Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror

Comment Re:Hogwash (Score 1) 75

I respect the source you quoted (Union of Concerned Scientists). Here are some key findings from that paper:

"Nearly half (45 percent) of Americans live in BEST regions—where an EV has lower global warming emissions than a 50 mpg gasoline-powered vehicle, topping even the best gasoline hybrids on the market."

"Some 38 percent of Americans live in BETTER regions where an electric vehicle has the equivalent global warming emissions of a 41 to 50 mpg gasoline vehicle, similar to the best gasoline hybrids available today."

"About 17 percent of Americans live in GOOD regions—where an electric vehicle has the equivalent global warming emissions of a 31 to 40 mpg gasoline vehicle, making some gasoline hybrid vehicles a better choice with respect to global warming emissions.

Assuming constant miles per person driven across different regions, the average global warming contribution of BEVs works out to be equivalent to cars with 43-53 MPG fuel efficiency - significantly better than your original numbers, and good enough to legitimize green claims for BEVs in the US market.

Comment Re:Hogwash (Score 1) 75

It's true about electric cars in general, where I live in the USA they get about 35-40 mpg equivelant.

Source?

My i3 is rated at 138 MPGe (that's city driving which is 90+% of its use). As I said, carbon generated when recharging from a coal-burning power plant is far worse than that MPGe number suggests, but 35-40? Maybe in India (which burns mostly coal). Doubtful in the US.

City mileage for Teslas run about 2/3 that of the best BEVs. Still good mileage by most people's standards, and off the charts when compared with similar performance gas powered cars. The i3 vs. Tesla numbers turn around on the highway, with Tesla slightly outperforming the boxy BMW due to lower drag and stable speed (less acceleration of its extra mass).

In my experience efficiency for BEVs has a very different feel than gas powered. Regenerative braking is a small player in the overall efficiency of a car in real world driving - BMW claims about 3% energy savings. Academic papers show savings of up to 10% (presumably in repeated start-stop conditions) for normal electric cars, and better with special purpose vehicles. Getting back to my main point, an electric car's efficiency is far more dependent on drag and road incline than other factors. Quick acceleration kills a gas car's mileage, but barely affects my EV's range.

Comment Hogwash (Score 2) 75

Watch this video of BMW's I3 factory building new tech vehicles in a new tech factory. Now read TFA and learn that Divergent Technologies process doesn't use 3D-printing for the bodies (too heavy) or even the vast bulk of the chassis - the hyped 3D-process is for glorified lugs (they term them "nodes") used to build a tube frame. Consider the relatively tiny contribution of lugs to the assembly of a fully equipped car and it makes very little difference how those lugs are produced.

Then there's the claim that by printing different styles of lug (and some other parts, but not the bulk of the car) they can easily switch from building one type of car to another. If this is not wishful thinking intended to attract gullible investors, I don't what it is. To make effective use of this, they would need a super-agile assembly line stocked with most of the parts needed for all the vehicles they will possible build. The article admits that 3D-printing doesn't solve the majority of parts needs.

There's also the notion that by 3D-printing parts, replacement parts can be made on demand without special tooling. This is a very good point, and undoubtedly one that traditional car manufacturers are starting to look into, even for parts that may have been cast or otherwised conventionally produced for vehicle production.

Lastly, there's the anti-EV nonsense from Kevin Czinger, Divergent's CEO. Let me say that I believe his 1500lb natural gas-powered concept car has a lower environmental impact a Tesla SUV recharged off today's power grid. Today's electric cars are not a clear win when charged with coal generated electricity. Especially when you consider a heavy EV with very large batteries like that Tesla. The real promise of electric vehicles is their ability to use - and drive the development of - renewable sources of electricity. Green cars of the future will have to be both light and shun fossil fuels.

Comment Tensing is not the opposite of slouching (Score 2) 77

I agree that posture has significant effects on well being and how we are perceived, but the images I had as a kid of good posture were misguided. Military attention and finishing school book-balanced-on-your-head stiffness are not good example of ideal posture. They are too tense, stressing shoulders and lower back, among other things.

Good posture is balanced and flexible. Imaging partially hanging from a string attached to a point straight above the spine on the top of your head, with relaxed (not slouched) shoulders and back. Instead of rigidly holding a position and pivoting the body at one point, allow the hips and back, legs, shoulder, etc to adapt like an inverted pendulum to maintain balance -- not wiggly, just adaptable.

I hope this doesn't come off as too didactic, but it took me 50 years to begin to learn to move properly and it makes a big difference. At least for me.

