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Subway Train Wheels: The Next Power Source?

RP Siegel | Monday September 19th, 2011 | 2 Comments

Think of how much energy it takes to stop a moving subway train as it screeches into each and every station along its route. Right now, that energy is mostly dissipated as heat and noise. Imagine being able to capture some of that energy so that it can be used again. That’s exactly what that Vycon, a California company, proposes to do with it in its Regen (short for regeneration) energy storage system. They call it “energy recycling.”

The technology is based on an idea that is over a thousand years old: the flywheel. Origins of the flywheel can be traced back to the eleventh century Andalusian agronomist Ibn Bassal who described a flywheel being used in a water wheel machine. The machine transfered mechanical energy from draft animals onto a wheel designed for pumping water.

The flywheel, which is always a fairly massive disk, utilizes Newton’s principle of inertia, which states that an object in motion remains in motion. This principal is one of the reasons the motion of a rotating machine smooths out. Flywheels are common in cars, generally used at the interface between the transmission and the engine where they smooth out the jerkiness of the power that comes from the pistons going up and down in the cylinders.

When coupled with magnets and coils of wire, flywheels can become electrical generators, like the ones attached to gas or steam or water turbines in most power plants.

The same principle is also used in regenerative braking, a feature that contributes to the excellent fuel economy found in most hybrid cars. With regenerative braking, instead of using brake pads and rotors to stop the car using friction, which generates heat, they use the wheels as generators. Magnets run through coils of wire attached to the car’s frame, so that instead of heat energy being transferred from the motion of the car, electrical energy is produced, which goes back into the battery where it can be used again to keep the car moving.

This is quite similar to what Vycon does with it’s Regen products, as this video shows:

The energy of the moving train is transferred to the flywheel, which can spin for a long time. Thus, energy is stored until it is needed, perhaps to get the same train moving again once passengers have loaded. According to the company, up to 90% of the energy can be recovered. This is a great way to generate savings, especially considering how many trains run every day in so many cities.

The idea of recapturing a train’s kinetic energy is not entirely new, but earlier systems only captured 30-50 percent of the energy and they were quite expensive. Other companies, such as Viridity Energy in Philadephia, are pursuing similar opportunities using large batteries.

But Vycon claims that flywheels are greener than batteries because they contain no dangerous chemicals, and they last longer.

What other opportunities are there? Anytime you have a large heavy object, either slowing down or being lowered from some height, significant mechanical energy is released. Generally it’s not recaptured in other words, being wasted. So Vycon is also looking at applying their technology to elevators and the large freight cranes that are used to load ships.

[Image credit: martinpalmer, Flickr]

RP Siegel, PE, is the co-author of the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water.  Like airplanes, we all leave behind a vapor trail. And though we can easily see others’, we rarely see our own.

Follow RP Siegel on Twitter.


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  • Nick Aster

    Very cool. Though I’m not sure it really should be called a “source of power”. Really, this is just making existing power much more efficient – still a critical thing.

  • http://BMHydro.com/ Guest

    There is an old market that is now in the process of renewing that this would be ideal for. The original settlers of the US came here and set up businesses in the North East because of cheap hydro power; they built sawmills, gristmills, snuffmills and direct mechanical attachment to turbines that were operating from the rivers and streams. Cheap oil replaced this energy. Cheap oil is gone.
    Micro hydro systems will emerge being more powerful systems than solar or wind. I have one powering my home that delivered 30,000 Kwh of useful energy last year. It is connected to both, my electrical system and my baseboard heating. Flywheels of the 6Kw on up will be useful to eliminate losses due to non utilization of all energy produced by these systems. It can therefore eliminate the need for net metering in a great many applications.