Beta

×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Tapping Subway Trains For Energy

Soulskill posted more than 2 years ago | from the make-them-pedal dept.

Power 229

An anonymous reader writes "Industrial flywheel manufacturer Vycon Energy believes that they can tap the immense amount of kinetic energy carried by moving subway trains to subsidize city power systems. Not only would this reduce emissions, but it would also help to avoid peak power emergencies. This energy could the be used to start the trains up again — a 10-car subway train in New York's system requires a jolt of three to four megawatts of power for 30 seconds to get up to cruising speed — that's enough energy to power 1,300 average U.S. homes."

cancel ×

229 comments

Sorry! There are no comments related to the filter you selected.

Isn't this an old idea? (1)

atari2600a (1892574) | more than 2 years ago | (#37300174)

I thought EV's have been using the flywheel braking trick for years now...

Re:Isn't this an old idea? (0)

atari2600a (1892574) | more than 2 years ago | (#37300206)

Mother fucker... http://en.wikipedia.org/wiki/Regenerative_braking [wikipedia.org] I'm fine with them proposing to retrofit an entire fleet of trains, but a press release like this really yells SLEASY OR FRAUD

Re:Isn't this an old idea? (-1)

Anonymous Coward | more than 2 years ago | (#37300552)

i fucked your mother. with my big black niggerdick. she couldn't get enough of it. she loves the cock. especially dis nigger cock.

Re:Isn't this an old idea? (4, Informative)

Anonymous Coward | more than 2 years ago | (#37300208)

That's not what this is about. It's about putting flywheels in the stations themselves. The energy put back into the 3rd rail is usually wasted since it would require another train to be close to the train braking. Since most trains are guaranteed to stop in a station, absorbing the electricity put back into the rail could be stored for when the train starts. Batteries are insufficient, so they're using flywheels.

This exact same thing comes up every few years on Slashdot. Look it up if you don't believe me.

Re:Isn't this an old idea? (1)

Z00L00K (682162) | more than 2 years ago | (#37300898)

That actually makes sense - why have the train carry the regeneration unit when it actually can feed it's excess energy back to the grid. Lighter trains means less losses.

But it's hardly a new idea to feed energy back to the grid.

Re:Isn't this an old idea? (3, Informative)

ScottyLad (44798) | more than 2 years ago | (#37300220)

Indeed, Regenerative Braking [wikipedia.org] has been around for years, and is in effective use around the world in various guises.

The original article reads more like a marketing shot from Vycon's PR department than a news bulletin.

Re:Isn't this an old idea? (2)

jijitus (1478465) | more than 2 years ago | (#37300308)

And it isn't even the coolest train-related article on that site. Check out the one on moving platforms [inhabitat.com]

Re:Isn't this an old idea? (2)

hedwards (940851) | more than 2 years ago | (#37300496)

That is interesting. I think the major problem there is figuring out how to keep trains going on schedule. The other issues should be a lot easier to solve.

Well, there's also the issue of idiots being torn to pieces when they try to get through the door at the last moment.

Sounds like a win-win. (3, Insightful)

causality (777677) | more than 2 years ago | (#37300562)

Well, there's also the issue of idiots being torn to pieces when they try to get through the door at the last moment.

It's okay. There are plenty more where those came from. PLENTY more.

Re:Isn't this an old idea? (2)

MichaelSmith (789609) | more than 2 years ago | (#37300440)

A better way would have been to build the stations at a shallower depth than the tracks between stations. That way kinetic energy can be stored as potential energy when stopped.

Re:Isn't this an old idea? (0)

Anonymous Coward | more than 2 years ago | (#37300524)

I remember reading about a city doing this, maybe Boston?

Re:Isn't this an old idea? (0)

Anonymous Coward | more than 2 years ago | (#37300642)

http://en.wikipedia.org/wiki/Victoria_line [wikipedia.org]

The line has hump-backed stations which allow trains to store gravitational potential energy as they slow down and release it when they leave a station. This provides an energy saving of 5% and makes the trains run 9% faster.

Re:Isn't this an old idea? (1)

kanweg (771128) | more than 2 years ago | (#37300906)

Next step: Put the trains in vacuum tubes and use magnets to levitate the trains above tracks, and the trains can move around while hardly using any energy.

Bert

Re:Isn't this an old idea? (1)

errhuman (2226852) | more than 2 years ago | (#37300752)

They do this in the HK MTR system.

Re:Isn't this an old idea? (1)

FooAtWFU (699187) | more than 2 years ago | (#37300908)

And they're doing this on the new Second Avenue Subway in New York City, as well.

Re:Isn't this an old idea? (1)

zippthorne (748122) | more than 2 years ago | (#37300634)

Ahh yes, the ol, brachistochrone railroad [google.com] technique.

Re:Isn't this an old idea? (-1)

Anonymous Coward | more than 2 years ago | (#37300722)

Ahh yes, the ol, brachistochrone railroad [google.com] technique.

