There's a big difference between a lab demonstration (which, BTW, only gets the energy density of lead-acid) and a functional marketable product. I mean, if you want to count lab demonstrations then you should compare with lithium-air batteries at nearly the energy density of gasoline (plus with far higher efficiency).
The problem isn't ultracapacitors versus gasoline, it's ultracapacitors vs. batteries. And FYI, battery packs are major structural components of the vehicles. It's pretty hard for something that's such a major percentage of your vehicle's weight not to be. But that's generally in the casing - the goal is to protect the cells, not stress them on purpose.
Yes and no. Concerning storing energy in lead-acid batteries, no, that's too expensive (although it's been argued that used EV packs which no longer meet their rated capacity but still have tons of life in them might prove to be an excellent power storage banaza for utilities). It's done to some degree in isolated locations in specific circumstances, but to a very limited degree. There's also other types of battery storage done, for example, the vanadium redux station on one of the rattlesnake lines in Utah that they built to avoid having to build a second power line - but again, quite limited.
Much more widespread, however, is hydroelectric energy storage. You can of course ramp regular dams up and down to match the day and night cycle, and this is widely done - you're storing energy during the night to use during the day. More than that, however, is pumped hydro storage, where you actually pump water back at night. In some places, most notably in China, there are huge pumped hydro plants that don't even have a feed river, they're just two reservoirs that water is brought back and forth between to average out day/night consumption.
So, yes, it is done to some degree, but it's limited by your capital costs. The nice thing about EVs is that *consumers* pay the capital costs on the batteries for you. And when their vehicle no longer goes its full range near the end of its life, they consider that 70%-ish capacity battery trash.
I cover battery swapping later. The short of it, it's a non-starter.
You overestimate the cost of batteries, especially at fixed installations, and underestimate the cost of the other charging hardware. The charger's battery bank would probably run them about $0.15-0.2/Wh. So to fill even a max-range Model S (the one with the 85kWh pack, by far the largest) would be $17k (plus overhead). But multi-hundred-kW chargers themselves cost as much as a small house, they're not cheap.
Percentage-wise, battery charge/discharge losses are quite low, on the order of a couple percent. And you have to convert it to DC anyway, so that's a freebie.
Why is everyone obsessing with supercapacitors? They're the *expensive, low energy density* option. How can you talk about "cheap" and "supercapacitors" in the same sentence? And what's the reasoning for expecting them to get cheaper faster than batteries, when the opposite has been true?
Also, there's the issue of economics. A high power fast charger, say, 400kW, costs on the order of $100k and is the size of 1-2 soda machines. If you're only servicing 1-2 EVs a month, you're never going to pay for it. If we assume a 25 year lifetime and, after factoring in the time value to money assume that it needs to pay for itself plus, oh, let's say $50k of maintenance, during 15 years, then it needs to average $10k a year, or $28 per day, or $1.14 per hour. Since the charger provides 400kWh/h, then that'd be a surcharge of 0.3 cents per kilowatt hour at a 100% capacity factor, an amount that'd pretty much disappear under the 20 cents or so per kWh the power company would want to charge for being able to deliver such high powers at an irregular interval (you could reduce the rate by installing a battery buffer, but then you've got to pay for the buffer).
So, if the charger was always in use, its cost and maintenance would be vanishingly small. On the other hand, if it was in use 1% of the time, the costs for buying / maintaining the charger would run you 30 cents per kWh, significantly more than the cost of electricity itself, and bringing up the net total to more expensive than even gasoline per mile. Realistically, then, you need to get 3-5% utilization on your fast chargers for them to be economical.
400kWh is equivalent to about 1600 miles for a Prius-like electric car. 4% utilization of that means you need to average charging up 64 electric miles per hour. Meaning that you need one electric car that will need to stop at your station traveling down your route every hour. If we assume that you pick a spot where 1 in 3 EVs on the route will need to stop at your particular charger (you can't space them too far apart or people won't feel comfortable risking it, and not everyone is driving super-long distances), then you need 3 EVs going down your route per hour. You need to cover the whole interstate highway system, so the limiting factor will be the less densely trafficked areas. However, you don't need to cover every road that densely, just the busiest ones in a given region. Some whole regions don't beat more than a dozen or so vehicles per hour, so let's set 15 vehicles per hour as our threshold to reach everywhere. This means that you need 20% of them to be EVs to meet the 3 EVs per hour requirement. If we assume that gasoline vehicles are twice as likely to be driven on long distances out in the boonies as fast-charged EVs, this number rises to 40% of vehicles needing to be EVs. America has 250 million vehicles, so to reach that percentage threshold, that means 100 million EVs total. So that's the critical EV penetration needed to economically justify fast charging stations that would let you drive to every part of the US.
Now, of course, that's to drive *everywhere*. There are long stretches, long enough that EVs would need to charge, that receive tens of thousands of vehicles. At 1.5k vehicles an hour, the US needs only 1M EVs on the roads (if equally distributed) to justify a fast charging network in these areas. Areas with that kind of traffic are rather limited, however. The vast majority of the US could be reached by 150 vehicles per hour roads. This requires a total EVs on the roads of 10M.
US consumers buy a total of about 16 million vehicles per year.
One can change the operating assumptions to get different results. If you let chargers be more sparse, then a higher percentage of drivers will charge at a given charging station, increasing its utilization (the downside is EV drivers would be less likely to drive there). One could argue that EVs will be less than half as likely to be driven long distances as gas cars even with fast charging, which will almost certainly be true in the beginning, although the inverse will probably be true in the future. And of course one could argue over what sort of costs drivers would accept as tolerable or the exact pricing of power, chargers, maintenance, etc. For example, one could probably argue that while most people wouldn't toler
Finally - EVs will become practical. Hopefully this leads them toward working together to develop ultracapacitors that charge in seconds to a couple of minutes so it can be a true ICE replacement
So you're talking about an ultracapacitor instead of a battery? Yeah, good luck with that. Ignoring the price issue, they're struggling to even get up to lead-acid energy density.
Li-ion cells have no problem taking fast charges. Some types can even charge in a couple minutes without problem. The issue comes when you build a whole pack out of them: cooling. Most types of li-ion cells are in the ballpark of 98-99+% efficient when slow charging. When fast charging it drops, depending on the chemistry, usually somewhere in the ballpark of 93-98% efficient. Let's say 97%. So 3% of your energy input is heat. Let's say your car consumed 250Wh/mile, your typical Prius-level streamlined vehicle consumption. Let's say you want a 200 mile charge in 5 minutes. That's 50kWh in 5 minutes, or 1 MW. 3% waste heat isn't much, but when your input is *1 MW*, that's 30 kW of waste heat. A small plug-in space heater is usually around 1,5kW, so that's the output of 20 space heaters. See the problem? To pull off *really* fast charges like that, you can't really just look at what the individual cell tolerates. You have to quickly be able to dump the waste heat to a cooling fluid, which is an engineering problem, and you need cells that maintain very high efficiency during high-rate charge, which is a chemistry problem. Also at those sort of powers you have to even cool your wires, both on the charger and in the vehicle (an uncooled charger cable capable of delivering 1MW would be so heavy you couldn't lift it). Personally I think the high power charging standard should simply be set up suchly that the charger supplies the vehicle with coolant on a closed-loop cycle, so the vehicle doesn't have to haul around a massive cooling system, the vehicle would need little more than cooling ducts. But who knows how things will end up.
and allow for a small swappable ultracapacitor so that if your battery goes flat a few miles from a charging station all you need is a state trooper or AAA and exchange a capacitor to get the car going long enough to reach a charger
First off, why are you proposing both couple minute charges *and* swap? Swap is designed to be an alternative to fast charge. But as challenging as fast charge is, swap is even worse. These packs aren't little lead-acid starter batteries, they're many hundreds of pounds, upwards of half a ton or so, and form an integral part of the vehicle's structural integrity. And they're very valuable, too, people aren't going to want to get stuck with a crummy one. And even *if* the auto industry had a track record of collaborating on standards, which they absolutely don't, just the widely differing weight distrubution / form factor / power output requirements / capacity requirements / etc for different vehicles would demand each swapping station storing a massive range of different types of packs. All this ignoring the actual engineering challenges involved. It's just totally impractical. And I can tell you what's definitely NOT going to happen, a state trooper just walking up and swapping out something many times his own weight that makes up an integral portion of the vehicle.
