Metro becomes first transit agency in U.S. to apply flywheel technology for rail energy savings

Metro officials met with representatives from the Federal Transit Administration and the National Renewable Energy Laboratory last week to review promising results of the agency’s first-of-a-kind use of flywheel technology to recycle power generated from rail cars.

Officials met at the Westlake/MacArthur Park Metro Red/Purple Line Station to see firsthand how the Wayside Energy Storage Substation works. The pilot project started in August and is now saving Metro up to 18 percent of the energy normally used to power subway trains entering and leaving the station. That, in turn, helps lower Metro’s electricity bills.

The project is managed by Metro’s Project Engineering Department and uses a state-of-the-art flywheel system built by Vycon of Cerritos. The brain of the system, which assures the precise control of the flow of power, was developed by Turner Engineering of Venice. Metro performed its installation in-house, without external contractors.

The system was therefore entirely developed and implemented with resources local to the Los Angeles County. It is estimated that Metro will eventually save approximately $100,000 per year in electricity costs because of the project.

A grant of $4.5 million was awarded to Metro by the FTA TIGGER (Transit Investments for Greenhouse Gas and Energy Reduction) grant program that helps transit agencies implement new strategies to cut greenhouse gas emissions and energy use for transit operations.

Here’s how it works. The trains have regenerative braking systems that create electricity as the train slows to a stop at the station. The flywheel is like a mechanical battery that stores energy in a kinetic form by rotating a heavy steel cylinder up to 20,000 rpm. In order to keep friction to a very minimum, the flywheel cylinders are kept in a vacuum chamber and in magnetic levitation. They are more reliable, cleaner and more efficient than chemical batteries.

That stored energy in the flywheel is then reapplied to the train’s propulsion system to help the acceleration of the same or other trains departing the station. During this pivotal high power, short discharge sequence, the flywheel’s stored electricity actually replaces power that would otherwise have come from the electric utility company and turned into heat in the train cars’ resistors.

The system consists of a flywheel-based substation with a two-megawatt power rating (pictured above) and approximately eight kilowatt-hours of energy per cycle. The system is ready to have its capacity extended to six megawatts to further increase its energy savings capabilities. Even though the costs of this initial prototype are somewhat high due to the development and research effort involved, the system is expected to save, in one year, enough energy to power an average household in California for about 100 years.

19 replies

    • Uh, no. This is based on the principle of dynamic braking: every electric motor (with the possible exception of certain types of stepping and/or AC motors) is, at least potentially, also a generator. Dynamic braking, which has been in use for many decades, is a system that turns the traction motors of an electric or diesel-electric locomotive, or a trolley, el, or subway car (or electric automobile), into generators when the train is slowing down and/or descending a hill. Even when the energy is discarded, rather than being harvested, it saves wear and tear on the friction braking components (shoes for wheel brakes, blocks for track brakes, or rotors and pads for disc brakes). Simple dynamic braking, as found on diesel-electric locomotives, simply wastes the energy in large resistor banks (and an electric fan to cool them), while fully-regenerative dynamic braking, as found on hybrid and all-electric automobiles, diesel-battery-electric locomotives, and some fully electrified railroads, feeds the power produced back into the battery pack or the power grid (or in this case, into a flywheel bank).

      It’s the electrical equivalent of load-balancing on cable car systems (street, funicular, or overhead): because the cars are spaced out so that there are roughly as many going up as there are going down, at any given time, the net energy that needs to be pumped into the cable by the winding machinery is kept at a minimum.

      As to the wind turbine idea, well, if the turbines could be rigged to ONLY be in the airstream ahead of cars that are slowing down for a station stop (when increased wind resistance would be a good thing), and to be moved COMPLETELY out of the way of those that are trying to accelerate or maintain speed, then that, too, could actually produce a net gain. But that is an awfully big “if,” and it presupposes that the energy needed to move the turbines is less than the energy they can harvest in such a system.

    • I don’t know that it’s fair to accuse them of attempting a perpetual motion machine. They correctly identified a source of moving air and tried to tap into it. Their grasp of physics was insufficient to identify the problem, but, it came from a good place.

      I would actually fault the sneering article you linked to more greatly. They speak to many experts, yet spend zero time or experts’ time on proposing an actual efficiency improvement. In particular, they casually address a long-standing problem with subway design: The flat-headed subway train moves through a narrow tunnel, needlessly wasting effort pushing a column of air in front of it. Why is this the same design used world-wide when it’s so clearly inefficient? And why did this author and some of his experts spend all their time sneering instead of proposing better alternatives? Do they really deserve any admiration for accomplishing just as much progress with their efforts as Metro (that being, zero)?

