also intends to explore whether the technology could be used for data collection, recording traffic conditions and aiding navigation for self-driving cars.
“There’s a lot of options that we can do with these things beyond energy conversion,” said Kevin Lu, PyroE’s founder and president.
But not everyone is on board with plans to use California’s roads for more than driving. State legislation proposed six years ago that would have introduced similar highway power projects failed amid concern that the technology wouldn’t produce enough energy — and might damage critical freeways.
John Harvey, a professor of civil and environmental engineering at UC Davis who runs UC’s Pavement Research Center, said roads aren’t meant to vibrate. Encouraging them to do so, he said, requires cars to exert more energy, which may be negligible for any single vehicle but would cumulatively increase fuel consumption, and could compromise the integrity of the thoroughfare.
Having to cut into the street to install devices, he said, would also create problems.
“It just doesn’t pencil out,” Harvey said. “The state just passed a $5 billion (per year) tax measure to fix roads, and one of the main things we want to do with pavement to keep it lasting longer and costing less is not put stuff in it that is potentially going to shorten its life.”
The new test projects will evaluate any potential harm done to the roads, while studying whether the technology can compete economically with solar and wind power.
Mike Gatto, the former Southern California assemblyman who wrote the 2011 piezoelectric bill, said he thinks the demonstrations will show promise. Since he proposed the legislation, he noted, the science has progressed.
“Whenever you’re talking about a new technology, there’s always a bit of skepticism,” he said. “When the hippies said you could put silicone in the desert and get a charge from the sun, people were like, ‘Right, man.’ Now there’s solar power everywhere.”