Note, mind you, that the concept of getting a "jump" on an EV isn't a far-fetched idea, that is completely workable. You could even limp to the nearest farmhouse and slow-charge on regular wall power until you've got enough juice to make it to the nearest charging station. But swapping out the battery on the side of the road? That's like saying "replace your engine on the side of the road".
except possibly as a backup generator - like the Volt, i3, i8, etc.
So the vehicle is supposed to have fast charge *and* swap *and* be a PHEV? Why on earth? You realize that each one of those things has its own major cost, maintenance, size, and mass associated with them? And thus consequently disadvantages all of the others?
The real problem is that they didn't standardize on high-power charging in the beginning. We got the SAE J1772 standard, but it tops out at 80 amps / 240V. Europe's a mess as it stands, with a bunch of competing connectors implementing IEC 62196-1, and again, no solid fast charging standard. This leaves everyone to have to pick and choose their own high-power coupler. It's idiotic, they should have standardized from the beginning, it's obvious that it's going to be a necessity for mainstreaming EVs. 20 minutes to charge your car while you take a lunch stop, fine. 3 hours to charge your car while you take a lunch stop, Not Fine(TM). Until you get fast charging standardized and available, the majority of consumers will continually hold that up as their excuse as to why they can't buy an EV (there's often some big holes in that logic, but that's neither here nor there).
There are a couple other possibilities for mainstreaming other than fast charging, but I don't see them around the corner. One is to have a whole day's worth of driving - or most of a day's worth (enough that if you charge during your meal / rest breaks, it's a full day) - on a single charge. In such a case, the upper end of J1772 is enough for all but very high consumption vehicles to charge you to full while you sleep, so you can drive another full day immediately after. But that requires multi-hundred kilowatt hour packs which would weight 1-2 tons and cost $50-100k with today's tech. It'll happen eventually, batteries double in energy density every 8 years or so (price drops happen too but they're more irregular and harder to predict) - but we're not to the point yet where this would be a viable option. The other option is making available self-steering genset trailers, like the AC Propulsion Long Ranger. It seems such an obvious stopgap - you've got a generator when you need it but don't have to drag it around when you don't, you could buy them, rent them, share them, etc. Your car uses gasoline on those occasional long trips but otherwise is pure electric with none of the problems of PHEVs. Unfortunately no major automakers are pursuing this approach (I'm not really sure why, the Long Ranger got good reviews). As it stands, the majority of manufacturers are pursuing some form of fast charging, but as mentioned, the standards situation is a mess right now. :
And then there's the issue of how fast charging changes incentives. As it stands, utilities *love* EVs because it lets them sell more power for rather little added infrastructure cost, they're largely stable nighttime loads. But once you start getting to 480V multi-hundred-amp daytime fast charges, it's just the opposite, that's horrible for them. It's possible to make them become once again something desirable for utilities by including a battery buffer inside the charger (trickle charges when not fast charging a car, then burst discharges), but I'm not aware of any fast chargers that come like that by default.
The other option is to accept that disadvantage of allowing fast charging EVs in exchange for having EVs smart grid integrated, so that all the cars left plugged in during the day charge when demand is low and stop charging or even reverse flow during those brief peaks. It's possible to incentivize EV owners as well - let them pick at what time their car needs to be fully charged, whether they want to allow reverse flow, etc. The more flexible they are about timing, the more their car can wait to buy power when it's cheapest, and they could get a rebate on reverse flow power sold at higher prices during peaks. Such a system would work well, leaving owners with the ability to choose the balance between speed and price (even potentially to earn a net profit on their car if they're flexible enough), and it'd leave utilities with a nice smooth generation/demand balance, much better than today. Unfortunately, neither the grid nor current EVs are to that point.
It *was* anti-soviet. That was its design purpose - to fight the soviets if they got into Europe. The only "evidence" trying to claim it was anything other than a group of anti-soviet cells who got out of hand in a couple countries was a bogus "army field manual" created by the KGB as a psy-ops. And if you have a better all-encompassing term than immoral, fine, substitute whatever word you want. I didn't want to just single out the bombings by the Italian right-wingers.
Is that a joke? The "gas deal" certainly provides cheap gas all right - so cheap that there's essentially zero profit in it for Gazprom. It's a real testament to how desperate Russia is to not look like they're dependent on the EU to buy their gas. Check out a map of Russian gas pipelines. Notice the complete lack of any pipelines anywhere near China's major cities. The gas deal leads from an undeveloped field through a nonexistent pipeline through nonexistent processing facilities. The pipeline isn't supposed to come online until 2020, and the main field until 2021. And that's assuming they can actually build it, which given their track record while *not* under sanctions is a big "If". And even if all that transpires, it's still a small fraction of their EU gas exports.
Anyone who actually looks at the "deal" can easily see it was just a PR move.
The concept that Russia can just turn east to China is beset by the fundamental problems that Russia doesn't have infrastructure connecting itself well with China, the vast majority of their people live nowhere near China, the vast majority of their industries are nowhere near China, and so forth. Russia is set up to function as part of Europe. And if it came down to it, does anyone in their right mind think that if the EU and US basically told China "us or them", they'd choose Russia, rather than the vastly larger markets of the US and EU that China's already intensely integrated with?
Not like the "breakup" with Russia would be painless for Europe. They'll be paying higher oil rates and significantly higher gas rates, plus higher rates for a wide variety of raw materials. But the situation is highly lopsided; Russia's GDP is an eighth the size of Europe's, a 16th the size of Europe + US. Whatever reduction in trade that hurts the EU / US hurts them an order of magnitude worse, barring huge multipliers on their part. Their manufacturing sector, in particularly high tech goods, is grossly undersized for the size of their population, and that's very unfortunate because such goods (in particular industrial goods, spare parts, etc) are often not fungible. They're also highly dependent on food imports (at least those are fungible).
Gladio had what to do with private corporations? It was an anti-soviet guerilla-prep program run by NATO in every country in Europe, wherein later a few groups got infiltrated by right-wingers who tried to use their power in immoral manners. But that doesn't stop a particlar brand of conspiracy theorist from crediting to Gladio everything under the sun.
Maglev trains are a whole different issue. You really can't go at those sort of speeds using wheels. It's hard enough to manage the sort of speeds that the Shinkansens go with wheels. Maglev is a great solution to the problem, in that it totally works and is quiet efficient. Not so great in that it costs the GDP of a small county for a couple dozen mile track, mind you.
I know I'd get jumped for saying it, but I think Hyperloop fits the typical use case for Maglev far better... ground-effect air cushion in a rarified atmosphere, and your track is just steel tubing on columns with a load-bearing requirement no greater than that of Disney's monorail.
It's hard to listen when, up until your last post, you weren't talking. "No, you're not understanding what I'm picturing" is not a criticism until you actually state what you're picturing.
What's the loss in compressing air in a sealed piston?
It depends on the rate of heat flow. The act of compressing or decompressing 6x or more produces a great amount of heat. This flows into the walls of your container, trying to equalize with the ambient temperature.
Applying this to your tire example, we consider two reservoirs, one the tires and one an extra temporary storage tank. Since volume remains constant (isovolumetric process) and pressure increases 6x, under the ideal gas law temperature of the working gas increases 6x inside the temporary reservoir and decreases 6x inside the tires. Assuming no heat transfer, that's down to a chilly 50K in the tires and a burning 1800K in the cylinder. This, of course, doesn't happen in the real world, because with these temperature differentials with the outside world, you experience rapid heat flow to equalize with the surroundings. And there's no shortage of time for this equalization to occur (while you can insulate your gas reservoir, you can't practically insulate your tires). A typical acceleration or deceleration profile will be on the order of 10-20 seconds. How well do you think the gas inside the tires would remain at 50K over a 20 second interval versus rubber that's even hotter than ambient air? In practice, the heat from the air in the tires will almost completely equalize with its surroundings. As the temperatures equalize, the pressure rises in the tires and falls in the reservoir, depleting the pressure differential that the system is counting on to put the air back into the tires.
Now, I would be curious as to your counter to this, except...
You object on a theoretical basis, so the implementation doesn't matter until you learn basic physics. Let me know when that's done
Let me know when you decide to stop being an asshole when discussing things on the net.
In no manner does that reduce visibility. I can't even envision how you're imagining that that reduces visibility. Some car dashes are level, some slope up, some slope down, this isn't at all radical. You have your dash begin below the windshield and intercept it at an upwards angle, just like is done in thousands of cars already.