      Elon Musk’s Hyperloop is the only proposal I’ve seen for this problem, which is to drive the air column in front of the train backwards with an active wind turbine, effectively turning the lossy air column into a source of propulsion. There’s nothing stopping subway systems from implementing this same element of his design, without taking on the rest (evacuated tube, maglev, etc).

      Yet, strangely, no one in the world’s subway systems seems to be spending time exploring this. Why?

      • While the BART high speed transit system had some simple streamlining for its first trains, operated mostly in open air, it should be noted that subway designers worldwide count on that air movement in the tunnels for its ventilation. Long automobile tunnels, conversely, use huge, and expensive ventilation fans, not just because of engine exhaust fumes, but because the size ratio of the vehicles to the tunnel walls doesn’t do the job properly.

  1. I am a geek and I find this mind-blowing! This rocks and I hope more deployment leads to even more electric bill savings.

    …and here I thought flywheels were a thing of the cable-car past.

  2. I’m amazed why it’s taking so long to update the TAP website. It must be very, very, very low on Metro’s priority list despite it can be fixed in less than a month by any web designer.

  3. So, basically it is costing taxpayers $4,5 million to save $100,000 per year. This project has a 45 year breakeven payoff, assuming zero cost of capital, and that the things will actually last 45 years without needing additional money for repairs or upgrades. This is nothing but a boondoggle and public money is being wasted! You guys are actually proud of this? Do you not have an accountant working there????

    • The $4.5 million was a grant from the Feds, not a loan. Grant = money free to Metro. It is money that the Feds are investing in technologies designed to limit human emissions of CO2. Since this is a “first-of-a-kind”, it is more expensive. The next 10 should be cheaper, the next 100 after that, even cheaper. This money is going to LA county companies. If they become the defacto supplier to agencies around the country (or world), that will be a boost to LA.

      • There is no such thing as “free money.”

        Federal Grant = money that still comes from tax dollars.

      • @Paul C.
        I did not say that it was “free money”. I said that it was free to Metro. I know where the money comes from. BTW, it was already allocated http://www.fta.dot.gov/12351_11424.html
        Metro got a nice chunk of the total available for this project. This money would have otherwise gone to a different agency. Either it comes to LA or goes somewhere else. I am glad that Metro got this, because the City of LA has been dropping the ball on getting these types of grants (which are part of the overall stimulus package that followed the ‘great recession’.)

    • On the surface it DOES look like another feel-good boondoggle. How about a breakdown of how that $4.5M was used? If any was used on non-recurring, reusable engineering design or testing that would be a plus for the ROI.

      • What’s with the hatin’? You’re upset because tax money that you paid… came back to us? Do you honestly expect the mass transit infrastructure ramp-up for the second-largest city in America not to cost money and not to be willing to experiment? It’s productive research and development. That’s hearty and as American as you can get. They’re not disobeying the Laws of Thermodynamics — they’re learning from a live system.

  4. Is this the same sort of regenerative braking system that automakers have been starting to use in certain types of cars these days? I can imagine a massive subway train produces a whole lot more kinetic energy.

    Given the amount of savings you guys are getting, just imagine what it could do for cities with larger subway systems, like Washington DC or New York.

  5. My question would be whether that $100,000 per year in savings is only at the MacArthur Park station, or is that a system-wide savings? If it’s the latter, I sure hope it was only 4.5 million to develop the technology, and not 4.5 million to install at each station. I realize there are intangible benefits to using less energy, but at 50+ million to save $100,000 a year, there’d have to be a LOT of intangibles happening, y’know?

    The other question that occurs to me is – would it perhaps be simpler to just have the regenerative braking built into trains? Is it even feasible? They might have to carry some batteries, but perhaps it’d be worth it. If they can put it on a Prius, why not on a Kinkisharyo?

    • I think it is because dc railways often use a floating earth or traction earth which is different to mother earth. The two are kept separate to reduce stray current effects which damage steel structures. Thus the enclosures are probably connected to the traction earth for fault current detection and return purposes and not directly to the general ‘earth’ of other equipment in the room.

  6. This seems like a very promising technology working on a similar principle to a hybrid automobile. Of course Metro was right to take advantage of the grant. This technology should be more widely deployed to reduce greenhouse gas emissions from electricity generation and because it will result in Metro being able to operate its system at a lower long term cost. Efficiency is a beautiful thing.

  7. I am wondering whether this flywheel technology could also be used in light rail systems?