Metro explores new green energy options: placing a wind turbine in a subway tunnel

Photos: Evan Rosenberg/Metro

You’re standing on a subway station platform, waiting for the train. Suddenly, the wind picks up. You know this means the train is coming. Many of you may also know why there’s wind: it’s displaced air being pushed through the tunnel by the fast moving train. And some of you — including Tom Kefalas, Metro Environmental Compliance and Services Manager — may have wondered if there was a way all that generated wind could be utilized as a renewable energy source.

Thanks to Tom Kefalas and Cris Liban, Director of Metro Environmental Compliance Services, we now know the answer is yes. From August through September 2013, Metro conducted a one-month pilot program to see if wind energy could safely and effectively be captured and used. The project involved working with engineers from WWT Tunnel, LLC, a subcontractor to Arcadis U.S., to create and install a unique 10-foot multi-blade mass airflow collection equipment (MACE) in the Red Line tunnel. To our knowledge, this is the first time a transit agency has tested the effect of having a wind turbine in a subway tunnel.

The MACE was installed between the North Hollywood and Universal City stations, a segment of the tunnel that sees trains reaching speeds of up to 70 mph. Each time a train left the station, the MACE fan blades would start spinning, thus capturing energy up to a minute before the train actually passed by. The blades would continue to spin up to 2 minutes after the train passed, and exceeded 1,070 revolutions per minute (RPM). The amount of electricity produced by these train initiated events was nearly double the amount that had originally been anticipated.

During the run of the pilot program, the MACE generated an average of 77.7 kilowatt hours (kWh) per day. It is projected that the 10-foot MACE section could generate more than 28,000 kWh per year–enough to power about 12 homes in California for one year, or turn out approximately $6,000 per year in electrical production.

In addition, a single 10-foot MACE unit could potentially help Metro avoid using electricity that would have generated more than 17 tons of CO2 emissions annually if created from natural gas, or more than 30 tons of CO2 emissions annually if created by a coal-powered plant.

This is great news for Metro as the agency strives to become ever greener. The MACE can safely and efficiently collect clean electrical power from wind that is already being produced by passing trains. Due to the regularity of the speed and schedule of Metro trains, the power generated is far more reliable than above-ground wind and solar power, and the electrical power generated can be used in various ways. It can be stored for use to avoid power spikes in usage during flex alerts or high demand periods. In AC format, the power could also be stored and used to provide power for electric vehicle charging stations, station and tunnel lights, escalators and more. And because the project is entirely underground, no CEQA environmental clearance process was required.

Since the end of the pilot program, Metro staff has been analyzing the data captured. Over the next year, Metro staff will follow up with a report evaluating the best use of MACE generated power and the feasibility of installing MACE into existing and new rail line tunnels.

All current trademarks and patents are currently held by MACE Energy Inc.

28 replies

  1. The wind you are harvesting here is caused by the fact that a train moving through a tight tunnel is highly unaerodynamic. The train car’s tight fit to the tunnel forces air to move in front of the the train rather than passing around it. This increases the energy required to drive the train forward.

    Has Metro (or any other transit agency) looked at ways to reduce the drag on cars through passive design features in the tunnels that would allow them to pass more efficiently through the air? Perhaps bypass air vents that allow the air trapped in front of a moving train to pass around behind it more smoothly. This would reduce the initial energy usage instead of just trying to recapture some percentage of it after the fact.

    That all said, it is exciting to see Metro think creatively about increasing efficiency. If a final version of the device could be developed that is low cost it could be a great retro fit for huge numbers of similar tunnels aroune the world.


  2. Em I is correct. This is a foolish waste of money. But I must give KUDOs to the turbine salesperson for rewriting the Law of Conservation of Energy! As far as publishing an article on this, well… it was very nicely written.