SEPTA is putting the brakes — the El's brakes — on wasted energy

A lot of energy is wasted each time a train stops at one of the 28 stations on SEPTA's Market-Frankford Line.

In a six-car train, the brakes produce about 3 million watts of power during the 15 seconds it takes to halt the 400 tons of hurtling metal, plastic and humanity. Some of the electricity is reused by other trains on the line. Much of the power is lost — dissipated as hot air through the subway car's rooftop vents.

But what if the electricity produced by the train's regenerative brakes could be captured and reused, as it is with a hybrid vehicle? And what if the power could be resold at a profit?

That's what SEPTA and Viridity Energy, a Philadelphia smart-grid company, hope to accomplish. On Wednesday, the partners will formally launch a sophisticated battery-storage system to capture energy from the Market-Frankford El.

The Wayside Energy Storage Project, situated in Kensington, is generating a lot of excitement in energy-efficiency circles because it combines two concepts — reducing SEPTA's electric bill from Peco Energy Co., and selling stored energy back into regional power markets. It's all about the economics.

"By combining the two together, the return on investment goes up, and the payoff is much quicker." said Kevin Morelock, managing director of Viridity Energy.

SEPTA received a $900,000 grant from the Pennsylvania Energy Development Authority to prove the concept, which it hopes to replicate throughout the Market-Frankford Line. Viridity hopes the system, if it proves effective, can be reproduced in transit systems around the world.

Viridity estimates that the one-battery system alone will return more than $250,000 in total economic benefits a year.

SEPTA recently received a $1.5 million federal grant to build a second system. Andrew Gillespie, its chief power engineer, said the transit agency hopes the savings from the two units will fund the installation of up to 10 systems on the El, its busiest service.

"When the battery gets full, it discharges into the rails," said Gillespie. "When we do that, we are not buying power from Peco."

SEPTA aims to cut energy use 10 percent by 2015 and reduce greenhouse-gas emissions 5 percent a year. It currently spends about $20 million a year on electricity for its subways, trains and trolleys.

The project demonstrates the complexities of the "smart grid" system, where regional grid operators such as PJM Interconnection Inc. need to coordinate an increasingly scattered network of energy sources — solar panels, wind turbines, and small power generators — to maintain a delicate balance between supply and demand.

"It sounds like a simple concept, but it's actually very complicated to do, to control the system so we can participate in the wholesale market, at the same time we can capture the 're-gen' power," Gillespie said. "The two things have to work simultaneously. That's been the hardest thing to prove."

Just as a hybrid car recovers energy when it slows down, many electrified trains convert kinetic energy into electricity with regenerative brakes. On SEPTA's Market-Frankford Line, the power is put back into the third-rail system, for use by other trains.

The Wayside battery-storage project takes the concept one step further. By storing SEPTA's excess regenerated power in large battery systems, Viridity can control discharges to take advantage of PJM's fluctuating electricity markets.

SEPTA installed its battery system in a spare room at the Letterly Power Substation, a century-old brick building near the Huntingdon Station in Kensington.

The beauty of the system is hidden from view. Lithium-ion batteries, produced by Saft North America, are stacked in racks in a 20-foot white, refrigerated shipping container that has the visual appeal of a meat locker. The brains of the system, the switching and control equipment built by ABB Envitech, is housed in a beige metal cabinet. The two humming, unattended metal boxes are controlled remotely by Viridity personnel at 18th and Market Streets.

"On an average 65-degree day, electricity is probably selling for 10 cents a kilowatt," Gillespie said during a tour last week, when the temperatures had surpassed 90 degrees by 9 a.m. "You get a day like today, it could be selling at 25 cents a kilowatt. If you discharge your battery the right time, you could make 25 cents a kilowatt where you're only buying it for 10."

SEPTA also plans to participate in PJM's "frequency regulation market," which requires producers to add power to or subtract it from the grid on a moment's notice to ensure the system operates at a stable frequency. SEPTA's batteries, which can store up to 800 kilowatts, are well-suited to an instantaneous response.

Gillespie said SEPTA expects the one unit to reduce its power purchases by $90,000 to $150,000 a year, and to earn $75,000 to $250,000 a year by selling into PJM's energy markets. Viridity gets to keep 30 percent of the revenue from PJM, he said.

Viridity, which has worked with Drexel University and Thomas Jefferson University and its Center City hospital on energy-storage projects, is banking on the high visibility of the SEPTA project.

"There's a new generator in town," the company says in its promotional literature. "And it's pulling into a subway station near you."