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How much power is generated by dynamic braking?
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Correct me if i'm wrong, but slugs are ususally the victims of "ballasting" as a way to replace the mass of the prime mover, generator and associated systems. So, in places where slugs are used to put power-on-rail for hill climbs, mass is a good thing and the entire fuel tank volume is available for use. In that scenario, a battery storage system makes a lot of sense. Back of the envelope (15lbs/ gallon, incl. cables, blowers, etc.), a fuel tank would hold about 1/2 the batteriessomeone (forget who) cites above. Using his energy numbers, and applying the electric-car rule-of-thumb 80% total system efficiency, that's a little more than 500HP-hours put on the rail, or about 45 gallons of diesel fuel (at 0.5lb/HP-hr) that could be re-used per slug, per charge cycle. If you don't deep-deep-cycle the cells too often, you could get something like 2000+ cycles out of a good set of vibration-resistant batteries. <br /> Figuring a 50% depth-of discharge limit, that's about $45k in fuel savings alone, (California prices to the tourist line I sometimes wrench for) which about pays for the batteries and labor to swap them. (lead-acid recycles, so disposal is essentially free) <br /> I'll let someone else speak to the maintenance requirements of locomotive electricals, but batteries are pretty simple beasts; as long as you don't let them get too hot or too cold and add water every week or or so, they're fine. <br /> <br />The biggest wrinkle I can see is that you can safely draw a higher energy rate out of lead-acid than you can put back in. Some sort of electrolyte cooling could help, but any engineered cooling you add to the battery system hurts cost and reliability. <br /> <br />which brings us to: <br /> <br />Flywheels can be designed for much better charge and discharge rate curves and aren't inherently cycle-life-limited like batteries. They do better on a mass-energy density basis, but really lose out on volume-energy density. <br />They DO add another wrinkle, in that highly stressed rotors don't like vibration; it tends to eat delicate bearings and crack things; and cracked flywheels tend to come apart violently. (the tip speeds of high-density flywheels are near that of a rifle bullet, and the tips is where the majority of the energy is stored.) Vibration can be engineered around, however, and orientation, containment and distance are good mitigating factors against rotor burst events. (Plus, show me the rifle that can shoot lengthwise though a 16-645 and generator, and I'll be your slave for a week <G>) <br />Net result, you could leave the full-size hood on a slug, and get probably twice the benefit from a 'flywheel slug' as you could from a 'battery slug.' <br /> <br />Using either technology, that's effectively 500+ fuel-, maintnenance- and emission-free horsepower made out of what is basically a used-up locomotive; you'd have to balance the conversion cost against what you'd get on the used locomotive market and the utility of having that 500 HP available as continuous duty. That again could be engineered around by adding an autostart OTR truck powerplant, and add that much more "surge" power to your 'powered slug' for a slight increase in cost, complexity and volume. <br /> <br />In summary: It's not a silver bullet, by any means, but a 'storage slug' arrangement could be a net money saver to a railroad with a few short, steep hills, or lots of slippery ones. I wonder how long it'll take RailPower to iron out the wrinkles? (I hear they are working on it.) <br /> <br /> <br />(someone asked about Supercaps- Great discharge and charge rates, lousy energy density. Watch the technology though, there's lots of room for innovation yet.) <br />
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