By Tania Tauer
With a push of the blue button the car is raring to go. Yet all is quiet. There is no rev of the engine, no hum from the exhaust. As the car glides silently down the road, the battery packs deplete, but the car doesn’t die. Instead it shifts seamlessly to its gasoline-powered engine and the vehicle continues on its exceptionally smooth drive.
The electric-hybrid Chevy Volt offers a unique juxtaposition of old and new technology. Rechargeable batteries allow the hatchback to travel locally on stored electricity, while the dependable internal combustion engine acts as an ever-present backup system.
“It’s called an extended range vehicle. With a fully charged battery you can go 35 to 50 miles, but as soon as the batteries are down the gas motor kicks in and runs a generator that starts recharging the batteries,” explains Kirby Reynolds, a Chevy sales representative at Central Chevrolet in Denver, Colorado. He clarifies that the internal combustion engine never directly powers the car. Rather, it recharges the batteries as the electric motor continues to propel the vehicle.
With unpredictable fluctuations in gasoline prices and a growing desire to develop an energy independent nation, President Obama and the Department of Energy have set out to put one million electric vehicles (EVs) on the road by 2015. The Chevy Volt is just one of a handful of plug-in EVs that is taking to the streets over the next year to contribute towards this ambitious goal.
While reviews have been favorable for the newly released Volt, as well as the upcoming Nissan Leaf and Toyota plug-in hybrid Prius, electric vehicles have hit a few early road bumps. Safety concerns, battery inefficiencies, and infrastructure limitations have prompted doubts about the practicality of these alternative vehicles.
“There are so many problems,” says Seehee Lee, a mechanical engineering professor at the University of Colorado Boulder who has spent the last six years researching novel materials for lithium-ion batteries.
Safety is perhaps the most critical concern for today’s battery technology, particularly the potential for batteries to ignite. Recently, a report surfaced of a Chevy Volt battery bursting into flames and sparking a fire that engulfed the vehicle, three weeks after the National Highway Traffic Safety Administration performed a side-impact crash test and post-impact rollover test on the vehicle. Two of three subsequent tests to simulate the same damage resulted in fire. This prompted the NHTSA to open an investigation into the stability of lithium-ion batteries. While the NHTSA released a statement saying the safety agency does not want to imply that EVs, or specifically the Volt, are more at risk of catching fire than traditional gasoline-powered vehicles, the inquiry has heightened awareness about the imperfections of first generation EV batteries. Recently, Chevrolet announced it would modify and strengthen the Volt to further protect the battery from the chance of electrical fire happening after a severe side crash.
Lee explains that a primary safety concern surrounding battery technology is a dangerous process called thermal runaway. When not managed properly, the heat produced from the batteries can cause the reactions in the device to speed up. These reactions in turn create more heat, causing a cycle that continues until a threshold temperature is reached and the battery explodes.
Electric vehicle manufacturers control the dispelled heat from these reactions through very precise thermal management software and hardware to keep the battery packs cool. However, “quite a lot of energy from the battery pack, sometimes 20 percent of the total energy, is used for this temperature management,” according to Lee.
This is valuable energy that’s lost from powering the vehicle and it’s a fairly significant issue. That’s because the lithium-ion batteries that power electric vehicles have a relatively low energy density — a value that describes the amount of energy stored in a given volume of material. In fact, gasoline contains 65 times the amount of energy per kilogram than current EV batteries.
The high energy density of gasoline means that the fuel tank doesn’t have to occupy much of the car. The opposite is true of batteries.
“Some EVs can get high mileage, but half of the car has to be full of batteries,” Lee says. “That’s why energy density of the battery pack becomes so critical. If we can double up the energy, we can reduce the size of the battery, weight and volume,” he says. This in turn will increase the maximum distance these vehicles can travel.
Current EVs have a large spread of estimated vehicle ranges. While the hybrid Volt can travel up to 380 miles on a single charge and a full tank of gas, the all-electric Nissan Leaf can only go an estimated 72 miles before its batteries become depleted.
“If you bought the Nissan Leaf and tried to drive it from Boulder to Colorado Springs, you aren’t getting there,” says Reynolds, the Chevy sales rep.
While all-electric plug-in vehicles may not make the ideal road trip car, they are extremely convenient for short commutes and local travel, especially when sufficient infrastructure is in place to enable vehicle charging during errand stops or workdays.
William Brinkman, director of the Department of Energy’s Office of Science, is concerned about the lack of construction of such infrastructure. “The big challenge with [plug-in] electric vehicles is getting enough charging stations,” he told members of the CU Energy Club in early November.
But simply building charging stations is not going to be sufficient. First, city officials and energy companies must consider the potential impact of EV charging on the current electrical grid.
“[Boulder] is in a unique position to be able to do that because we have the smart grid system,” explains Joe Castro, the city of Boulder’s facility and fleet manager. Boulder’s smart grid employs two-way communications between electricity producers and consumers to help allocate power more efficiently.
Last March, Boulder became one of 24 cities worldwide to receive IBM’s Smarter Cities Challenge Grant. As part of the award top IBM experts visited Boulder, analyzed the grid, and recommended ways that Boulder could improve its system.
“One of their suggestions was in the area of plug-in hybrids,” Castro says. “Their recommendations in EV integration were to test smart grid charging, building infrastructure, and to test rate plans.”
Information that Boulder learns through this program can be applied to EV infrastructure development in other cities and could directly impact policy changes in the area of electric and hybrid vehicles. Although Boulder received only a fraction of the funding it initially asked for, city officials say they will put the money to good use. The city has partnered with a number of local companies to design charging stations that integrate solar photovoltaic (PV) energy, energy storage devices, and complex automation systems to limit stress on the electric grid.
“If you have enough penetration of EV charging, Xcel’s concern is that it may overload the power stations,” Castro says.
According to Xcel Energy spokesperson Michelle Aguayo, the company has analyzed a number of scenarios representing different levels of EV charging and found that electricity generation and transmission capabilities are sufficient for the time being. However, under the most aggressive scenario Xcel found that transformers could become stressed.
In a recent testimony given to the Colorado Public Utilities Commission, Xcel explained that, “multiple EVs on the same transformer could cause overloading. Consequences of overloading transformers include reducing the life of the transformer and unplanned outages due to the melting of the protective fuse.” While it could take years for this extreme scenario to be reached, Xcel continues to monitor transformer loading and other grid impacts resulting from EV charging.
With an inevitable increase in EV usage, all eyes will be on how well these alternative vehicles cope with current challenges. Despite some preliminary speed bumps, early indications point towards a promising future for electric vehicles. Last month, for example, the Chevy Volt received Motor Trend’s 2011 Car of the Year award, while also topping Consumer Reports’ latest owner-satisfaction survey.
While critics wonder whether it’s too early in the development of EVs to fully commit to an electric vehicle overhaul, many like Castro believe we must start planning for these alternative vehicles today. “The timing is right, now,” he says. “The vehicles will be arriving shortly…I only see the demand increasing.”
Tania is a fourth year PhD student in Chemical Engineering at CU-Boulder with an interest in renewable energy. Her graduate research focuses on the modeling of proton conducting materials for the development of battery and fuel cell devices. Tania holds a B.S. in Engineering Science from the University of Virginia. Besides writing and researching, she enjoys skiing, triathlons, and cooking.