No, it's not. When they build buildings and want the strongest foundation, they use straight vertical piers
No, in general, the strongest shape for a building for a given amount of material is an arch in the 2 dimensional case, a vault in the 3 dimensional case. For overall loadbearing of an evenly-spread load, the strongest shape (in terms of minimizing bending forces) is a parabolic dome, which reduces bending stresses to zero and maintains a purely compressive load, which is generally much easier to withstand. Modern buildings use straight lines to minimize their footprints, not because they're stronger. Seriously, have you ever looked at the shapes people had to use to build large buildings before the advent of modern materials? Hint: they're not big boxes.
The more your interior structure is solid - aka, if you have an internal skeleton - the less important an arched / vaulted structure is, as you have a more even distribution of lateral forces. On the other hand, if you have a large interior space supported entirely by its exterior, it's very hard *not* to use large arches / vaults, even when dealing with modern building materials (think it's a coincidence that very large enclosed sports stadiums are domed?). And guess what? Cars are a large interior space supported entirely by its exterior, using as little material as you can get away with.
So tying two balloons together (so air can pass) and squeezing one to move air into the other is a lossy process?
Are you talking about two pressurized or unpressurized balloons where you're creating a tiny pressure differential between them? Because it's the act of increasing the pressure that's the highly lossy process. And your ballons are never going to flow from low pressure to high.
No, you are so obsessed with being right that you stopped thinking.
How about instead of dancing around the topic, if you think I'm misunderstanding what you're envisioning, you actually describe in detail what you're envisioning? I'm just simply telling you, if you're compressing a gas, it doesn't matter if you're recovering or storing energy during the decompression, the compression itself is highly lossy. You can recover 100% of the stored energy of the compressed air and it still leaves you with major energy losses.
Describe how you're getting the tires back up to 120+ psi.
How do you clean the small angle where the dash and windscreen meet?
You angle the dash up to the windshield. Nobody says the dash has to meet the windshield at the same angle the windshield is raked at.
What is the effect at night, since you are looking through more glass and at a more distorting angle?
My rear window on my Insight is even more raked than the optimal front window on a streamliner, there's no distortion.
Extending the A-pillar along your raked windshield makes it almost worthless for rollover protection.
How on earth are you coming up with that one? The elongated egg-shape of the front end of a streamliner is one of the strongest shapes in nature, and the A-pillars follow the shape. The Aptera 2e had a 4,5x higher roof crush strength than the federal car mandate - a much more impressive figure than their door crush strength, which was only about 2x the federal car mandate.
No, it simply is lossy, period. Air compressors are geneally at 10-20% efficienct, usually under 15% for small one. To get any sort of significant improvement on that you have to add in one or more bulky waste heat recovery cycles (yes, thermal engines), which are limited by Carnot's law, which dramatically limits your recovery potential.
It's not "confirmation bias", it's a fact; air compression is a highly lossy process. If you don't believe me, ask anyone else who has experience with compressors. Or just google it.
I'm sorry if you don't like the fact that your proposed solution is vastly inefficient. But it IS vastly inefficient.
Oh, forgot to mention - Aptera 2e's drag coefficient was 0,15. It could cruise at a steady 55mph on 80Wh/mi, a bit more than the power of two blow driers.
Well, one of the most extreme examples was the "car" I was on the waiting list for, Aptera's 2e, which was about 2 months away (I have their old internal corporate schedules and checklists) from shipping to customers when the board brought in Paul Wilbur to manage the company. Wilbur is a Detroit car exec who had ran one company into the ground after the next; the first thing he did after taking over the company was order a redesign nearly the whole vehicle trying to "mainstream it". The changes ruined the vehicle and he burned through all the company's money in short order (including taking a large salary for himself), bankrupting it. Yes, I'm still bitter over that.
( And yes, I fully realize that I vehicle *that* streamlined isn't for everyone;) )
For cars that have shipped in some degree of volume, the EV1 really stands out. While both with less interior room and higher drag than the Aptera Mk1, it still sported an impressive 0,19 drag coefficient and 0,36m^2 frontal area. About 1500 were made. Another low volume but from way back was the Tatra 77, with a drag coefficient of 0.212. Not bad for 1935! The Mercedes CLA has a drag coefficient of 0,22; I'm not sure of the volume. The Tesla Model S's drag coefficient is 0,24; it's new but they've already delivered tens of thousands. The first-gen insight (what I drive) was 0,25; there were 17k sold. However, also at 0,25 are the Sonata Hybrid, the Audi A2, the Lexus LS 430, the Pugeot 508, and the Toyota Prius. So all together you've got millions of those.
Now, a lot of those aren't low in frontal area, just drag coefficient. But frontal area is something that also provides benefits (interior room); a high drag coefficient doesn't provide benefits, so reducing that figure matters the most.
The EV1 was indisputably both the most advanced and most popular electric offering at the time, and most critically, they basically gutted all similar research and sold off their patents, not even pursuing hybrids. Their selling off of the patent rights also made it impossible for several other companies to have continued their EVs even if they had wanted to. GM was also the most active and public of companies trying to kill off the ZEV mandate. So all together, it's not surprising that they earned the lion's share of the puiblic scorn on that one. The next most popular of the ZEV-mandate EVs, the RAV4 EV, wasn't taken away from its owners, and for a decade the few that remained were the best EVs available on the market and commanded ridiculous prices relative to their age and hardware specs. The Ford Ranger EV was pretty primitive, and they too were willing to sell to owners.
The EV1 really was an amazingly advance vehicle for its age. It was one of the first aluminum-framed production cars from a major automaker. It had a then-recod low drag coefficient of 0,19 *and* a very low cross-section, something aero-lovers like me adore. It was so streamlined that a prototype that GM re-geared but otherwise used the same chassis and drivetrain hit 183 mph. The drivetrain was miles ahead of its competitors, a highly efficient AC inductive motor that could handle both accel and charging from the same system; the drivetrain of the Tesla Roadster is a direct descendant (Impact -> EV1 -> tzero -> Roadster). The EV1 had all sorts of features that are now common but were rare or unique at the time, including a control computer that could be programmed to do scheduled tasks, for example, to preheat/cool the vehicle at a scheduled interval. Speaking of climate control, the EV1's was more advanced than that of most EVs today, using a bidirectional heat pump for both heating and cooling along with waste heat recovery, with heat augmented by a resistive heater.
While it was out there, GM wanted the public quiet involved with the EV1. They plugged it in ads, using it as a "look at us, we're high tech" vehicle. But they never wanted to have to build it in the first place, and they seriously bungled the PR during the termination. When the guy who ordered its termination called it his biggest mistake, the guy who presided over GM during its march to bankruptcy, that's a major statement.
I'm not talking about a long hood so much as a tall hood relative to the rest of the vehicle - the car starts, then suddenly it's nearly as tall as the roof. Example: here's the concept mode for the Chevy Volt. I took one look at it and smacked my head, anyone who knows aerodynamics can see that that thing is going to have the aerodynamics of a rolling brick (spoiler: that's a whopping 0,43 drag coefficient on a supposedly "efficient" car!). Nobody should have been the least bit surprised when it changed dramatically going from concept to production. Yet that concept look is supposed to mimic the look of a "chopped" car (despite not reducing the frontal profile) and thus be "sexy", "muscular-looking" and desireable. It just ruins it for me. I know that I'm weird in being turned off from a car by seeing its awful aerodynamics.
Basically, there's no reason that your "long hood" has to quickly flare to full width/height in the front, then remain relatively constant height up to the windshield. That's highly suboptimal for aerodynamics and achieves nothing in terms of giving you a long distance to decelerate in. The optimal aerodynamic front end is roughly elongated-egg shaped.
Beyond that, you don't need a long hood at all, either, for crash protection, just a long deceleration distance. Hood length and deceleration distance, though related, are not equivalent. One factor, for example, is where the driver / passenger are located inside the vehicle. If you have a highly raked windshield (optimal aerodynamics) then the driver and passenger have to be located a bit further back from the front of the car for headroom reasons, so there's still plenty of room ahead of them to the foremost point on the vehicle. Also at play is how the vehicle deflects force in an accident - whether it crumples straight back or whether the nose rides up during a collision (the latter gives extra deceleration distance). A greater rake on the windshield also decreases the chance of windshield penetration.
