Next EV Anxiety: Cold Weather
If you wandered around the Society of Automotive Engineers’ annual trade show earlier this year, you would have seen a number of ideas aimed at cutting power consumption in electric vehicles. One development in that category was from a company called BetterFrost. It devised a more energy efficient windshield defroster. Instead of blasting the windshield with hot air, BetterFrost sends 200-to-400-V pulses about a microsecond long to windshields containing a silver-oxide or fluorine-tin-oxide layer that ordinarily blocks the sun to help keep car interiors cool. The pulses generate enough heat to melt the thin layer of frost directly touching the windshield so windshield wipers can break up and remove the rest. Because it only consumes about 5% of the energy old methods required, the new process is said to give a typical EV about 12 miles more range.
If you hang around online forums for EV owners or own one yourself, you’ll understand why developments like that from BetterFrost will probably fi nd eager buyers. Online EV forums typically host a lot of bellyaching about the lousy range and charging problems that go with cold weather. On a forum for owners of Jaguar I-Pace electric SUVs, for example, one owner discovered he only had a range of about 90 miles in cold weather though the SUV’s advertised range is 292 miles. He also fumed about his level-one charger (a charger powered from 120 Vac). It couldn’t provide enough juice in cold weather to even pre-warm the passenger compartment, let alone charge the EV battery. Other I-Pace owners chimed in to advise keeping average daily travels to under 30 miles in the winter if a level-one charger was all he had.
I’d be willing to bet the car dealer didn’t bring up these details in the showroom. But that EV owner shouldn’t have been too surprised with his cold weather problems. Testing by the U.S. Dept. of Energy has revealed that cold weather reduces EV range by an average of about 41%. About two-thirds of the extra energy consumed goes to heat the cabin. Of course, fuel economy drops for ordinary vehicles in cold weather as well, but not as much as for EVs. Fuel economy tests show that a conventional car’s gas mileage is roughly 15% lower at 20°F than at 77°F in city driving. It can drop by as much as 24% for short (three to four-mile) trips.
One reason EVs don’t do well as the temperature drops is that the battery electrolyte fluid becomes more sluggish. This slows down charging and reduces capacity. Additionally, to protect the battery, the EV onboard computer may limit how it’s used in extreme low temperatures. One reason: Fast charging can damage the battery when the thermometer is low. EV owner literature usually mentions such drawbacks but tends not to express them in graphic terms. The Tesla Model S owners manual, for example, advises: “In cold weather, some of the stored energy in the battery may not be available on your drive because the battery is too cold.”
Solid-state batteries now on the drawing boards will do away with liquid electrolyte and thus handle cold weather much more adeptly. But despite rosy predictions from a few battery start-ups, these improved cells are probably 10 years away. To tide over EV owners until their debut, the Dept. of Energy offers ideas on its web site about how to improve EV range in the cold. One of these suggestions is to park your car in a warmer place. We’d suggest Miami.
Leland Teschler • Executive Editor
Filed Under: DIGITAL ISSUES • DESIGN WORLD, DIGITAL ISSUES • EE WORLD
