With a click and a hum, the sleek Porsche 914 pulled away from the curb while a dozen onlookers watched anxiously and the passenger gazed down at a laptop plugged into the dashboard.
Why the drama? Once powered by a conventional gasoline engine, the 1976 Porsche now operates on 18 high-tech batteries—the result of work by a group of dedicated undergraduate and graduate MIT students and their mentors.
Converting the car to an advanced electric vehicle (EV) is an achievement in itself and serves to demonstrate the viability of the technology. But for the students, the real fun starts now. Said mechanical engineering graduate student Craig Wildman, “Now we get to take data while we’re driving. We can record everything that happens on a laptop, come back and change parameters, and test drive it again.” With the Porsche as a test platform, the students can monitor conditions in the car while looking for ways to increase efficiency, performance, and range and to bring down costs.
The Porsche was donated two years ago by Professor Yang Shao-Horn of mechanical engineering, who with her husband, Dr. Quinn Horn, a consulting engineer from Exponent, bought it on eBay and made it available to students interested in converting it to electric power. In addition to providing an unusual opportunity for hands-on learning, the project will ultimately yield information valuable to Shao-Horn’s research on advanced batteries. Specifically, she and her colleagues in the MIT Electrochemical Energy Laboratory will be able to measure the conditions that batteries encounter inside an operating vehicle.
“In the laboratory we work on materials to make batteries safer, last longer, and have higher energy,” she said. “But we are also interested in gaining a good perspective on the system. What’s involved in building an electric vehicle, and what’s required of the batteries?”
The student project took off when Valence Technology, Inc., agreed to donate 18 rechargeable batteries valued at $2030 each, plus a battery-management system. While electric vehicles have generally operated on conventional lead-acid batteries, Valence provided its enabling lithium phosphate rechargeable batteries, which are lighter, last longer, charge up faster, have a longer lifetime, and don’t pose a safety risk.
Last year, Gerardo Jose la O’, a graduate student in materials science and engineering, Emmanuel Sin ’07, and others began the project by removing the original engine, exhaust lines, and fuel tank and installing an electric motor and motor controller, the batteries and battery-management system, a battery charger, and various smaller components. Each of the batteries is equipped with a built-in computer that monitors its conditions—ideal for the data-gathering task. However, getting all the computers to communicate with one another and with the battery-management system—a separate computer—proved a challenge. While the students had made great strides with a commercial converter kit, they ultimately had to scrap it because it was designed to handle 12 lead-acid batteries rather than 18 lithium ion batteries. They subsequently redesigned the wiring and reprogrammed both the motor controller and the battery controller—changes that should improve efficiency and range as well as safety.
The two test drives thus far have been confined to MIT parking lots, so serious data gathering is yet to come. In the meantime, Irene Berry, team leader and a graduate student in mechanical engineering and the Technology and Policy Program, has done some performance estimates with a vehicle modeling program she is using in her graduate research. According to the model, the Porsche should have a top speed of up to 100 miles per hour with an estimated range of 130 miles before the batteries need recharging—a task achieved by plugging it into a wall socket for four to five hours. The car should consume about 185 watt-hours per mile of electricity, which converts into more than 180 miles per gallon of gasoline equivalent—disregarding the electricity needed to charge the batteries. Accounting for the generation of that electricity—a more meaningful calculation—yields a full-cycle fuel economy of about 65 mpg of gasoline equivalent. (That result is based on the average grid efficiency used in calculating fuel economy for regulatory purposes by the U.S. Department of Energy.)
Last fall, the students involved in the project formalized their association: they became the MIT Electric Vehicle Team, co-sponsored by Shao-Horn’s lab and the Sloan Automotive Laboratory, where the Porsche is housed and the work done. Work on the car is supplemented by team meetings where members exchange information and discuss plans and design changes. According to Berry, “No one knows that much about the science and engineering of electric vehicles, so we take turns researching a topic and then presenting what we find out at the next team meeting.”
Team members are all big supporters of EVs, quick to enthuse about their technological advantages and market potential. For example, in place of the usual massive internal combustion engine, an EV has a flexible electric motor that has better torque characteristics and can with a flip of a switch go backwards, putting the car into reverse, no transmission needed. Fewer moving parts means less maintenance, lower costs, and less waste. Batteries—now the critical enabler—are constantly improving, and while the driving range is still limited, EVs can go far enough to meet a surprisingly large fraction of our needs. (One doesn’t need a truck that seats five and can tow a boat to go to the supermarket, noted Wildman.) Many auto manufacturers are displaying a growing interest in EVs, and graduates of the MIT EV Team will be well-positioned to contribute to their development and proliferation.
What’s next for the electric Porsche? One idea is to modify how the batteries are wired together. “We should be able to change our range and performance characteristics very easily,” said team member Josh Siegel, a first-year student who has been restoring cars in imaginative ways since he was 14. “That’s something that I think we’ll probably play with.”
A more immediate plan is to add regenerative braking—a method of raising efficiency by scavenging energy otherwise lost in braking as noise and heat. During deceleration, the motor acts as a generator, slowing the car, and generating electricity to recharge the battery. According to Berry, “Implementing regenerative braking on the Porsche will be a valuable design experience for our team, particularly optimizing regeneration and its interaction with the mechanical brakes while maintaining consistent brake feel.” The team’s work will serve to highlight the efficiency gains possible in production electric vehicles.
The students are also concerned about recharging their batteries using electricity from conventional power plants. Instead of relying on power from a wall socket, they’d like to see an approach that would use electricity from clean, renewable energy sources. “I think it’d be fantastic if we partnered with some of the solar researchers on campus to develop a solar EV charging station,” said Jeff McAulay, a first-year graduate student in MIT’s Technology and Policy Program and incoming vice-president of the MIT Energy Club.
Finally, the students are thinking about developing conversion guidelines that will enable others to do what they’ve done—without all the fuss. “In most places, you just can’t buy an electric car now,” noted McAulay. “But there may be a retrofit market. People who are tired of paying high gas prices or have an old car that they like but maybe the engine is shot could end up with a great all-electric commuting car.”
For more details about current team members, activities, and sponsors, the Porsche 914 project, and EVs in general, please visit the new Electric Vehicle Team website. Information about initial work on the Porsche can be found in Electric Conversion of Porsche 914, an undergraduate thesis written by Emmanuel J. Sin. The thesis was awarded the Peter Griffith Prize for an “outstanding experimental project and thesis” by the Department of Mechanical Engineering in May 2007.