Ain't that cute, someone just learned how to Google for a term. He put two and two together all by himself. Awww, he's like a widdle walking rewerse dictionary. So enthusiastic to share his new discovery!

Re:Isn't this an old idea? (1)

ryanov (193048) | more than 2 years ago | (#37300810)

Many stations in New York are already like that.

Re:Isn't this an old idea? (1)

morethanapapercert (749527) | more than 2 years ago | (#37300858)

As others have mentioned, that's been done. I just have a couple of thoughts to throw out there:

1) I think it'd be pretty expensive and enormously disruptive to raise existing track at the stations along with the stations themselves. Adding a flywheel system, either under the platform or in the service area at the end of the platform would be a lot easier.

2) In some cities, the track at the stations is actually lower than the main line because the station had to be squeezed in under existing buildings or the below ground infrastructure.

3)In some cities the main track has to deal with enough changes in elevation as it is; enough, I suspect to negate the benefits of elevated track at the stations. The Bloor-Danforth line rises up out of the Don River valley quite a ways before it meets up with the Scarborough RT. IIRC from my local history class; that line was mostly done with the cut and cover method, which is much cheaper, as long as you follow the surface terrain loosely, otherwise some areas the trenches get impractically deep. (which is why some of the line was tunneled)

Re:Isn't this an old idea? (3, Informative)

brusk (135896) | more than 2 years ago | (#37300222)

It seems a little different. TFA is quite vague about how they are actually putting the energy into the flywheel. It says the wheel would be "housed in the station," but what that means is unclear. Does the train somehow mechanically transfer its kinetic energy to the flywheel? Or use hybrid/EV-style regenerative braking to generate electricity which spins the flywheel which releases energy to start the train again when it leaves? The former is hard to imagine, the latter seems like it involves many inefficiencies but it might still be worth it.

Re:Isn't this an old idea? (3, Informative)

wagnerrp (1305589) | more than 2 years ago | (#37300596)

They're talking about the latter. Subway systems run an electrified third rail, charged with somewhere between 500-1500VDC. Trains draw power off this rail as needed, and power substations are located periodically throughout the system to supply it with power. They're talking about using the traction motors to stop, instead of brakes, and pumping that power back into the DC rail. Then setting up flywheels attached to the power substations that intelligently buffer the power supplied to the rail.

When the train brakes and dumps power onto the rail, the flywheel sucks it up. When the train wants to take off again, it is powered by the stored energy in the flywheel. Due to the low rolling resistance of metal wheels, trains require surprisingly little power to operate. Between the energy capture efficiency, and low operating needs, such a subway would run on only a small fraction of its current draw.

Re:Isn't this an old idea? (0)

Anonymous Coward | more than 2 years ago | (#37300720)

The reason they don't do this is that it would require an insanely large inverter and insane amounts of current through the third rails.

Re:Isn't this an old idea? (2)

Technician (215283) | more than 2 years ago | (#37300628)

This may be simply a way to store energy on a line with few cars on it. Most power supplies are rectifies and are unable to put excess power back into the grid for storage. Excess regen power must be consumed by another train or dissapated as heat in braking load resistors. I think what they are trying to do is use the flywheel so voltage rise due to excess regenerative braking is captured in the flywheel in the powerhouse.

Most trains do not have this. They rely on braking resistors for excess regenerative braking. Elevators have this same issue in locations that prohibit regenerative breaking putting power back into the grid.

Re:Isn't this an old idea? (1)

Warwick Allison (209388) | more than 2 years ago | (#37300724)

It means the person writing the article is an imbecile. All electric trains already brake by shunting power out to the grid, they suggest keeping it local to a station in a flywheel. Very little net gain really, just a bit of peak power smoothing. Better to have utility-scale power storage in the grid, for smoothing everything, not just trains. Flywheels is just one (tried and true) system for doing that.

Re:Isn't this an old idea? (1)

nzac (1822298) | more than 2 years ago | (#37300226)

The idea might be old but getting it working on a much larger scale is not trivial. Being able to store 100 or so megajoules is pretty cool also.

Re:Isn't this an old idea? (1)

Anonymous Coward | more than 2 years ago | (#37300228)

Yes, it's an old idea in general. But trains, despite being full-electric or diesel-electric-hybrids for decades, have traditionally just thrown out their braking energy as heat, either kinetic->electric->resistor bank or kinetic->friction brakes. So it's not new technology, it's just moving existing technology into a slow-moving, capital-intensive industry.

Toyota called... (-1, Troll)

RobinEggs (1453925) | more than 2 years ago | (#37300204)

...and they want their invention back. It's the same principle behind the battery charging a Prius does when it brakes.

I'm not trying to piss all over this with standard slashdot armchair-technologist elitism; it's wonderful that someone is implementing the "long-standing need" (as it would be called in a patent application) for this obvious but unexploited idea. I'm just pointing out that flywheel gizmos in transportation are a *very* old idea, and there's no need for anyone to get psyched up as if this is a revolutionary invention.

