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Comment Re:DC is more dangerous (Score 1) 357

DC is harder to turn off safely. A high current contactor will arc under both AC and DC - but an AC arc tends to be self extinguishing. Solid state switching is less efficient and requires power to activate. They also tend to go up in flames when they fail.

HVDC is used only for long distance transmission, where the capacitive load for AC systems becomes a major source of loss. The only other time it makes sense is when the current required is so high, the skin effect at AC frequencies results in cables that need to be substantially larger. In cases like that, though, it's often easier to go with multiple smaller cables anyway.

AC is demonstrably easier to engineer around, and safer as a whole. There are some good arguments to be made that DC might be safer under some circumstances should you become part of the circuit - but the whole idea is that people should not become part of the circuit in the first place, so that's a non-issue.

Also, regulating DC to various voltages just means it converts it to AC first then back to DC... unless you're using linear regulators in which case the unneeded power is dumped as heat!
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Comment Re:Why? (Score 1) 451

Citation needed.

You seem to be suggesting that containers are unpacked at the dockyards. That's absolutely absurd for legal and liability reasons. The only people who are going to open up a container at the port are going to be the customs agents.

Intermodal containers are placed directly onto road trailers and train cars for transport. Repacking of goods into branded freight happens once the goods arrive at that distributor's warehouse facilities. From there the items will be unpacked and repacked as necessary to get the items where they're going.

If a shipping container has items for more than one destination, then they will only be unpacked at the logistics company's facilities. If you don't fill a container you're paying for a full container anyway because nobody but you or an authorized handler (consolidator) will mix your cargo with someone else's. That means a shipping container as a whole always has exactly one destination.
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Comment Re:Why? (Score 1) 451

How well maintained is the rail network in the USA? Can it actually handle this kind of traffic?

It already does. What do you think happens to the vast majority of cargo containers that arrive in maritime ports? A short journey by truck to the rail yard and off into the heartland.

It's not high speed rail, of course - mostly for safety. But by the time you're into the intra-continental rail network you've already gotten your benefit out of the project.
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Comment Re:Why? (Score 1) 451

My car can do 100MPH but rarely does.

Having a top speed of 25 knots is not the same as actually traveling at 25 knots. The trend over the past few years, especially, has been to slow down to reduce fuel consumption and save money.

And all that assumes ideal sailing conditions.
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Comment Re:Why? (Score 3, Interesting) 451

I had the same question, honestly. But it might have some benefits...

A cargo ship has a top speed of under 25MPH (20 knots). A Class 5 freight train can hit 80 MPH and there's no *technical* reason why they couldn't go even faster. Even with the increase in distance by taking the long way around, you can maybe reduce transit time. Such trains could also load and unload deep inland, closer to where the cargo is needed, eliminating multiple handling steps.

I still don't think it's a *good* idea, but it's slightly less crazy than it might initially sound.
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Comment Re:Why not both? (Score 1) 239

Offer void where constant-speed is not the most efficient. Pumps and fans that can match the actual demand by varying speed will be more efficient than running a full out and bypassing or artificially increasing head pressure to get the desired flow.

You're also not going to put an across-the-line starter on a motor larger than about 50HP unless you like replacing equipment. You'll always have a soft starter to get things going - this is doubly important if you're starting the motor under load.
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Comment Re:Why not both? (Score 1) 239

So called Brushless DC motors are actually permanent magnet rotor, synchronous AC motors?

They are virtually identical, yes. There might be some nuanced differences in their physical construction or drive (sinusoidal vs trapezoidal waveform, for example) but the operational principle is the same.

For fractional horsepower motors there's no cost-benefit to doing sophisticated controls in most cases. You just need it to turn on and off at one, sometimes two or three speeds and the load is more or less constant. I wouldn't expect that to change any time soon.
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Comment Re:Efficiency (Score 1) 889

Flywheels can be charged up lots faster than batteries.

That depends entirely on the design of the flywheel/battery. But you know what flywheels do better than batteries? Leak. An idle flywheel will lose energy much faster than an idle battery.

Supercapacitors are neat but have the worst volumetric energy efficiency of then all.
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Comment Re:Efficiency (Score 1) 889

But for the cost and weight, a battery is better than a flywheel in essentially every aspect. For however much you reduce the required size of a flywheel, you can reduce the battery size as well.

Battery systems are damn close to 100% efficient if you're not too close to fully charged or fully discharged, or not diving the current much higher than 1.0C.

There is no advantage to using a flywheel at all. None.
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Comment Re:Easy Conclusion If Perceived Costs & Range (Score 1) 889

In 2013, the average price for a new car was $32K. Many EVs available right now are below that even *before* any state or federal incentives, and many more hit that point after incentives.

Meanwhile, the average price for a used car was $16.8K. I don't know where you'd get a sub-$10K used vehicle from a reputable source (versus a cash transaction in someone's driveway...)
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Comment Re:Efficiency (Score 1) 889

Consider replacing the electric commuter-car battery with a flywheel. We have the tech to do this for ranges of 50 miles or so.

Why would you, though? Flywheels have atrocious energy densities.

We should be thinking about replacing batteries with "fuel cells", because, like hydrocarbon engines, only fuel (most agree hydrogen is best) needs to be carried around, and the waste (H2O) can be dumped.

Wrong. A fuel cell car also needs a sizable battery, because a fuel cell capable of providing sufficient output for acceptable performance would be massive and expensive. A battery needs to be included to provide the peak power and the fuel cell basically acts as an on board generator to keep it topped off.

And given that, it's a waste. For all the solar energy you collected to make and process the hydrogen, you could have put that directly into an EV's battery and come out way ahead.
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Comment Re:Why not both? (Score 1) 239

if you're going to have an internal module that "generates whatever voltages are needed" then you're just going through the conversions again, and you're saving nothing on efficiency (and losing a lot on costs).

The only way it'll work is if the DC input, eg solar panels, is matched to the unit's requirements. Anything other than that and you're just running in circles.
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Comment Re:Solar Powered Aircon (Score 1) 239

Of course you can power everything with heat. Indeed, nearly everything *is* powered with heat; Most conventional power plants use thermal processes, converting heat energy into mechanical energy then into electrical energy.

A solar powered refrigerator (or any refrigeration cycle driven directly by heat) allows the use of fairly low quality heat sources to do useful work without losses converting it to electricity first. Very useful in some circumstances.
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Comment Re:Why not both? (Score 3, Informative) 239

And yet, in practice, HVDC is still more efficient than current AC lines in the end, even if still somewhat more expensive at the moment.

Yes and no.

AC power is far more efficient at higher voltage and short to medium distances, and you save a lot of material (and thus money) on conductor sizes. The voltage can be changed easily and it is safer and easier to switch on and off since there's 50 or 60 times per second where the voltage/current is zero - allowing for the circuit to be opened without arcing or inductive voltage spikes. AC arcs also tend to be self-extinguishing for this reason.

But AC systems also have inductance and capacitance to deal with. For very high power, very long distance runs, the capacitive losses start to add up. More current is required to charge/discharge this inherent capacitance, which means more power losses. This is where HVDC really shines.
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"Well, it don't make the sun shine, but at least it don't deepen the shit." -- Straiter Empy, in _Riddley_Walker_ by Russell Hoban

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