Comment Re:I drink water (Score 1) 340

... the 132 gallons of water for a single cow... Surely lots of it goes back in to the system.

Good point! A lot of the 132 gallons used for processing a cow should be recoverable. That leaves just 999686 gallons per cow of harder to recycle water. Assuming 4,000,000 gallons of water per ton of beef and 500lbs of beef per "cow" (heifer/steer), that is.

Comment Re:Perhaps amend the definition of resonance (Score 1) 168

The resonance of the bridge wasn't involved at all. For resonance, the wind would have to match the resonant frequency of the bridge.

From the bridge's perspective, this was most certainly resonance! The air pressure field at the bridge's surface exerted force on the structure with a fundamental frequency very close to the bridge's resonant frequency.

Of course, flutter is a more complete explanation which considers the system of wind+bridge, rather than just the forces acting on the bridge. But isn't that obvious?

Comment Re:All electric for performance (Score 1) 254

Okay, so once you've flipped over the sack of groceries in the back seat with g-force and your kid in his car seat is crying because you jarred him. Has the novelty worn off?

For the most part, the car's price tag will keep it out of the hands of adolescent jerks*. One remarkable aspect of electric cars is that the torque is much more easily controlled than with an ICE. The car can be a pussycat with the accelerator at halfway and an amphetamine crazed tiger at full power. Also, Tesla has a button that selects between "Sport" or "Ludicrous" (or is it "Insane") acceleration modes. Hint: Use sport mode when driving kids home from the grocery.

You also just used a couple miles of your battery's energy. Hope it was 'cool' for you.

Get with the times -- we are not talking about gasoline power here. My electric car's energy usage per mile is highly dependent on drag and angle of climb, but does not change significantly whether I accelerate slowly or at full speed.

* Some of us are middle aged jerks. Oh, and the kid absolutely loves the acceleration of my car (BMW i3), which was good enough to break a motor mount (upgraded under warranty).

Comment Re:Higher voltages (Score 1) 147

Energy storage is proportional to voltage squared at constant capicatance? Really??? So if I connect two (super)capacitors in series, thereby doubling the voltage limit, I have somehow squared the energy storage! I don't think so!!!

Power goes up with voltage squared in resistive circuits, but that's a different issue. In this case, you'd get that power for a shorter time.

Comment Re:Lesson of the day (Score 1) 113

The algorithms at risk to quantum computing attacks (RSA, etc.) are essentially used just for key exchange. Unless you have an offline channel, you need these to communicate your one-time pad. Besides which, when using a one-time pad, the parties have to store it in at least two places before use, greatly increasing the time that these precious bits are at risk of being leaked or stolen.

Once key exchange has been accomplished, modern protocols rely on block or stream ciphers, which are not known to be vulnerable to QC attack.

Comment Re:Erm... (Score 1) 130

Unless the levelized price for renewable generation drops substantially below that of coal, I don't see how this will "spur renewable energy adoption" except for regions where electricity prices are substantially higher (e.g. Hawaii, $0.30/kWh)

Excellent point. Now... where can I get a 100 mile long extension cord for my electric car?

Comment Re:Environmentally friendly and sustainable? (Score 2) 130

How are batteries of environmentally friendly and sustainable?

Batteries are an enabling technology that can store intermittently available renewable energy for convenient use. Think wind powered cars and solar street lights, both can be made practical through the use of battery storage.

Comment Re:Spontaneous combustion (Score 4, Informative) 130

Uh... no.

"Lipo" (lithium-polymer) batteries are subject to thermal runaway (exploding into flame) if abused. Plus they can be more vulnerable for reasons including the typically soft packaging (OTOH, cell phones are not often bursting into flames in people's pockets). Maybe you were thinking of lithium iron phosphate (LiFePO4) batteries, which have lower voltage and lower specific energy density, but are more robust?

In any case, I thought *we* were discussing all sorts of batteries here, including a variety of lithium chemistries.

Comment Re:Shocking! (Score 4, Insightful) 171

Utility of a 2.8 second 0-60 time for most ICE car owners = 0.
Utility of being able to drive 500 miles and then 'recharge' in five minutes = lots.

Utility of having decent range and never having to stop at a gas station = priceless!

Seriously. Buy a second car (owners of this Tesla can certainly afford one). Or borrow a friends (they'll be happy to drive you Telsa for a day). Or rent a car for your trip. The convenience of having a fully charged car every morning more than makes up for any range anxiety I might have had, and my electric has less than half the range of a Tesla.

Slashdot Top Deals

HOLY MACRO!

Working...