A transition to electric cars isn’t just a matter of the cars, but also of the infrastructure that goes with them, including public charging stations. The Electric Power Research Institute and the Tennessee Valley Authority plan to cut the ribbon on Tuesday on a prototype of a new kind of charging station, one that uses solar cells and batteries. But they do not work together in quite the way the public might expect.
The initial installation has six parking stalls, one of them extra wide for handicapped drivers, with carport roofs covered with solar panels. There are three refrigerator-size battery packs in a building that is heated and air-conditioned.
Under the program, called the TVA Smart Station Initiative, such charging stations are described as “solar assisted” because the panels generate only 12 kilowatts at noon on a sunny day, and the charging stations, when in use, draw 3.3 kilowatts for each vehicle, for a total of nearly 20 kilowatts. Cars will go three or four miles on a kilowatt-hour, and in Tennessee, where all of the charging stations will be installed, the cells atop each space will make enough electricity to move a car about 7,000 miles a year, according to John W. Halliwell, a senior project manager at the institute’s research center in Knoxville.
Yet for much of the time, electricity from the cells will flow to the grid because no car will be there to charge. And to recharge the cars, the system draws power from the grid, so the sun does not have to be shining for a driver to charge up.
The batteries and the solar cells themselves are something like shock absorbers for the grid. If drivers want to charge their cars during peak periods on the grid, the charging station’s batteries will meet part of that demand so that the impact on the grid is milder. Likewise, the solar cells will chip in with some energy, lessening the load on the grid.
“If with new technologies we can control these resources on the distribution side, we can eliminate the need for potentially very expensive upgrades to the distribution system,” said James A. Ellis, the senior manager for transportation and infrastructure at the T.V.A.’s Technology Innovation Organization.
At the Electric Power Research Institute, which will be the site of the first charging stations, Mr. Halliwell said, the various elements could be used in any mix. The batteries, of an advanced lead-acid design, have a usable capacity of 30 kilowatt-hours. They will wear out if they get too hot and will not deliver much current if they get too cold, so one question is how much energy it will take to keep them at a comfortable temperature.
Years from now, Mr. Ellis said, batteries that began their life in electric cars but have lost some of their capacity might be suitable for use at the charging stations. In fact, one function of this program is to determine whether such batteries could be useful, although the batteries to be used in the initial trial are not the sort used in cars.
Researchers say they need to know a lot more about charging stations. Will drivers use them to get a full charge or simply park there for as long as they happen to be in the neighborhood, to add a few miles of range? (At 3.3 kilowatts, a typical car would add about 10 miles of range per hour of charging time.) Where are charging stations most likely to get used? Airports? Universities? Shopping center parking lots?
With the Chevy Volt hybrid and the Nissan Leaf all-electric vehicle just hitting the streets, the question remains open.
Another question is economics: there is no mechanism at the moment for charging the driver for the electricity. Because the project is expected to cost $50,000 to $100,000 per space, some purpose beyond electricity sales will probably be needed to make it work, Mr. Halliwell said.
The institute and the T.V.A. hope to have about 125 parking stalls in place, most of them by the end of this year and mainly in the Knoxville, Nashville and Chattanooga areas.
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