Getting a Charge Out of Roads

The future of electric vehicles could soon come charging down the road – in more ways than one – with composites playing a key role. At a Logan, Utah, test track, researchers from Utah State University are exploiting the strength and wireless transparency of GFRP while experimenting with recharging moving electric vehicles. The goal is to solve a problem that’s kept electric vehicles to a small fraction of total car, truck and bus sales despite some clear advantages. “An electric vehicle with a city-range battery is quite economical. The total cost of ownership is on the order of half that of an internal combustion engine vehicle,” says Regan Zane, a Utah State University electrical engineering professor and director of the Center for Sustainable Electrified Transportation (SELECT), which manages the quarter-mile test track. “But that vehicle won’t meet your needs unless it can get you from city to city.” Some batteries in high-end electric vehicles, such as the Tesla Roadster, remain charged for more than 200 miles. But the average electric vehicle can only travel 40 to 100 miles on a single charge. Plus, a complete charge can take several hours. Studies and modeling show that more than 80 percent of the time, drivers travel less than 40 miles, Zane says. That makes an inexpensive electric vehicle practical – most of the time. Those occasions when drivers need to travel further distances could be better handled if there was some way to recharge the battery periodically while in transit. That’s why researchers at Utah State are looking at in-road, wireless recharging. There are a variety of ways this could be done. One is to bury the recharger in a trench under the road, which protects people from potential exposure to high voltage electricity. It also enables recharging independent of the weather and results in a roadway that doesn’t look much different than a standard one. Wireless recharging can be accomplished via electric fields, magnetic fields or a combination of both. Faculty at Utah State are experimenting with a magnetic approach at the test track, while faculty at SELECT partner University of Colorado Boulder are evaluating capacitive coupling with electric fields. According to Zane, the test track needed a material for trench covers that was transparent to any of the wireless recharging options housed below the track. The trench covers also had to be strong, since many tons of metal would routinely roll across them. Finally, trench covers had to be easy to remove so that the recharging systems could be changed out between experiments. Given these requirements, the Utah State researchers opted for DURAGRID^® pultruded GFRP bar gratings from Strongwell Corporation, headquartered in Bristol, Va. The gratings, which won one of the Awards for Composites Excellence (ACE) at CAMX 2015, feature a polyester resin reinforced with longitudinal glass roving and multidirectional glass mat. The grating is heat cured, with bearing bars and cross-rods first pultruded and then assembled into the final shape. A standard rectangular shape wouldn’t work because the grating had to cover an oval track. The bearing bars and cross-rods were custom fabricated to fit the contour. “Additionally, it’s not your standard grating that you or I might walk on,” says Barry Myers, marketing manager for Strongwell. The application uses DURAGRID HD-4000, a heavy duty version of the grating. “It’s a much heavier and thicker bearing bar that’s actually 2½ inches thick to be able to support vehicle traffic without a problem,” Myers says. He adds that the composite grating doesn’t interfere with cellular and radio frequencies, which is important not only in wireless recharging, but also in wireless communication. In the testing program at the Utah State facility, half of the track will provide wireless recharging. As vehicles travel around the track, researchers will evaluate how well a given recharging approach works. The eventual goal is to deploy a system that pumps in a tiny bit of electricity each time a car passes over a recharging zone. The dwell time over each recharger might only be fractions of a second, and it’s likely that the energy imparted might only be just a bit more than what is consumed moving between one recharger and the next. Over time and hundreds of miles, though, an electrified road could completely top off a battery, Zane says. As for the future, one thought is to develop recharger modules that can be buried when new roads are poured. This option would be akin to putting in piping and wiring that currently goes in with new road construction. Composites might be used in the structure to hold coils and other parts of the recharging system in the right position while providing protection against asphalt or concrete and offering the necessary electromagnetic transparency, Zane says. In other situations, the current setup on the Utah State test track might be replicated. Real estate in a city’s downtown is expensive and shutting down traffic costly, so tearing up the road to bury an inexpensive module might not be the most cost-effective approach. A better option would be an installation method that minimizes disruption. “In those areas it might make sense to have something like this GFRP grate that gives you easy access,” Zane says. It likely will be years before demonstration projects are put into place, he says. Possible initial locations include shipping ports and airports, where vehicle fleets and roadways are closely controlled. This project is just one step on the road to an expansive use of electric vehicles.