Re:Toyota called... (4, Insightful)

artor3 (1344997) | more than 2 years ago | (#37300254)

I'm gonna go out on a limb here and say there's a lot more energy involved in moving subway trains than your typical Prius. Perhaps the trick here is creating a system able to store so much energy efficiently?

We've had airplanes since the Wright brothers in 1903, and jetliners since the early 50s. That doesn't mean that Boeing's 787 is an old idea and not worth talking about. The real advances in engineering are always in the little fiddly bits that screw you over when you first try to scale up.

Re:Toyota called... (0)

Anonymous Coward | more than 2 years ago | (#37300374)

Hmm... it seems like they want to use flywheels to store the energy on that overly green page. IMHO, it seems far easier to just synchronize the trains so one is accelerating while another is decelerating. That's still a complex problem, but it requires far less hardware. Of course, it's a flywheel company. When all you have is a hammer, everything looks like a nail. Doubly so if you make money by hammering.

Re:Toyota called... (1)

zippthorne (748122) | more than 2 years ago | (#37300740)

I think it might be less complex than you imagine. Instead of trying to manage the entire system like a big dance that has to be carefully coordinated, you just build in some slack and treat each station like a newton's cradle: just hold the departing train until the arriving train.. arrives.

You do have to build in enough slack to make sure that the doors are all shut, and of course there needs to be a plan to deal with the possibility that a train cannot clear the station in time for the arriving train, and you won't be able to do a constant acceleration on either side. 1G deceleration of the arriving train at the beginning of its decel corresponds to a lot more than 1G of acceleration for the departing train....

Re:Toyota called... (1)

amiga3D (567632) | more than 2 years ago | (#37300392)

Almost all technology improvements today are just refinements or new uses of old tech. Look at what we do with nuclear power. We boiled water for steam with coal. Now we boil water with nuclear for steam. We only look tall because we're standing on the shoulders of giants.

Re:Toyota called... (0)

Anonymous Coward | more than 2 years ago | (#37300436)

All technology improvements EVER are just refinements or new uses of old tech.

Fixed.

If you go far back enough, you'll find that every form of technology grew out of imitating/advancing things that already existed.

I salute you Cavemen Ugg and your using rocks to break open nuts. It's thanks to you that we can now split atoms.

Re:Toyota called... (1)

bertok (226922) | more than 2 years ago | (#37300526)

A lot of engineering is refinement, yes, but scientific advancements are often revolutionary.

Electricity for example had no equivalent before it -- it was an entirely new concept. One could argue that the internal combustion engine is just a variant of a piston steam engine, but the steam engine itself was a new concept: converting thermal energy to work by allowing hot gases to expand against a piston in a reciprocal way. That was so revolutionary that it started the Industrial Revolution!

Re:Toyota called... (2)

rthille (8526) | more than 2 years ago | (#37300662)

It could be argued that the water wheel started the industrial revolution...

Re:Toyota called... (0)

Anonymous Coward | more than 2 years ago | (#37300746)

If something is an entirely new concept it would be impossible to understand since we would have no basis to understand it WITH. At least some element of the past MUST be used to evolve or discover said concept.

Everything comes from everything else. Since all things are based on their *relation* to other things, NO invention or concept can be considered wholly new or unconnected from the past.

Toyota called AGAIN (2)

ChrisCampbell47 (181542) | more than 2 years ago | (#37300360)

... to let you know that you're playing fast and loose with differing types of braking systems. Flywheel-based KERS, electric motor+battery regen braking, different things that are the same "in principle" only if your principle is "slow down with some mechanism besides direct generation of heat".

Further, nobody is bothering to read the article, is just taking the summary here at face value. But that's par for the course here. Nevermind.

Re:Toyota called... (-1, Offtopic)

RobinEggs (1453925) | more than 2 years ago | (#37300370)

Ok, I honestly want an explanation as to why my original post was "trolling".

Seriously, I'm all ears. Damn near everything I post gets modded troll by *someone*, and I'm seriously starting to wonder if I have a personal stalker.

It's only trolling or flaming if someone said it *exclusively* to piss people off. Just saying something you disagree with, or something controversial, or something dead wrong, or something just plain crazy is *NEVER EVER TROLLING*.

Now get that through your heads before you spend any more mod points.

Re:Toyota called... (1)

wagnerrp (1305589) | more than 2 years ago | (#37300630)

Because the concept of regenerative braking has been around long before the Prius was a twinkle in Toyota's eye. Bringing them into this, alluding that they invented it, is what makes you sound like a troll.

Re:Toyota called... (0)

The Dawn Of Time (2115350) | more than 2 years ago | (#37300698)

Lighten up, Francis.

Re:Toyota called... (1)

amiga3D (567632) | more than 2 years ago | (#37300378)

I know this principle was used a couple of decades before the prius by some university that was building an experimental 100+ mpg auto. Don't know who patented it or even if it is patented. It might even be a lot older than that.

