A.J. NesteBatteries at a station on a Philadelphia commuter line capture excess current when trains brake and store the power for use when a train accelerates.
A giant battery bank installed by the side of the Southeast Pennsylvania Transit Authority’s subway tracks a little over a month ago is saving about nine megawatt-hours of power a week, its manufacturer says, which is more electricity than the typical apartment-dweller uses in a year.
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.
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. Sometimes it does this for several trains at once.
The battery bank is also receiving signals every four seconds from the regional grid operator and either absorbing energy or giving it back to the grid to help balance supply and demand.
Until very recently, the solar industry was mainly concerned with getting a toehold in the production of electricity at a utility-level scale. Now a New Jersey company is looking for its niche in a different field — how to handle a system that is saturated with solar energy, sometimes enough to destabilize the electric grid.
The company, Petra Solar, has a highly visible product: it is under contract to supply 200,000 panels that Public Service Electric & Gas will attached to utility poles around New Jersey. Around 75,000 are already up.
About six feet wide and four feet high, the panels make 200 watts when in full sun, and newer models will make 225 watts, the company says. On a mild day, one could almost meet the needs of an entire house in the daytime; on a hot day, four or five would run a window air conditioner.
On the top side of the panel, the side angled toward the sun, is the obvious attention-getter, the polycrystalline solar cell. What is different is the electronics bolted to the bottom, which are meant to prevent a solar power overdose. They could turn out to be crucial, according to company executives.