It should also be pointed out that such a design also enhances pedestrian safety in a number of respects. The lack of an abrupt flare means a pedestrian is more likely to be hit at an angle and accelerated over a greater length of time (reduced G-forces). The matching rake between the hood and windshield additionally means they're not going to suddenly decelerate at the windshield. To be fair, of course, some pedestrial-safety features, such as low bumpers, run counter to aerodynamics.
As for that SkyTran PRT: Judging from the image on the cover, it looks like a reasonably good shape up front, but the rear end sucks. Contrary to popular misconception, it is *not* good to have a rounded rear end. Once your angle gets too steep, the flow will detach from your vehicle, leaving a low pressure wake. You want to not exceed the critical angle (aka, use a roughly constant taper angle) and prolong the detachment as long as you can (aka, as gentle of a taper as your design parameters allow), and when you can't delay the detachment any more, you want a relatively abrupt cutoff, potentially with a vortex generator to draw down the stream. The actual details vary depending on the situation, and one always needs to do CFD work, but that's a rough "in general" for aerodynamic optimization
Update: I searched more and found some rather different looking PRT images. These are of an excellent aerodynamic form, with an appropriate taper in back (though I personally prefer a vertical taper to a horizontal taper for cars... theirs makes sense for their particular application, however). I'd be willing to wager that their cover image was an early artistic concept, while the latter was something they actually did CFD work on.
It could be (though that would have engineering challenges of its own, and not just noise minimization), but remember that compressing air is a rather lossy process. If you're rapidly dropping the pressure, say from 120psi to 20psi then back, every time you need traction, you're going to lose an awful lot of energy doing so.
Given that increased camber is often a good thing when cornering, and that there's no inherent physical loss mechanism in changing camber, and your required hardware to do so isn't particularly onerous, that's why I mentioned that particular possibility. But overall, that was just an example; the key point is, there's an order of magnitude difference in rolling coefficients between today's car tires and that of rigid wheels**. If you can get rid of all of the compression/flex in your general-use case, and only add it in when you need the additional traction, and make use of a vibration isolation or active cancellation system to maintain ride quality, you could virtually take rolling losses out of the picture.
** - I should clarify that when I say "rigid wheels" perform an order of magnitude better, I don't simply mean "anything non-pneumatic", but rigid to the degree of train wheels or ball bearings. For example, in wheelchairs, pneumatic tires often actually have *lower* rolling losses than "rigid" wheelchair wheels; the latter flex too much and thus lose more energy in the process than their pneumatic equivalents. It's not the use of air that's the problem, it's the repeated bending of material, turning your kinetic energy to heat. To achieve dramatic improvements in rolling coefficients over conventional tires, a rigid wheel needs to offer dramatically less flexure than its equivalent tire as it rotates. But it also has to be lightweight to minimize total mass and in particular unsprung mass. Hence the suggestion of carbon fiber / foam core wheels; I would expect such wheels to be able to meet that kind of spec if built well enough. But who knows without experimentation...
It's also a fair criticism that once you start going for such extreme rolling drag reductions, imperfections in your road surface are going to have an increasingly large impact on your achieved rolling coefficient.
Oh, and just an additional comment, from my past experience in the auto industry: this wasn't an "oops, I wasn't supposed to say that!" remark. The Japanese companies are in general very good at controlling information flow; this was clearly planned for him to say that. But the reason he said it was almost certainly not to prepare people for the coming day of flying cars; it's about perception. It's a major brand positive for an auto maker to be perceived as high tech / cutting edge / innovative, and they want to culture that.
Remember Rick Wagoner, the guy whose tenure at GM made a graph of the company's stock look like a double diamond ski slope? Of all of the things that he could have regretted, he's stated that the number one thing he regrets was axing the EV1 (late 90s electric car) program. The EV1 lost tens of thousands of dollars per unit and there weren't many made so there was major overhead on top of it; but by axing the program to save a little money, they willingly gave up the perception of being a tech innovator, right at the time the Japanese companies were introducing hybrids. Even to people who weren't considering buying a Prius or Insight - aka, the vast majority of consumers - the very perception that Toyota and Honda appeared to be high-tech innovators demonstrably influenced consumer buying decisions.
Car makers have slick PR teams who survey and carefully try to manipulate the public perceptions about themselves to influence buyer behavior. Expect that the decision to mention this came straight from one of them.
First off, in general to get up to 95%, you're talking "racing supercars" territory. But honestly, not even that (see below).
Secondly, the aero and rolling drag equations (in particular, rolling) are just approximations, along the lines of "assume a spherical cow". The real-world deviation from the formulas is usually described as changing drag coefficients under different conditions, but in the case of rolling drag, it changes so much at high speeds due to increasing magnitude standing waves on the tires (greater rubber flex) that it's better to add into the modeling a nonlinear component; it's not at all accurate to say that it's "pretty much constant". If you don't at least use a piecewise formula for the rolling coefficient in your vehicle energy consumption calculations, you get results that are way off.
In practice, even at supercar speeds, you'll never get up to that mythical 95% aero drag. Rolling drag is also greatly affected by a number of other properties besides velocity, including road surface, tire pressure, tire temperature (rolling resistance drops as you drive as the internal pressure rises), and road condition (contrary to popular myth, in light rain conditions, the main increase in rolling drag is due to tire cooling, not due to pushing water out of the way).
Oh, and I've neglected to mention thusfar parasitic / operating losses as another vehicle energy loss mechanism, which also play a role (usually small, but sadly growing), which makes it even harder to have aero be such an overwhelming percentage of the picture as was previously claimed. (there's also braking losses, but they're primarily an in-town thing)
My presumption is that they're still using wheels for acceleration. For example, in a front-wheel drive car, you could hover the back wheels, at least until you need traction from them (for example, turning). With a pulse and glide configuration, you could even hover the drive wheels for a good chunk of the time.
Still, I think there's much better options for reducing rolling drag.
That's not true. It varies from vehicle to vehicle and between driving profiles, but it's usually 50-75% of the resistance at highway speed coming from aero drag - not 95%. Rolling drag remains a significant loss factor at all speeds.
That said, this doesn't sound to me like the most logical approach to tackle rolling drag - wheels are more efficient than hover as-is in most general-use cases, and I can easily envision a lot more that could be done. For example, you could use very high pressure (120+ psi) tires with a hard, thin central tread, relying on automatic camber to a thick, sticky side tread during accel, braking, cornering, or when traction control kicks in (the additional vibrational load from cruising on high PSI tires could be canceled with, for example, a cable vibration isolation system or active vibration cancellation). Such a system should be able to approach the rolling coefficients of hard steel wheels (a tenth that of traditional car pneumatic tires - effectively rendering rolling losses irrelevant). Heck, if you're going to that extent, it's not much further to go all the way to completely solid wheels (though you'd want foam-core carbon fiber or similar to keep the weight and in particular unsprung mass down, not solid steel) and not even have to deal with tire inflation or puncture risk. So long as you have a way to automatically shift to a thick, sticky tread as needed based on current traction conditions and have a mechanism to soak up the higher vibrational loads to maintain ride quality, you're fine.
Is that a pretty huge deviation from standard practice? Yeah, by no small amount, it's literally reinventing the wheel. But you know what, it's also a pretty huge deviation to have cars outright hover on the highway.;)
But yeah, you're right in that rolling losses aren't the *primary* loss mechanism on the highway. A lot more has to be done to tackle aero drag, and that's trickier - not least of which because the optimal shape varies based on speed and things like crosswinds (and the more you optimize your shape, the bigger of an issue this becomes). One of the more clever ideas I've seen - I don't know how it'd play out in the real world, mind you - was Aptera's plan to take a page from Gerald Bull's playbook and fill in the low pressure wake with air ducted in through the cabin. There's also a fair bit of research designed for aircraft (where aero drag is an even bigger issue) that could translate to cars, for example, skin textures or microstructures designed to maintain laminar flow or reduce surface drag. One of the more exotic variants of that which I've seen is a taut film outer-layer over a microscopic layer. The film vibrates in the wind between its ridges, setting up standing waves which separate the laminar flow from the surface, reducing the flow speed in contact with the surface and thus reducing direct surface drag. There've been peer-reviewed papers on it, and one of the researchers founded a company that now makes kits to reskin a variety of small aircraft (not very many thusfar, the skin has to be custom designed for each model). That's of course just one example among many, it's a very active field of research, as even a fraction of a percent reduced aero drag on a commercial airplane results in massive fuel savings.