Re:Toyota called... (1)

bromoseltzer (23292) | more than 2 years ago | (#37300398)

It's not a revolutionary invention, but it should be very helpful if they can cut the peak and the average power draw on the power grid by a substantial amount. There's an energy cost saving and also transmission grid saving. You don't need such a heavy connection between the train system to the general power grid.

hm (1)

Osgeld (1900440) | more than 2 years ago | (#37300236)

never really thought about how much juice a subway train draws on startup. thanks

Regenerative braking? (2)

hawguy (1600213) | more than 2 years ago | (#37300250)

How is this different from traditional regenerative braking (they even mention regenerative braking in the article) that's already in wide use by electrified transit providers? I don't see how feeding energy into local flywheels is any different than feeding it back into the grid? Surely a grid that's capable of delivering megawatts of power for to start a train is capable of absorbing (fewer) megawatts of power for braking?

Is the 30 seconds @ 3 - 4MW figure mentioned in the article accurate? That's a 6000 amp draw for a 600V system, sounds like a lot of current over a relatively small conductor -- the conductors that I've seen appear to be around a 4/0 gauge, which is only rated for around 250A. Granted, for only 30 seconds it could exceed this rating, but 6000A?

Re:Regenerative braking? (1)

kevinqtipreedy (450228) | more than 2 years ago | (#37300300)

I was thinking the same thing. I'm guess what they meant to say was 3-4 Megawatt Hours over the 30 seconds, which would bring and amperage to 42-56A.

Re:Regenerative braking? (3, Informative)

tftp (111690) | more than 2 years ago | (#37300302)

The kinetic energy of 100 [short] tons moving at 80 mph would be 58 MJ [wolframalpha.com] . The energy of 4 MW during 30 seconds will be 90 MJ [wolframalpha.com] . So the numbers appear to be correct, plus or minus my guesses on the weight and speed and everything else.

Re:Regenerative braking? (3, Interesting)

Nemyst (1383049) | more than 2 years ago | (#37300348)

I've done some digging and it'd appear that the figure is actually correct. This thread [nyctransitforums.com] about the NYC subway system seems to say that the trains actually draw at maximum 10,000 amps, or 6 MW at 600 V. The 3-4MW figure would then be a good estimate.

I'm going to guess that feeding the energy in flywheels causes less power loss than going back and forth the lines, though it may very well be that they just want to keep the city dependent on their flywheels to use the regenerative breaking system they'd implement.

Re:Regenerative braking? (3, Informative)

Dunbal (464142) | more than 2 years ago | (#37300758)

Electric motors draw maximum amps at the very beginning just before they start turning. After that the draw is significantly less because resistance increases. You know, V=IR rewritten as I = V/R. The voltage is fixed, the resistance is close to zero when the motor is not turning so the amps go sky high. But only for an instant. As soon as the motor starts turning resistance picks up due to electromagnetic effects and the current draw falls. This is why you'll burn out a motor switching it on and off too quickly. You're shooting tremendous amounts of current through a non-turning motor. All that huge amount of current heats up the coils until something melts. However the 10,000 amp figure is peak, not continuous for 30 seconds. Therefore it's not fair to use that figure for calculations over a 30 second acceleration period. The amps drawn would form a curve, and for that you'd need something a little more complex than y = mx+c to figure it out, ie knowing the exact curve for those engine types/trains and some calculus.

Re:Regenerative braking? (0)

Anonymous Coward | more than 2 years ago | (#37300462)

I don't see how feeding energy into local flywheels is any different than feeding it back into the grid?

The difference is, if they feed the energy back into the grid, then Vycon doesn't sell as many flywheels.

Re:Regenerative braking? (2)

robbak (775424) | more than 2 years ago | (#37300506)

two points: Overhead systems like you see normally use much higher voltages than 600V, for the reasons that you quote. Third-rail systems can deal with much higher currents.
Secondly, A system that can deliver that current could only absorb it if it has somewhere else to send it - another accelerating train. Another poster suggested that, most of the time, the energy in the braking currents are, at least partially, lost in the resistances of the third rail, carrying it miles until it finds an accelerating train to use it. Absorbing it in a local storage flywheel and pumping it back a few minutes latter makes good sense.

Re:Regenerative braking? (1)

timeOday (582209) | more than 2 years ago | (#37300640)

Has anybody tried just building the stations on hills? (I.e. putting the platforms at less depth than the rest of the tunnel?) Then the trains are slowed coasting uphill into the station, and pick up speed going downhill out of the station.

I guess you could even have the trains pull onto a teeter-totter tilted up as they arrive and down as they leave, by a piston, so they wouldn't have to go a train length on level ground before being accelerated by the downhill.

Re:Regenerative braking? (2)

DaleSwanson (910098) | more than 2 years ago | (#37300754)

Has anybody tried just building the stations on hills?

http://en.wikipedia.org/wiki/Victoria_line [wikipedia.org]

The line has hump-backed stations which allow trains to store gravitational potential energy as they slow down and release it when they leave a station. This provides an energy saving of 5% and makes the trains run 9% faster.

