The New York Times' Green blog has a story on a relatively affordable ($90/MWh) use of battery technology recently added to a subway system in Pennsylvania.
Cutting the Electric Bill with a Giant Battery - NYTimes.com
The battery system, which I wrote about last year, is allowing the trains to run a bit like Prius hybrids. When they slow down at a station, their motors turn into generators, converting torque into current. Before the battery bank was installed, some of that current was returned to the third rail; but if the voltage got too high, it was shunted instead into a giant electric heater under the train, which simply dissipated the energy as heat.Continue Reading at the New York Times' Green blog
Now the battery captures excess current, about 3.5 to 4 kilowatt-hours per train that stops, and puts it back on the line when a train is accelerating.
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