Honestly, I'll be happy if we can just get people's style preferences to shift away from naturally high-drag forms like those ridiculous oversized front-end things where you can barely see over the hood. I know I'm out of the mainstream, but I love the look of aerodyamics. Real aerodynamics, not counterproductive curvy features that a lot of people think are "aerodynamic" but actually raise your drag. I want my car to look like a wingless plane, a car that cuts through the air like a knife rather than a clobbering oaf shoving it all around as it drives by ("Excuse me air, coming through, excuse me, sorry there!"). I want a rounded front end and a rear end that tapers vertically down with as long of a t
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9200 miles per year isn't that much below the US average. Just because you drive freakishly much doesn't change that.
There's a big difference between a lab demonstration (which, BTW, only gets the energy density of lead-acid) and a functional marketable product. I mean, if you want to count lab demonstrations then you should compare with lithium-air batteries at nearly the energy density of gasoline (plus with far higher efficiency).
The problem isn't ultracapacitors versus gasoline, it's ultracapacitors vs. batteries. And FYI, battery packs are major structural components of the vehicles. It's pretty hard for something that's such a major percentage of your vehicle's weight not to be. But that's generally in the casing - the goal is to protect the cells, not stress them on purpose.
Yes and no. Concerning storing energy in lead-acid batteries, no, that's too expensive (although it's been argued that used EV packs which no longer meet their rated capacity but still have tons of life in them might prove to be an excellent power storage banaza for utilities). It's done to some degree in isolated locations in specific circumstances, but to a very limited degree. There's also other types of battery storage done, for example, the vanadium redux station on one of the rattlesnake lines in Utah that they built to avoid having to build a second power line - but again, quite limited.
Much more widespread, however, is hydroelectric energy storage. You can of course ramp regular dams up and down to match the day and night cycle, and this is widely done - you're storing energy during the night to use during the day. More than that, however, is pumped hydro storage, where you actually pump water back at night. In some places, most notably in China, there are huge pumped hydro plants that don't even have a feed river, they're just two reservoirs that water is brought back and forth between to average out day/night consumption.
So, yes, it is done to some degree, but it's limited by your capital costs. The nice thing about EVs is that *consumers* pay the capital costs on the batteries for you. And when their vehicle no longer goes its full range near the end of its life, they consider that 70%-ish capacity battery trash.
I cover battery swapping later. The short of it, it's a non-starter.
You overestimate the cost of batteries, especially at fixed installations, and underestimate the cost of the other charging hardware. The charger's battery bank would probably run them about $0.15-0.2/Wh. So to fill even a max-range Model S (the one with the 85kWh pack, by far the largest) would be $17k (plus overhead). But multi-hundred-kW chargers themselves cost as much as a small house, they're not cheap.
Percentage-wise, battery charge/discharge losses are quite low, on the order of a couple percent. And you have to convert it to DC anyway, so that's a freebie.
Why is everyone obsessing with supercapacitors? They're the *expensive, low energy density* option. How can you talk about "cheap" and "supercapacitors" in the same sentence? And what's the reasoning for expecting them to get cheaper faster than batteries, when the opposite has been true?
Also, there's the issue of economics. A high power fast charger, say, 400kW, costs on the order of $100k and is the size of 1-2 soda machines. If you're only servicing 1-2 EVs a month, you're never going to pay for it. If we assume a 25 year lifetime and, after factoring in the time value to money assume that it needs to pay for itself plus, oh, let's say $50k of maintenance, during 15 years, then it needs to average $10k a year, or $28 per day, or $1.14 per hour. Since the charger provides 400kWh/h, then that'd be a surcharge of 0.3 cents per kilowatt hour at a 100% capacity factor, an amount that'd pretty much disappear under the 20 cents or so per kWh the power company would want to charge for being able to deliver such high powers at an irregular interval (you could reduce the rate by installing a battery buffer, but then you've got to pay for the buffer).
So, if the charger was always in use, its cost and maintenance would be vanishingly small. On the other hand, if it was in use 1% of the time, the costs for buying / maintaining the charger would run you 30 cents per kWh, significantly more than the cost of electricity itself, and bringing up the net total to more expensive than even gasoline per mile. Realistically, then, you need to get 3-5% utilization on your fast chargers for them to be economical.
400kWh is equivalent to about 1600 miles for a Prius-like electric car. 4% utilization of that means you need to average charging up 64 electric miles per hour. Meaning that you need one electric car that will need to stop at your station traveling down your route every hour. If we assume that you pick a spot where 1 in 3 EVs on the route will need to stop at your particular charger (you can't space them too far apart or people won't feel comfortable risking it, and not everyone is driving super-long distances), then you need 3 EVs going down your route per hour. You need to cover the whole interstate highway system, so the limiting factor will be the less densely trafficked areas. However, you don't need to cover every road that densely, just the busiest ones in a given region. Some whole regions don't beat more than a dozen or so vehicles per hour, so let's set 15 vehicles per hour as our threshold to reach everywhere. This means that you need 20% of them to be EVs to meet the 3 EVs per hour requirement. If we assume that gasoline vehicles are twice as likely to be driven on long distances out in the boonies as fast-charged EVs, this number rises to 40% of vehicles needing to be EVs. America has 250 million vehicles, so to reach that percentage threshold, that means 100 million EVs total. So that's the critical EV penetration needed to economically justify fast charging stations that would let you drive to every part of the US.
Now, of course, that's to drive *everywhere*. There are long stretches, long enough that EVs would need to charge, that receive tens of thousands of vehicles. At 1.5k vehicles an hour, the US needs only 1M EVs on the roads (if equally distributed) to justify a fast charging network in these areas. Areas with that kind of traffic are rather limited, however. The vast majority of the US could be reached by 150 vehicles per hour roads. This requires a total EVs on the roads of 10M.
US consumers buy a total of about 16 million vehicles per year.
One can change the operating assumptions to get different results. If you let chargers be more sparse, then a higher percentage of drivers will charge at a given charging station, increasing its utilization (the downside is EV drivers would be less likely to drive there). One could argue that EVs will be less than half as likely to be driven long distances as gas cars even with fast charging, which will almost certainly be true in the beginning, although the inverse will probably be true in the future. And of course one could argue over what sort of costs drivers would accept as tolerable or the exact pricing of power, chargers, maintenance, etc. For example, one could probably argue that while most people wouldn't toler
So you're talking about an ultracapacitor instead of a battery? Yeah, good luck with that. Ignoring the price issue, they're struggling to even get up to lead-acid energy density.
Li-ion cells have no problem taking fast charges. Some types can even charge in a couple minutes without problem. The issue comes when you build a whole pack out of them: cooling. Most types of li-ion cells are in the ballpark of 98-99+% efficient when slow charging. When fast charging it drops, depending on the chemistry, usually somewhere in the ballpark of 93-98% efficient. Let's say 97%. So 3% of your energy input is heat. Let's say your car consumed 250Wh/mile, your typical Prius-level streamlined vehicle consumption. Let's say you want a 200 mile charge in 5 minutes. That's 50kWh in 5 minutes, or 1 MW. 3% waste heat isn't much, but when your input is *1 MW*, that's 30 kW of waste heat. A small plug-in space heater is usually around 1,5kW, so that's the output of 20 space heaters. See the problem? To pull off *really* fast charges like that, you can't really just look at what the individual cell tolerates. You have to quickly be able to dump the waste heat to a cooling fluid, which is an engineering problem, and you need cells that maintain very high efficiency during high-rate charge, which is a chemistry problem. Also at those sort of powers you have to even cool your wires, both on the charger and in the vehicle (an uncooled charger cable capable of delivering 1MW would be so heavy you couldn't lift it). Personally I think the high power charging standard should simply be set up suchly that the charger supplies the vehicle with coolant on a closed-loop cycle, so the vehicle doesn't have to haul around a massive cooling system, the vehicle would need little more than cooling ducts. But who knows how things will end up.
First off, why are you proposing both couple minute charges *and* swap? Swap is designed to be an alternative to fast charge. But as challenging as fast charge is, swap is even worse. These packs aren't little lead-acid starter batteries, they're many hundreds of pounds, upwards of half a ton or so, and form an integral part of the vehicle's structural integrity. And they're very valuable, too, people aren't going to want to get stuck with a crummy one. And even *if* the auto industry had a track record of collaborating on standards, which they absolutely don't, just the widely differing weight distrubution / form factor / power output requirements / capacity requirements / etc for different vehicles would demand each swapping station storing a massive range of different types of packs. All this ignoring the actual engineering challenges involved. It's just totally impractical. And I can tell you what's definitely NOT going to happen, a state trooper just walking up and swapping out something many times his own weight that makes up an integral portion of the vehicle.