I suppose it may be hard to retrofit the hills. Although, wiki calls it a slight hill. If it were only a few feet then I would think it would be worth it.

Some quick math shows that an object at 40 mph (18 m/s) has about the same energy as it would gain from a 16 meter fall. That's certainly doable, but probably too much for a retrofit, as it would require new tunnels. Then again, any hill would help a little.

Re:Regenerative braking? (0)

Dunbal (464142) | more than 2 years ago | (#37300762)

Has anybody tried just building the stations on hills?

Yah lots of hills in downtown Manhattan. You could just knock some of those buildings down land is cheap over there I hear. Didn't they like buy the whole island for $24 or something? Or you could dig the tunnels a little deeper because it's just dirt, right? And there's no ground-water from the Hudson river to worry about when you blast your way deep enough....

Re:Regenerative braking? (1)

ryanov (193048) | more than 2 years ago | (#37300854)

Clearly you don't realize that this was done on some lines in Manhattan. Do you even live anywhere near there to make such a snarky post on the subject?

Re:Regenerative braking? (5, Informative)

Anonymous Coward | more than 2 years ago | (#37300594)

6000 amps at 625 volts is EXACTLY what a subway train draws when it starts. I should know, I work for the Power department of the New York City Subway system.

Re:Regenerative braking? (1)

sam0737 (648914) | more than 2 years ago | (#37300652)

6000A maybe a bit stretch, but it's not out of the ball park.
It takes 1500A@750V to accelerate a 6-car train in Beijing.

Scale to 10-car and 600V, you get 3000A.

Energy != work (2, Insightful)

zill (1690130) | more than 2 years ago | (#37300272)

a 10-car subway train in New York's system requires a jolt of three to four megawatts of power for 30 seconds to get up to cruising speed — that's enough energy to power 1,300 average U.S. homes."

For how long?

Re:Energy != work (1)

webdog314 (960286) | more than 2 years ago | (#37300314)

The way I read it, 30 seconds.

Re:Energy != work (2)

bromoseltzer (23292) | more than 2 years ago | (#37300344)

a 10-car subway train in New York's system requires a jolt of three to four megawatts of power for 30 seconds to get up to cruising speed — that's enough energy to power 1,300 average U.S. homes."

For how long?

For 30 seconds, more or less, if a home is ~ 2-3 kW.

Re:Energy != work (1)

Anonymous Coward | more than 2 years ago | (#37300364)

That's not the point. The train, while accelerating, consumes 3-4MW of power, placing 3-4MW worth of strain on the grid's energy budget, which is being equivocated to the load of 1300 average homes. The grid is rated for peak instantaneous power, not work.

If subway trains use regenerative braking to feed power back to the grid during periods of high demand they are reducing the strain on the grid, lowering demands on peaker generating stations.

3MW 1300 average homes 4MW

so

2.3kW 1 average home 3.1kW

The numbers themselves seem reasonable.

Re:Energy != work (1)

Idarubicin (579475) | more than 2 years ago | (#37300510)

If subway trains use regenerative braking to feed power back to the grid during periods of high demand they are reducing the strain on the grid, lowering demands on peaker generating stations.

No, no, no. If the trains were feeding the braking power back into the grid, it would make the situation worse, not better. Every time a train stopped there would be fifteen seconds of reduced load (by four megawatts or so) during braking, followed fifteen seconds of passenger boarding, followed by thirty seconds of increased load (by three or four megawatts) during acceleration out of the station. Instead of having a swing of four megawatts of grid load, there would be local swings of eight megawatts per train. Not good.

The advantage here is that the energy is stored (in flywheels at each station) and fed back to the same train a little bit later. Nothing goes back to the grid, and a lot less is drawn from it. That's how this (or other, similar systems which have been proposed in the past) would reduce the strain on the grid.

Re:Energy != work (1)

Dunbal (464142) | more than 2 years ago | (#37300794)

IANAElectrician, but if you're storing the power locally couldn't you isolate sections of the track from each other and the grid in general and have an "acceleration" track to avoid what you describe? The connection with the rest of the rail could be broken when a train is about to leave, and the flywheel + grid is fed into a predetermined length of isolated track. The train accelerates with power from the flywheel (plus some grid) and crosses onto the main track via inertia but since it's at speed already the current draw is not that much so there shouldn't be a huge change when the train switches to the main track. Likewise the decelerating train leaves the main track and pumps energy back into the flywheel system only, not the whole network.

2-3kW per home is reasonable? (1)

dj245 (732906) | more than 2 years ago | (#37300602)

My energy use last month was about 22kW-hr per day according to the utility. That's about 920 watts continuously. This is for a 3 bedroom house inhabited by 2 people, with a 55" TV, a couple computers, air conditioning set at 77F with an average outside temperature of 75F to 90F.

Our house is pretty energy efficient, and our energy use is typically below the norm. I do work in the power industry, and the average that they tend to use is 1.2kW. Not 2 or 3kW average. This is the problem when journalists abuse measurements like this.

