Chief Engineer-Power
Southeastern Pennsylvania Transportation Authority
Philadelphia, PA

We are going to install a half a megawatt lithium-ion battery in a traction power substation on SEPTA’s subway line.

This battery, capable of storing enough power to light up 120 households in a day, will be charged from the electricity generated from when the train brakes. We will store that electricity until another train comes by that wants to accelerate, and we’ll discharge that electricity into the system.

What makes our project unique is that we are using the battery to save electricity already, but getting paid to help the local power company keep a balance of its network—balancing supply with demand.

Our power company is our grid manager, controlling the flow of electricity from those who generate it to the end user.  By using the lithium-ion battery and going through Viridity Energy, we can coordinate with the power company to determine when to charge or discharge the battery in accordance with that company’s needs.  That company pays us because, by using our stored energy, it doesn’t have to repeatedly fire up an extra burner, which costs money, and then shut it down.

Plus, we received a TIGER grant from FTA to test a different storage technology; we’re currently asking people to propose their technologies, but we haven’t selected anything else.

We are the only ones using a battery to do both the capturing and storing of electrical energy used by braking trains—and participating in the energy market.

For public transportation, it’s a means of generating revenue. But it also makes the capture of regenerated braking power economically feasible. Without the battery, the extra energy would have to go through a resister bank and be burned off as heat because it would have no place to go. With the battery, we can store it and hold onto it until we’re ready to use it.

Other than taking up space (approximately 12 feet x 20 feet), I can’t think of any disadvantages.

From a positive point of view, we hope to reduce our energy consumption by at least 10 percent, which allows us to achieve our sustainability goals, and the revenue that’s generated allows us to fund projects like this. I’m hoping the money we generate from the second pilot will let us do two more. Ideally I’d like to have a battery in every one of my substations.