Utility companies have long known how to capture the braking energy from electric trains, but they've usually found it difficult to get any large-scale benefits from such projects -- until now.
An energy storage project in Philadelphia promises to capture braking energy and provide a voltage boost for electric trains, while offering so-called "frequency regulation" for utilities. The companies behind the project hope that it will reduce the need for fossil fuel generation, thereby creating economic and environmental benefits. "The central aspect of the Philadelphia system is that it doesn't just do regenerative braking and power-assist," Jim McDowall, business development manager for Saft, told us. "It helps with the demand side of the equation."
The new system could help utilities use regenerative braking power more intelligently. In the past, regenerative braking energy from train motors was typically pushed back into the electric train's third rail, raising the voltage. When the voltage rose too high, however, excess energy was diverted through coils and dissipated as heat.
Saft's Max20 lithium-ion energy storage system can push power back into the third rail when system voltage drops. (Source: Saft)
The Recycled Energy and Optimization project takes a different approach. Using a dc/dc converter from Envitech Energy, it senses when track voltage is too high (about 800V). It then sucks DC power out of the third rail and pushes it into a giant lithium-ion battery pack provided by Saft, until it's needed. "When the third rail's voltage drops too low, they can bring the power out of the battery and then put it back in the third rail," McDowall said.
Saft's batteries are located in a substation that serves five or six stations on the Southeastern Pennsylvania Transportation Authority's (SEPTA's) electric elevated train line. Using lithium-ion batteries with a well-known nickel-cobalt-aluminum (NCA) chemistry, the substation offers about 1.5MW of charge and discharge capability. Saft employed a high-power (rather than high-energy) battery configuration, largely because big electric trains on the line can capture 3MW during a 15-second period.
The company's Max20 lithium-ion energy storage system is roughly equivalent in size to 280 Toyota Prius battery packs. It employs 290 modules, each with 14 cells rated at 30 A-h.
The big potential benefit of the new system, however, goes beyond its ability to capture braking energy. By employing software from Viridity Energy and piggybacking a frequency regulation signal atop the power flow information, the system can modulate the loads at the substation in response to signals from the grid operator. As a result, it can change the amount of power that gets fed into the substation, and therefore eliminate the need to dissipate excess power as heat. "So a megawatt of storage might displace a megawatt of fossil fuel generation," McDowall said. "That means less cost for the market and less cost for society."
Engineers who are part of the pilot project believe that strategy could provide a return on investment that wouldn't otherwise be available by simply capturing braking energy and pushing it back into the third rail. "If we can prove the value proposition, then other cities will look at this for their substations, as well," McDowall said. "This is a very high-visibility project."
Wow. Very cool idea and great application of energy storage technology. Also a great test case for other cities and rail systems. My big question is who is paying for this pilot? It's got to be very expensive and with funding so tight for infrastructure-type projects across the country, I'm assuming this owned by the private sector. What's the likelihood that something like this has legs for being applied to other rail systems?
It looks like the energy could be managed by controlling who is starting and who is stopping, who is going up hills and who is going down hills, etc. I didn't realize that they ever dumped energy. I just figured things balanced out as some trains were stopping or going down hill while others were starting or going up hill, etc. You would think that an intelligent scheduler could manage things such that energy storage was not needed.
I would think it would only take slight timing changes to keep the loads balanced to where you wouldn't have to dump energy, or store it.
This is a great use of technology to enhance efficiency. It seems like a trend. Large diesel locomotives have begun using hybrid technology as well. Similar to this idea, they capture energy generated during breaking to provide low latency energy for acceleration. Thus, the diesel engines can be used more efficiently.
As Beth asks, I wonder how much this costs. Of course, the real metric is the cost to benefit ratio. Even a costly battery is worth it if it saves money on electricity from the utility.
The ROI and EROI isn't going to be good with this system, battery though using lead or molten salt might be cost effective near stations.
GE is currently doing a molten salt hybrid train Loco that would be a better way.
The only reason the voltage might go too high is high resistance in the 3rd rail not able to pass the power along and train operators slowing the train too fast. Training the engineers would be more cost effective eliminating the problem.
In the Rockies trains were scheduled so when one was going down it's energy was used to run another up the mountain. They stopped that back when oil got so cheap.
Now we're talking! What a great practical use of wasted energy. Especially when going down hill with megatons of load! I hope there is a future for this energy and it doesn't continue to go to waste.
Now, how can we do the same with other big systems on a large scale? The problem is, I can't think of anything to compare with trains. They are unique in this way. Good luck to Saft.
To some degree, they are in unexplored territory here, tekochip. Although regenerative braking and power assist have been done, the concept of piggybacking frequency regulation on top of regenerative braking in an application like this is new. Over time, the pilot will tell them more about the ROI.
"An energy storage project in Philadelphia promises to capture braking energy and provide a voltage boost for electric trains"
Charles, what would be the amplitude of this barking energy. Since most of the components in braking systems are electro-hydraulic components, I feel that only a little amount of energy can be regenerate in normal course (Am not sure). But anyway regeneration or reusing the energy is the best part.
Warren, am totally agreeing to your concept. It's the time to think about energy conservation, regeneration and exploring natural energy sources. Even am thinking further about generating energy, while train runs through the track.
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