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."
Thanks, Chuck. It would be interesting to know the results of some of those efforts and if they were abandoned, continued, or replaced with other attempts/technologies.
Warren, this is also a good idea, but moving this huge load over piezoelectric substance is feasible? What I meant is a different idea. Any way wheels are rotating, so some electro-mechanical mechanism to generate energy, which can used for the internal usages like lighting, working of a/c etc.
Thanks ttemple for the comments about the difficulties of heat harvesting. In the IT environment, there was a lot of talk about harvesting waste heat from data center equipment a few years back after the info came out about their high amounts of energy use, and about the proposed extension of Energy Star-type ratings to commercial equipment. So I was wondering about the in-plant solutions; larger-scale "solutions" like dragging icebergs around just sound ridiculously complex, not to say unwise from a climate standpoint.
I have seen cases where manufacturing plants effectively move "process heat" around to reclaim it. I have never seen it on a very meaningful scale, however. Even in the case where there is excess heat, and a demand for heat under the same roof there are difficulties moving the heat around. In the cases I am thinking of, heat pumps are involved in concentrating the energy enough to effectively move it from areas that are too hot to areas that are cool.
An example is an automotive plant that has heat treating ovens at one end, and space that needs heated in the winter at the other end of the building. They use heat pumps in the heat treat area to concentrate the energy, and pipe it to other areas of the building that reclaim the heat. I believe they also use some of the heat in other processes within the plant that need heat.
The issue with energy in the form of heat is the difficulty in transporting it to where it is needed. (A few hundred feet is one thing - miles is another) If it were easy, we wouldn't need fossil fuel to heat houses. There are always places on earth that are too hot, and other places that are too cold, so we would just move the heat where we want it. Unfortunately, the means does not currently exist to effectively do this. Attempts to drag icebergs around is about as close as we have come.
A mechanism to efficiently transport energy in the form of low grade heat would be a game changer for mankind.
Although I'm not personally aware of whether those efforts are ongoing in any particular application, Ann, I'm sure our readers are. It makes sense that it would be ongoing in a number of different industries.
Energy dissipated as heat is wasted all the time in mechanical and electronic systems. I'm curious about efforts to recapture that heat, which were being discussed a few years ago, for example, in server farms and various IT environments. Chuck, do you know if those efforts are still ongoing in any industry?
The trains that I have watched come into the local train station all brake MUCH faster than they accellerate as they leave. Most traffic brakes much harder than it accellerates, except for drag racers. Even circle track cars seem to brake much harder than they accellerate. Not because they must, but because they can. And the biggest limitation on regenerative braking is putting the energy someplace. I can draw about 700 amps from a standard car bettery for cranking, but putting 700 amps into it would cause a lot of damage after a short time, I am sure.
The accereration and regeneration amount is set by the motor specs and are the same in most cases, just reversed.
A123 batteries in a 150lb pack can put out, take back 450hp, 350kw. Most battery can charge at the same max rate of discharge.
Piezo isn't viable as it sucks power from the train as extra drag to make the rails move and not eff either so you get back probably 10% vs 50% in braking style regeneration after losses.
Panic stops are rare and frowned on as they rapidly wear the rails and make flat spots on the wheels so not a regen issue. Trains run the same thing day after day by the same people on the same track usually so surprises are rare.
Much of New England is electric and all going through NYC by law are.
If the US was smart they would nationalize the rails, upgrade them to electric and charge by the mile, weight givng credits to pay for buying the rails from former owners. A kind of interstate or the rails. The fiasco we have now of many hundreds of company lines and too few double, 2 way tracks has seriously effected our economy, shipping costs and time to get from one place to another.
You'd be surprised TJ. The container pictured is a high cube 20' unit. These containers can be up to 53' in length and can be utliized in a number of ways. My company does this type of integration in ISO containers:) I'v seen that unit up close, it's a good looking unit and some innovative technology
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