Re:2-3kW per home is reasonable? (0)

Anonymous Coward | more than 2 years ago | (#37300844)

22 fucking kw/day? do you drive all-electric cars? are you growing pot man?

Re:Energy != work (1)

knuthin (2255242) | more than 2 years ago | (#37300400)

As humans made conscious about every little energy we waste by TV and internet and other stuff, we are so desperate to find new sources of energy.

After extracting energy unsuccessfully from cow fart, cow dung and human pee, now we do this. :/

Slashvertisement? Overthinking? (0)

Anonymous Coward | more than 2 years ago | (#37300280)

10-car subway train in New York's system requires a jolt of three to four megawatts of power for 30 seconds to get up to cruising speed â" that's enough energy to power 1,300 average U.S. homes.

1. Misleading at best. That's "power 1,300 average US homes for 30 seconds".

2. So why not have subway cars stagger start on as many lines as possible? You know, to limit concurrent start of trains. This should limit any "peak power emergencies".

3. Don't train systems have a separate, dedicated power lines with their own transformers and such, effectively limiting the amount of power they can draw from grid at once? This basically "browns out" the subway train system, unaffectedly the larger grid.

4. Seems like slashvertisement.

U-shaped tunnels (1)

Anonymous Coward | more than 2 years ago | (#37300296)

I read somewhere that subway tunnels dip down between stations, so that the train gets an automatic boost as it departs and breaking assistance as it arrives at the next station. In physics terms, there is a transfer between kinetic energy and gravitational potential energy. It sounds like an elegant low-tech solution, -- no need for flywheels, and nearly as fun as a rollercoaster.

Re:U-shaped tunnels (1)

ChrisMaple (607946) | more than 2 years ago | (#37300530)

I've ridden the NYC subways and seen the tracks. If the stations are high points of any significance, I haven't seen it. It seems like a nice idea, but there is one significant problem. Steel (wheels) on steel (tracks) has a low coefficient of friction, particularly if there's water or oil involved. It's not uncommon for a subway train to wait just outside of a station, waiting for the track to clear. It would then have to start up and climb the grade into the station. To do this, the grade probably shouldn't exceed about 3%. (Although that's a limit for railroads. Subways are powered at each car, so they can tolerate steeper grades.)

To get back to the article, a flywheel seems like a poor idea, unnecessarily complicated and dangerous. If there's energy storage involved, then store it by lifting a weight 50 feet or so.

Re:U-shaped tunnels (1)

ryanov (193048) | more than 2 years ago | (#37300862)

Only some of the lines in NYC do this, and in some parts, but they definitely do exist. I can't recall which, but I looked into it the first time I heard of the idea.

Better idea (4, Funny)

SuperKendall (25149) | more than 2 years ago | (#37300330)

Forget this fancy regenerative braking nonsense.

What better way to get one train totally stopped, while startup up another? The solution to this problem is obvious, simply let an incoming train hit a parked one. The kinetic energy will be transferred, the parked train will be in motion while the formerly moving train is almost totally stopped.

All you need to make it work is some very good bumpers and perhaps strengthening the hand-straps.

Re:Better idea (1)

amiga3D (567632) | more than 2 years ago | (#37300402)

Careful there, somebody might not realize you're joking.

Re:Better idea (5, Funny)

SuperKendall (25149) | more than 2 years ago | (#37300608)

Well I did hope the bit about handstraps was enough of a clue...

But come to think of it, the brilliance of the plan is how it keeps the trains on an exact schedule. Why yes, the train IS leaving at 10:43 even if you try to hold the door.

Re:Better idea (3, Funny)

formfeed (703859) | more than 2 years ago | (#37300410)

What better way to get one train totally stopped, while startup up another? The solution to this problem is obvious, simply let an incoming train hit a parked one. [...] All you need to make it work is some very good bumpers and perhaps strengthening the hand-straps.

I'd add a pair of gigantic springs.

Re:Better idea (2)

Ryanrule (1657199) | more than 2 years ago | (#37300484)

Well, you could use the energy of the train stopping on one side to fire off the train on the other side.

Re:Better idea (1)

Dunbal (464142) | more than 2 years ago | (#37300814)

Or have the passengers push the trains to the next station.

Re:Better idea (0)

Anonymous Coward | more than 2 years ago | (#37300600)

Or better yet, don't stop the trains. Just like at Disney World, but much, much faster!

Re:Better idea (1)

zippthorne (748122) | more than 2 years ago | (#37300658)

That only works if you've got perfectly inelastic trains.....

Re:Better idea (1)

Tablizer (95088) | more than 2 years ago | (#37300824)

Flintstones lives!

Re:Better idea (0)

Anonymous Coward | more than 2 years ago | (#37300888)

This is an amusing idea if it wasn't for the whiplash and lawsuits it would induce.

They probably should have just put flywheels in the lead and tail car to give the subway a boost starting up.