Note, mind you, that the concept of getting a "jump" on an EV isn't a far-fetched idea, that is completely workable. You could even limp to the nearest farmhouse and slow-charge on regular wall power until you've got enough juice to make it to the nearest charging station. But swapping out the battery on the side of the road? That's like saying "replace your engine on the side of the road".
So the vehicle is supposed to have fast charge *and* swap *and* be a PHEV? Why on earth? You realize that each one of those things has its own major cost, maintenance, size, and mass associated with them? And thus consequently disadvantages all of the others?
The real problem is that they didn't standardize on high-power charging in the beginning. We got the SAE J1772 standard, but it tops out at 80 amps / 240V. Europe's a mess as it stands, with a bunch of competing connectors implementing IEC 62196-1, and again, no solid fast charging standard. This leaves everyone to have to pick and choose their own high-power coupler. It's idiotic, they should have standardized from the beginning, it's obvious that it's going to be a necessity for mainstreaming EVs. 20 minutes to charge your car while you take a lunch stop, fine. 3 hours to charge your car while you take a lunch stop, Not Fine(TM). Until you get fast charging standardized and available, the majority of consumers will continually hold that up as their excuse as to why they can't buy an EV (there's often some big holes in that logic, but that's neither here nor there).
There are a couple other possibilities for mainstreaming other than fast charging, but I don't see them around the corner. One is to have a whole day's worth of driving - or most of a day's worth (enough that if you charge during your meal / rest breaks, it's a full day) - on a single charge. In such a case, the upper end of J1772 is enough for all but very high consumption vehicles to charge you to full while you sleep, so you can drive another full day immediately after. But that requires multi-hundred kilowatt hour packs which would weight 1-2 tons and cost $50-100k with today's tech. It'll happen eventually, batteries double in energy density every 8 years or so (price drops happen too but they're more irregular and harder to predict) - but we're not to the point yet where this would be a viable option. The other option is making available self-steering genset trailers, like the AC Propulsion Long Ranger. It seems such an obvious stopgap - you've got a generator when you need it but don't have to drag it around when you don't, you could buy them, rent them, share them, etc. Your car uses gasoline on those occasional long trips but otherwise is pure electric with none of the problems of PHEVs. Unfortunately no major automakers are pursuing this approach (I'm not really sure why, the Long Ranger got good reviews). As it stands, the majority of manufacturers are pursuing some form of fast charging, but as mentioned, the standards situation is a mess right now. :
And then there's the issue of how fast charging changes incentives. As it stands, utilities *love* EVs because it lets them sell more power for rather little added infrastructure cost, they're largely stable nighttime loads. But once you start getting to 480V multi-hundred-amp daytime fast charges, it's just the opposite, that's horrible for them. It's possible to make them become once again something desirable for utilities by including a battery buffer inside the charger (trickle charges when not fast charging a car, then burst discharges), but I'm not aware of any fast chargers that come like that by default.
The other option is to accept that disadvantage of allowing fast charging EVs in exchange for having EVs smart grid integrated, so that all the cars left plugged in during the day charge when demand is low and stop charging or even reverse flow during those brief peaks. It's possible to incentivize EV owners as well - let them pick at what time their car needs to be fully charged, whether they want to allow reverse flow, etc. The more flexible they are about timing, the more their car can wait to buy power when it's cheapest, and they could get a rebate on reverse flow power sold at higher prices during peaks. Such a system would work well, leaving owners with the ability to choose the balance between speed and price (even potentially to earn a net profit on their car if they're flexible enough), and it'd leave utilities with a nice smooth generation/demand balance, much better than today. Unfortunately, neither the grid nor current EVs are to that point.
It *was* anti-soviet. That was its design purpose - to fight the soviets if they got into Europe. The only "evidence" trying to claim it was anything other than a group of anti-soviet cells who got out of hand in a couple countries was a bogus "army field manual" created by the KGB as a psy-ops. And if you have a better all-encompassing term than immoral, fine, substitute whatever word you want. I didn't want to just single out the bombings by the Italian right-wingers.
Is that a joke? The "gas deal" certainly provides cheap gas all right - so cheap that there's essentially zero profit in it for Gazprom. It's a real testament to how desperate Russia is to not look like they're dependent on the EU to buy their gas. Check out a map of Russian gas pipelines. Notice the complete lack of any pipelines anywhere near China's major cities. The gas deal leads from an undeveloped field through a nonexistent pipeline through nonexistent processing facilities. The pipeline isn't supposed to come online until 2020, and the main field until 2021. And that's assuming they can actually build it, which given their track record while *not* under sanctions is a big "If". And even if all that transpires, it's still a small fraction of their EU gas exports.
Anyone who actually looks at the "deal" can easily see it was just a PR move.
The concept that Russia can just turn east to China is beset by the fundamental problems that Russia doesn't have infrastructure connecting itself well with China, the vast majority of their people live nowhere near China, the vast majority of their industries are nowhere near China, and so forth. Russia is set up to function as part of Europe. And if it came down to it, does anyone in their right mind think that if the EU and US basically told China "us or them", they'd choose Russia, rather than the vastly larger markets of the US and EU that China's already intensely integrated with?
Not like the "breakup" with Russia would be painless for Europe. They'll be paying higher oil rates and significantly higher gas rates, plus higher rates for a wide variety of raw materials. But the situation is highly lopsided; Russia's GDP is an eighth the size of Europe's, a 16th the size of Europe + US. Whatever reduction in trade that hurts the EU / US hurts them an order of magnitude worse, barring huge multipliers on their part. Their manufacturing sector, in particularly high tech goods, is grossly undersized for the size of their population, and that's very unfortunate because such goods (in particular industrial goods, spare parts, etc) are often not fungible. They're also highly dependent on food imports (at least those are fungible).
Gladio had what to do with private corporations? It was an anti-soviet guerilla-prep program run by NATO in every country in Europe, wherein later a few groups got infiltrated by right-wingers who tried to use their power in immoral manners. But that doesn't stop a particlar brand of conspiracy theorist from crediting to Gladio everything under the sun.
Maglev trains are a whole different issue. You really can't go at those sort of speeds using wheels. It's hard enough to manage the sort of speeds that the Shinkansens go with wheels. Maglev is a great solution to the problem, in that it totally works and is quiet efficient. Not so great in that it costs the GDP of a small county for a couple dozen mile track, mind you.
I know I'd get jumped for saying it, but I think Hyperloop fits the typical use case for Maglev far better... ground-effect air cushion in a rarified atmosphere, and your track is just steel tubing on columns with a load-bearing requirement no greater than that of Disney's monorail.
It's hard to listen when, up until your last post, you weren't talking. "No, you're not understanding what I'm picturing" is not a criticism until you actually state what you're picturing.
It depends on the rate of heat flow. The act of compressing or decompressing 6x or more produces a great amount of heat. This flows into the walls of your container, trying to equalize with the ambient temperature.
Applying this to your tire example, we consider two reservoirs, one the tires and one an extra temporary storage tank. Since volume remains constant (isovolumetric process) and pressure increases 6x, under the ideal gas law temperature of the working gas increases 6x inside the temporary reservoir and decreases 6x inside the tires. Assuming no heat transfer, that's down to a chilly 50K in the tires and a burning 1800K in the cylinder. This, of course, doesn't happen in the real world, because with these temperature differentials with the outside world, you experience rapid heat flow to equalize with the surroundings. And there's no shortage of time for this equalization to occur (while you can insulate your gas reservoir, you can't practically insulate your tires). A typical acceleration or deceleration profile will be on the order of 10-20 seconds. How well do you think the gas inside the tires would remain at 50K over a 20 second interval versus rubber that's even hotter than ambient air? In practice, the heat from the air in the tires will almost completely equalize with its surroundings. As the temperatures equalize, the pressure rises in the tires and falls in the reservoir, depleting the pressure differential that the system is counting on to put the air back into the tires.
Now, I would be curious as to your counter to this, except...
Let me know when you decide to stop being an asshole when discussing things on the net.
In no manner does that reduce visibility. I can't even envision how you're imagining that that reduces visibility. Some car dashes are level, some slope up, some slope down, this isn't at all radical. You have your dash begin below the windshield and intercept it at an upwards angle, just like is done in thousands of cars already.