I wonder if any of this applies to the LIM's used in the Bombardier ART technology. They pretty much stop and start on a dime if needed.

already happening? (-1)

Anonymous Coward | more than 2 years ago | (#37300336)

Surely the other trains in the network are already working as "flywheels", so what advantage do additional flywheels offer?
Maybe the line is configured with many separate sections. In which case local flywheels in each station would definitely help.

That is assuming that the trains already have regenerative braking. If they don't, then none of the article makes much sense.

Is it practical? (0)

Anonymous Coward | more than 2 years ago | (#37300338)

Is it practical to have the passengers push start the subway trains?

Sounds Interesting (1)

Anonymous Coward | more than 2 years ago | (#37300412)

So the basic idea is to have a giant flywheel in the train station that is spun up from the incoming train's electric regenerative braking. It sounds ingenious because it doesn't require any fancy equipment, just voltage regulators and some fancy switches. Plus any light rail line could be retrofitted.

90% efficient sounds pretty optimistic, I'd think 60-70% is more realistic without seeing a real-world proof of concept. Still, 60% of four megawatts is a freaking huge amount of power.

Re:Sounds Interesting (2)

j-beda (85386) | more than 2 years ago | (#37300534)

Surely they could just feed the generated electricity back into the grid without all the local flywheels being necessary? As I recall, the Vancouver trolley buses have been doing this type of thing since at least the 1970s. If the grid can handle the output necessary to accelerate the trains, surely it could handle the input of slowing them down?

Your energy calcs are off (-1)

Anonymous Coward | more than 2 years ago | (#37300438)

Your energy calcs are off. 3 or 4 megawatts for 30 seconds = ballpark 3000 kilowatt-hours. Typical US household electricity consumption is around 9,000 kWh per year. Each stop is good for 1/3 of a house. Of course, each train stops many times a day, and there are lots of trains, so lots of stops = potential power for lots of households. But 1,300 for one stop is a bit of an stretch.

That's 1,300 houses for 30 seconds. (1)

robbak (775424) | more than 2 years ago | (#37300558)

During the startup, the train uses as much power as 1,300 houses. (Does anyone else think that "houses" is a silly unit of power?)
So, the energy required to accelerate a train (it takes 30 seconds) could power 1,300 houses for 30 seconds.

Re:That's 1,300 houses for 30 seconds. (1)

Dunbal (464142) | more than 2 years ago | (#37300822)

Yes especially in Manhattan, it should be 1300 one bedroom studio apartments.

better to use ultra-caps at the station (2)

WindBourne (631190) | more than 2 years ago | (#37300504)

By using ultra-caps at the station, they get to drop the price of these. In doing so, they make it available for other technology. The advantage of ultra-caps is that it has power. In addition, while some of the ultra-caps do not retain energy for days without loss, this is simply shot back into the system in under 5 minutes. The loss is nominal. Finally, most rail systems have more cars, trains, then stations. It is actually cheaper to put these at the stations, using the electric system, then to retrofit all of the cars. Also, not making the cars carry the charge system around is more efficient.

Try it with airplanes (3)

crow (16139) | more than 2 years ago | (#37300518)

The energy in subway trains is dwarfed by the energy used and lost on runways for jetliners. Imagine a system where, when a plane touches down, the energy is absorbed by a ground-based system that is then used to assist in takeoff for the next plane.

I suppose the natural first use of this would be on aircraft carriers. They already use systems to assist the takeoff, and they use hooks and cables in landing. They just need to efficiently store all that energy for reuse. (Then, again, when you have your own private nuclear reactor, energy for the catapult system may not be such a big deal.)

Re:Try it with airplanes (3, Funny)

BradleyUffner (103496) | more than 2 years ago | (#37300612)

The energy in subway trains is dwarfed by the energy used and lost on runways for jetliners. Imagine a system where, when a plane touches down, the energy is absorbed by a ground-based system that is then used to assist in takeoff for the next plane.

I suppose the natural first use of this would be on aircraft carriers. They already use systems to assist the takeoff, and they use hooks and cables in landing. They just need to efficiently store all that energy for reuse. (Then, again, when you have your own private nuclear reactor, energy for the catapult system may not be such a big deal.)

Nuclear Powered Subway Trains? I LIKE it!

Re:Try it with airplanes (0)

Anonymous Coward | more than 2 years ago | (#37300660)

I believe Carriers already do something fairly efficient - US Nuclear ones at least use compressed steam generated by their reactors to shoot the slingshot that is used to assist take-off.

Re:Try it with airplanes (2)

Baloroth (2370816) | more than 2 years ago | (#37300672)

No, that wouldn't really work. Most of the energy to propel a plane is used up by wind resistance (deliberately). The plane needs to actually force the air downwards with the wings to fly, so no matter how low a drag the rest of the system has most of the energy isn't going to be retained. Most jumbojets run at pretty close to max power for the whole flight, because they need to due to energy loss. A subway, on the other hand, runs through mostly inertia (similar to how most cars work.) Most of the energy is used getting up to speed, very little staying there and most of this can be recouped. This is also why hybrid cars are more fuel efficient than regular vehicles. Their theoretical highway mileage would in fact be the same if non-hybrids didn't need such a large engine for acceleration.

Not to say your idea is terrible, it just wouldn't have much impact. Also, storing energy from a plane would be technically extremely difficult, although the US Navy's new electromagnetic launch system might be able to do it.

Re:Try it with airplanes (0)

Anonymous Coward | more than 2 years ago | (#37300778)

the navy has no need for such a technology. Ever since the USS Enterprise, carriers have had an abundance of power and not much to do with it.

Complicating the landing hook is a stupid idea.

Re:Try it with airplanes (1)

Dunbal (464142) | more than 2 years ago | (#37300846)

So would pilots be encouraged to make really really really hard landings in order to create more energy for the departing aircraft? And who would clean up the mess?

Re:Try it with airplanes (0)

Anonymous Coward | more than 2 years ago | (#37300874)

Sorry, won't work with aircraft. The amount of energy available in a landing plane is a tiny, teeny fraction of the energy consumed during the trip. Most aircraft bun energy to get to altitude, then set for a "most economical" rate of fuel burn for cruise, and then more or less coast into the airport once they get reasonably close.

It takes me about 10 minutes to climb to 5,000 feet in my Cessna 182. When I descend, I also do so at around 500 feet/minute, and I don't use flaps or anything to induce drag until I'm down near the airport, at least in the pattern if not on final. By the time I get anywhere near the ground, all the energy I spent climbing has been spent.

Subway != Energy Efficiency vs Automobile! (0)

Anonymous Coward | more than 2 years ago | (#37300618)

So a 10 car train requires 30 MW for 10 sec to accel to cruise speed. That's 300 M Joules.

A car consumes about 100 kW during accel. For 10 sec of accel time, a car consumes 1 M Joule.

It would seem to me a 10 car train better have 300 people on it before it starts consuming less energy/passenger during a given accel time. I doubt this happens except in the extremes of rush hour. 30 people/car in every car of a 10 car train is believable during a rush hour. But the energy savings are much less than I'd of thought. Include the fact, that the train must travel with or without passengers, at all hours, and I'm really starting to lose faith in the proposition that mass transit is more energy efficient let alone much more fuel efficient than personal automobile transport.

At least a subway can be powered by coal or nuclear power and not oil/petrol.

Humm......

Re:Subway != Energy Efficiency vs Automobile! (1)

The Dawn Of Time (2115350) | more than 2 years ago | (#37300742)

30 people per car in the peak of rush hour? I guess you don't ride a lot of subways.

Power != Energy (4, Insightful)

FrankDrebin (238464) | more than 2 years ago | (#37300650)

requires a jolt of three to four megawatts of power for 30 seconds to get up to cruising speed — that's enough energy to power 1,300 average U.S. homes.

The corrected sentence is much less impressive: "— that's enough energy to power 1,300 average U.S. homes for 30 seconds."

"Subsidize" city power systems? (1)

Radical Moderate (563286) | more than 2 years ago | (#37300686)

Don't they mean supplement? I realize it's Saturday, but come on, editors.

If we could only power our subway with stupidity (1)

harrytuttle777 (1720146) | more than 2 years ago | (#37300764)

we would have the subway energy crisis solved. Or better yet if we could only figure out a way to harness the power of slashdot faggotry to displace electrons,we could solve the world's energy problems.

Does your Mom know that you are a faggot?
-Richard simmons.

Regenarative braking? (2)

Hamsterdan (815291) | more than 2 years ago | (#37300914)

Like the Prius, the Lexus Hybrids, the Ford Escape, and many of the hybrid cars on the market?

Montreal's Societe de Transport de Montreal is testing hybrid buses (perfect use for a hybrid vehicule)...

I can see Delivery vehicules (Purolator, UPS, DHL, FEDEX, restaurant delivery) using that, they are always stop and go, so regenerative braking makes lots of sense.

If you're only doing highways, a hybrid won't do much, except use more gas for the added battery weight...

The key is synchronization (2)

realyendor (32515) | more than 2 years ago | (#37300940)

If you can synchronize arrivals with departures at the same (or a nearby) station, energy regenerated through braking can be immediately used to power the acceleration of another train. If it is not synchronized, the power is wasted (unless they have batteries or some other power cache, which would surely introduce its own inefficiencies).

I once heard a story (though unfortunately I have no references--it may very well be an urban legend) that the Vancouver SkyTrain continued operating through a power outage thanks to (a) its very efficient linear induction motor propulsion & braking, (b) operating at a reduced speed (to minimize the impact of wind resistance), (c) supplementary power from backup generators, and (d) synchronized arrivals and departures from stations in conjunction with regenerative braking. The synchronization could be done precisely and programatically because it is a fully-automated system.

Load More Comments
Slashdot Login

Need an Account?

Forgot your password?
or Connect with...

Don't worry, we never post anything without your permission.

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>