No, in general, the strongest shape for a building for a given amount of material is an arch in the 2 dimensional case, a vault in the 3 dimensional case. For overall loadbearing of an evenly-spread load, the strongest shape (in terms of minimizing bending forces) is a parabolic dome, which reduces bending stresses to zero and maintains a purely compressive load, which is generally much easier to withstand. Modern buildings use straight lines to minimize their footprints, not because they're stronger. Seriously, have you ever looked at the shapes people had to use to build large buildings before the advent of modern materials? Hint: they're not big boxes.
The more your interior structure is solid - aka, if you have an internal skeleton - the less important an arched / vaulted structure is, as you have a more even distribution of lateral forces. On the other hand, if you have a large interior space supported entirely by its exterior, it's very hard *not* to use large arches / vaults, even when dealing with modern building materials (think it's a coincidence that very large enclosed sports stadiums are domed?). And guess what? Cars are a large interior space supported entirely by its exterior, using as little material as you can get away with.
Are you talking about two pressurized or unpressurized balloons where you're creating a tiny pressure differential between them? Because it's the act of increasing the pressure that's the highly lossy process. And your ballons are never going to flow from low pressure to high.
How about instead of dancing around the topic, if you think I'm misunderstanding what you're envisioning, you actually describe in detail what you're envisioning? I'm just simply telling you, if you're compressing a gas, it doesn't matter if you're recovering or storing energy during the decompression, the compression itself is highly lossy. You can recover 100% of the stored energy of the compressed air and it still leaves you with major energy losses.
Describe how you're getting the tires back up to 120+ psi.
You angle the dash up to the windshield. Nobody says the dash has to meet the windshield at the same angle the windshield is raked at.
My rear window on my Insight is even more raked than the optimal front window on a streamliner, there's no distortion.
How on earth are you coming up with that one? The elongated egg-shape of the front end of a streamliner is one of the strongest shapes in nature, and the A-pillars follow the shape. The Aptera 2e had a 4,5x higher roof crush strength than the federal car mandate - a much more impressive figure than their door crush strength, which was only about 2x the federal car mandate.
No, it simply is lossy, period. Air compressors are geneally at 10-20% efficienct, usually under 15% for small one. To get any sort of significant improvement on that you have to add in one or more bulky waste heat recovery cycles (yes, thermal engines), which are limited by Carnot's law, which dramatically limits your recovery potential.
It's not "confirmation bias", it's a fact; air compression is a highly lossy process. If you don't believe me, ask anyone else who has experience with compressors. Or just google it.
I'm sorry if you don't like the fact that your proposed solution is vastly inefficient. But it IS vastly inefficient.
Oh, forgot to mention - Aptera 2e's drag coefficient was 0,15. It could cruise at a steady 55mph on 80Wh/mi, a bit more than the power of two blow driers.
Well, one of the most extreme examples was the "car" I was on the waiting list for, Aptera's 2e, which was about 2 months away (I have their old internal corporate schedules and checklists) from shipping to customers when the board brought in Paul Wilbur to manage the company. Wilbur is a Detroit car exec who had ran one company into the ground after the next; the first thing he did after taking over the company was order a redesign nearly the whole vehicle trying to "mainstream it". The changes ruined the vehicle and he burned through all the company's money in short order (including taking a large salary for himself), bankrupting it. Yes, I'm still bitter over that.
( And yes, I fully realize that I vehicle *that* streamlined isn't for everyone ;) )
For cars that have shipped in some degree of volume, the EV1 really stands out. While both with less interior room and higher drag than the Aptera Mk1, it still sported an impressive 0,19 drag coefficient and 0,36m^2 frontal area. About 1500 were made. Another low volume but from way back was the Tatra 77, with a drag coefficient of 0.212. Not bad for 1935! The Mercedes CLA has a drag coefficient of 0,22; I'm not sure of the volume. The Tesla Model S's drag coefficient is 0,24; it's new but they've already delivered tens of thousands. The first-gen insight (what I drive) was 0,25; there were 17k sold. However, also at 0,25 are the Sonata Hybrid, the Audi A2, the Lexus LS 430, the Pugeot 508, and the Toyota Prius. So all together you've got millions of those.
Now, a lot of those aren't low in frontal area, just drag coefficient. But frontal area is something that also provides benefits (interior room); a high drag coefficient doesn't provide benefits, so reducing that figure matters the most.
The EV1 was indisputably both the most advanced and most popular electric offering at the time, and most critically, they basically gutted all similar research and sold off their patents, not even pursuing hybrids. Their selling off of the patent rights also made it impossible for several other companies to have continued their EVs even if they had wanted to. GM was also the most active and public of companies trying to kill off the ZEV mandate. So all together, it's not surprising that they earned the lion's share of the puiblic scorn on that one. The next most popular of the ZEV-mandate EVs, the RAV4 EV, wasn't taken away from its owners, and for a decade the few that remained were the best EVs available on the market and commanded ridiculous prices relative to their age and hardware specs. The Ford Ranger EV was pretty primitive, and they too were willing to sell to owners.
The EV1 really was an amazingly advance vehicle for its age. It was one of the first aluminum-framed production cars from a major automaker. It had a then-recod low drag coefficient of 0,19 *and* a very low cross-section, something aero-lovers like me adore. It was so streamlined that a prototype that GM re-geared but otherwise used the same chassis and drivetrain hit 183 mph. The drivetrain was miles ahead of its competitors, a highly efficient AC inductive motor that could handle both accel and charging from the same system; the drivetrain of the Tesla Roadster is a direct descendant (Impact -> EV1 -> tzero -> Roadster). The EV1 had all sorts of features that are now common but were rare or unique at the time, including a control computer that could be programmed to do scheduled tasks, for example, to preheat/cool the vehicle at a scheduled interval. Speaking of climate control, the EV1's was more advanced than that of most EVs today, using a bidirectional heat pump for both heating and cooling along with waste heat recovery, with heat augmented by a resistive heater.
While it was out there, GM wanted the public quiet involved with the EV1. They plugged it in ads, using it as a "look at us, we're high tech" vehicle. But they never wanted to have to build it in the first place, and they seriously bungled the PR during the termination. When the guy who ordered its termination called it his biggest mistake, the guy who presided over GM during its march to bankruptcy, that's a major statement.
I'm not talking about a long hood so much as a tall hood relative to the rest of the vehicle - the car starts, then suddenly it's nearly as tall as the roof. Example: here's the concept mode for the Chevy Volt. I took one look at it and smacked my head, anyone who knows aerodynamics can see that that thing is going to have the aerodynamics of a rolling brick (spoiler: that's a whopping 0,43 drag coefficient on a supposedly "efficient" car!). Nobody should have been the least bit surprised when it changed dramatically going from concept to production. Yet that concept look is supposed to mimic the look of a "chopped" car (despite not reducing the frontal profile) and thus be "sexy", "muscular-looking" and desireable. It just ruins it for me. I know that I'm weird in being turned off from a car by seeing its awful aerodynamics.
Basically, there's no reason that your "long hood" has to quickly flare to full width/height in the front, then remain relatively constant height up to the windshield. That's highly suboptimal for aerodynamics and achieves nothing in terms of giving you a long distance to decelerate in. The optimal aerodynamic front end is roughly elongated-egg shaped.
Beyond that, you don't need a long hood at all, either, for crash protection, just a long deceleration distance. Hood length and deceleration distance, though related, are not equivalent. One factor, for example, is where the driver / passenger are located inside the vehicle. If you have a highly raked windshield (optimal aerodynamics) then the driver and passenger have to be located a bit further back from the front of the car for headroom reasons, so there's still plenty of room ahead of them to the foremost point on the vehicle. Also at play is how the vehicle deflects force in an accident - whether it crumples straight back or whether the nose rides up during a collision (the latter gives extra deceleration distance). A greater rake on the windshield also decreases the chance of windshield penetration.
It should also be pointed out that such a design also enhances pedestrian safety in a number of respects. The lack of an abrupt flare means a pedestrian is more likely to be hit at an angle and accelerated over a greater length of time (reduced G-forces). The matching rake between the hood and windshield additionally means they're not going to suddenly decelerate at the windshield. To be fair, of course, some pedestrial-safety features, such as low bumpers, run counter to aerodynamics.
As for that SkyTran PRT: Judging from the image on the cover, it looks like a reasonably good shape up front, but the rear end sucks. Contrary to popular misconception, it is *not* good to have a rounded rear end. Once your angle gets too steep, the flow will detach from your vehicle, leaving a low pressure wake. You want to not exceed the critical angle (aka, use a roughly constant taper angle) and prolong the detachment as long as you can (aka, as gentle of a taper as your design parameters allow), and when you can't delay the detachment any more, you want a relatively abrupt cutoff, potentially with a vortex generator to draw down the stream. The actual details vary depending on the situation, and one always needs to do CFD work, but that's a rough "in general" for aerodynamic optimization
Update: I searched more and found some rather different looking PRT images. These are of an excellent aerodynamic form, with an appropriate taper in back (though I personally prefer a vertical taper to a horizontal taper for cars... theirs makes sense for their particular application, however). I'd be willing to wager that their cover image was an early artistic concept, while the latter was something they actually did CFD work on.
It could be (though that would have engineering challenges of its own, and not just noise minimization), but remember that compressing air is a rather lossy process. If you're rapidly dropping the pressure, say from 120psi to 20psi then back, every time you need traction, you're going to lose an awful lot of energy doing so.
Given that increased camber is often a good thing when cornering, and that there's no inherent physical loss mechanism in changing camber, and your required hardware to do so isn't particularly onerous, that's why I mentioned that particular possibility. But overall, that was just an example; the key point is, there's an order of magnitude difference in rolling coefficients between today's car tires and that of rigid wheels**. If you can get rid of all of the compression/flex in your general-use case, and only add it in when you need the additional traction, and make use of a vibration isolation or active cancellation system to maintain ride quality, you could virtually take rolling losses out of the picture.
** - I should clarify that when I say "rigid wheels" perform an order of magnitude better, I don't simply mean "anything non-pneumatic", but rigid to the degree of train wheels or ball bearings. For example, in wheelchairs, pneumatic tires often actually have *lower* rolling losses than "rigid" wheelchair wheels; the latter flex too much and thus lose more energy in the process than their pneumatic equivalents. It's not the use of air that's the problem, it's the repeated bending of material, turning your kinetic energy to heat. To achieve dramatic improvements in rolling coefficients over conventional tires, a rigid wheel needs to offer dramatically less flexure than its equivalent tire as it rotates. But it also has to be lightweight to minimize total mass and in particular unsprung mass. Hence the suggestion of carbon fiber / foam core wheels; I would expect such wheels to be able to meet that kind of spec if built well enough. But who knows without experimentation...
It's also a fair criticism that once you start going for such extreme rolling drag reductions, imperfections in your road surface are going to have an increasingly large impact on your achieved rolling coefficient.
Oh, and just an additional comment, from my past experience in the auto industry: this wasn't an "oops, I wasn't supposed to say that!" remark. The Japanese companies are in general very good at controlling information flow; this was clearly planned for him to say that. But the reason he said it was almost certainly not to prepare people for the coming day of flying cars; it's about perception. It's a major brand positive for an auto maker to be perceived as high tech / cutting edge / innovative, and they want to culture that.
Remember Rick Wagoner, the guy whose tenure at GM made a graph of the company's stock look like a double diamond ski slope? Of all of the things that he could have regretted, he's stated that the number one thing he regrets was axing the EV1 (late 90s electric car) program. The EV1 lost tens of thousands of dollars per unit and there weren't many made so there was major overhead on top of it; but by axing the program to save a little money, they willingly gave up the perception of being a tech innovator, right at the time the Japanese companies were introducing hybrids. Even to people who weren't considering buying a Prius or Insight - aka, the vast majority of consumers - the very perception that Toyota and Honda appeared to be high-tech innovators demonstrably influenced consumer buying decisions.
Car makers have slick PR teams who survey and carefully try to manipulate the public perceptions about themselves to influence buyer behavior. Expect that the decision to mention this came straight from one of them.
Sort of.
First off, in general to get up to 95%, you're talking "racing supercars" territory. But honestly, not even that (see below).
Secondly, the aero and rolling drag equations (in particular, rolling) are just approximations, along the lines of "assume a spherical cow". The real-world deviation from the formulas is usually described as changing drag coefficients under different conditions, but in the case of rolling drag, it changes so much at high speeds due to increasing magnitude standing waves on the tires (greater rubber flex) that it's better to add into the modeling a nonlinear component; it's not at all accurate to say that it's "pretty much constant". If you don't at least use a piecewise formula for the rolling coefficient in your vehicle energy consumption calculations, you get results that are way off.
In practice, even at supercar speeds, you'll never get up to that mythical 95% aero drag. Rolling drag is also greatly affected by a number of other properties besides velocity, including road surface, tire pressure, tire temperature (rolling resistance drops as you drive as the internal pressure rises), and road condition (contrary to popular myth, in light rain conditions, the main increase in rolling drag is due to tire cooling, not due to pushing water out of the way).
Oh, and I've neglected to mention thusfar parasitic / operating losses as another vehicle energy loss mechanism, which also play a role (usually small, but sadly growing), which makes it even harder to have aero be such an overwhelming percentage of the picture as was previously claimed. (there's also braking losses, but they're primarily an in-town thing)
My presumption is that they're still using wheels for acceleration. For example, in a front-wheel drive car, you could hover the back wheels, at least until you need traction from them (for example, turning). With a pulse and glide configuration, you could even hover the drive wheels for a good chunk of the time.
Still, I think there's much better options for reducing rolling drag.
That's not true. It varies from vehicle to vehicle and between driving profiles, but it's usually 50-75% of the resistance at highway speed coming from aero drag - not 95%. Rolling drag remains a significant loss factor at all speeds.
That said, this doesn't sound to me like the most logical approach to tackle rolling drag - wheels are more efficient than hover as-is in most general-use cases, and I can easily envision a lot more that could be done. For example, you could use very high pressure (120+ psi) tires with a hard, thin central tread, relying on automatic camber to a thick, sticky side tread during accel, braking, cornering, or when traction control kicks in (the additional vibrational load from cruising on high PSI tires could be canceled with, for example, a cable vibration isolation system or active vibration cancellation). Such a system should be able to approach the rolling coefficients of hard steel wheels (a tenth that of traditional car pneumatic tires - effectively rendering rolling losses irrelevant). Heck, if you're going to that extent, it's not much further to go all the way to completely solid wheels (though you'd want foam-core carbon fiber or similar to keep the weight and in particular unsprung mass down, not solid steel) and not even have to deal with tire inflation or puncture risk. So long as you have a way to automatically shift to a thick, sticky tread as needed based on current traction conditions and have a mechanism to soak up the higher vibrational loads to maintain ride quality, you're fine.
Is that a pretty huge deviation from standard practice? Yeah, by no small amount, it's literally reinventing the wheel. But you know what, it's also a pretty huge deviation to have cars outright hover on the highway. ;)
But yeah, you're right in that rolling losses aren't the *primary* loss mechanism on the highway. A lot more has to be done to tackle aero drag, and that's trickier - not least of which because the optimal shape varies based on speed and things like crosswinds (and the more you optimize your shape, the bigger of an issue this becomes). One of the more clever ideas I've seen - I don't know how it'd play out in the real world, mind you - was Aptera's plan to take a page from Gerald Bull's playbook and fill in the low pressure wake with air ducted in through the cabin. There's also a fair bit of research designed for aircraft (where aero drag is an even bigger issue) that could translate to cars, for example, skin textures or microstructures designed to maintain laminar flow or reduce surface drag. One of the more exotic variants of that which I've seen is a taut film outer-layer over a microscopic layer. The film vibrates in the wind between its ridges, setting up standing waves which separate the laminar flow from the surface, reducing the flow speed in contact with the surface and thus reducing direct surface drag. There've been peer-reviewed papers on it, and one of the researchers founded a company that now makes kits to reskin a variety of small aircraft (not very many thusfar, the skin has to be custom designed for each model). That's of course just one example among many, it's a very active field of research, as even a fraction of a percent reduced aero drag on a commercial airplane results in massive fuel savings.
Honestly, I'll be happy if we can just get people's style preferences to shift away from naturally high-drag forms like those ridiculous oversized front-end things where you can barely see over the hood. I know I'm out of the mainstream, but I love the look of aerodyamics. Real aerodynamics, not counterproductive curvy features that a lot of people think are "aerodynamic" but actually raise your drag. I want my car to look like a wingless plane, a car that cuts through the air like a knife rather than a clobbering oaf shoving it all around as it drives by ("Excuse me air, coming through, excuse me, sorry there!"). I want a rounded front end and a rear end that tapers vertically down with as long of a t