Modern turbofans have over 40% thermal efficiency. True, there are some additional inefficiencies associated with transforming shaft power into thrust - but since a turbofan and an electric ducted fan both use the same basic means of generating thrust, I see no reason to believe that an electric engine would do much better in that respect. (Also, when people quote wonderful-sounding efficiency numbers for electric motors like 95%, they are ignoring other large inefficiencies in the system, like battery internal resistance, voltage conversion and power filtering.)
Are you sure about that 1GWh figure?
Boeing 777-200LR fuel capacity = [180 kL]
Energy density of Kerosene = [37 MJ/L]
Energy content of a full tank = [180 kL] * [37 MJ/L] = [6.7 TJ] = [1.9 GWh]
Assuming the turbofan has [40% thermal efficiency], and the electric plane has [80% battery-to-shaft-power efficiency], this means the equivalent battery-powered plane will require about [1 GWh]. I am fairly confident this is accurate to the one significant digit at which I listed it.
As a sanity check, consider:
The turbines, of which the 777 caries two, have a naval equivalent which produce up to [40 MW shaft power] each.
The plane can fly for around [17600 km (max range)] / [892 km/h (cruise speed)] = [19 h] before refuelling.
Given [1.9 GWh] in the tank, flying for [19h] implies an average energy consumption rate of [100 MW]. [100 MW] * [40% (thermal efficiency)] = [40 MW shaft power], meaning that at cruise the engines are producing about [50% of max power] (which is not necessarily the same as being set at [50% of max throttle]).
Regardless, my basic point about the difficulties of charging stands even if I am off by quite a bit concerning the relative efficiency of kerosene turbofans versus battery-powered ducted fans.
Human-carrying solar planes are unlikely to replace something like the Cessna 188, because there simply is not enough space in community airports for everyone to have their own 200 foot wingspan single-person solar slow-poke, even if that's what people wanted.
As to "small efficient electric light aircraft" - I already said that electric aircraft are plausible; they just won't be powered by solar panels while in flight.
I agree that (thin-film) solar is worth considering more seriously for a slow, buoyancy-lofted craft like a Zeppelin - but those would have to target a different market than something like a 747, because of their low speed and sun-blotting size. For now surveillance-like tasks, and maybe cargo transport to remote areas seem like the only good fits.
As you say, rising fuel prices could open up other possibilities later - I doubt large-scale, long-range passenger transport will ever be one of them, though. People are kind of the ultimate "time sensitive" cargo.
You would need these batteries to charge very fast while on the ground, have long life-spans and cycle-count ratings for it to be economically worth it.
No, you don't need fast charging rates. With an airport, you have dedicated ground crews handling the preparation of the planes between flights, employed by the airline. So instead of refueling the plane, they just need to swap out some battery packs while the people are unloading. It should be entirely possible to build a fast-swap battery module into the underside of the fuselage, or thinner modules into the wings.
A battery-powered Boeing 777 equivalent would need (very roughly) 1 GWh in its battery pack. Someone recently claimed that Tesla is paying something like $200/KWh to build their battery packs now, which implies that a 1 GWh pack would cost around 200 million dollars. Even allowing for advances in technology (which are, of course, required in order to make such a battery light enough to fly in the first place), it would surely still be worth 10s of millions.
Such prices are not unreasonable considering the cost of the airplane itself - if only one or two packs are required per plane. However, even with battery swaps, you still need to be able to charge the pack in something like the same amount of time it takes to discharge it in flight: about 10 hours. Otherwise, you end up needing way too many spare batteries and charging stations.
For a 1 GWh pack, this means routinely charging it at about 100 MW. If that's not a "fast charging rate", I don't know what is. Sure, on a per cell basis 1/10th C isn't that much - but the sheer size of the thing is going to cause real difficulties for safety, cooling, etc.
Each large airport would require hundreds of chargers (every one equivalent in size and cost to a very large electrical substation) and a local generation capacity greater than most nation-states. The land-use alone would be prohibitively expensive, when you consider that large airports are usually found near city centres with astronomical property values.
Batteries, or solar cells, don't make thrust by themselves either. You'd still need the same turbofans, just with heavy electrical windings in the middle rather hollow combustion cavities. Electric motors tend to be quite a bit heavier than empty cavities are, so I'd expect the electric engine to be probably a bit heavier.
Of those parts, I believe that most of the weight, complexity, and expense is associated with #2 and #4.
In a hypothetical electric airplane #5 (the nozzle) is not needed, and #4 (the turbine) is replaced by the electric motor. It is not obvious to me which of those is heavier or more expensive, in the long run.
One might expect that #2 (the compressor) and #3 (the combustor) would go away also, but in reality they are still required, albeit in a very different form. Why? Because currently the only plausible way that an electric airplane could compete in range with a hydrocarbon turbofan design, is by powering itself with either metal-air batteries, or fuel cells. In either case, a great deal of air must continually be collected, compressed (not as much as in the turbofan, though), and "burned" (but at much lower temperatures than in the turbofan) inside the power source.
The compressor will get much lighter and cheaper, but still be required. I don't know if the reaction chambers and catalysts for the electric design end up being lighter or heavier than the combustor - but they will certainly be more expensive, if we go by current fuel cell prices...
Perhaps jets are wasteful and electric motor planes are less wasteful? I would guess so but don't know how to derate that.
Modern jet engines are very efficient (over 40%), assuming you spend most of the flight near their intended cruising speed. Electric might do better - but not more than 2x better, and probably less than that.
Thus in raw numbers that 10^10 could power 350 aircraft. Since batteries have loses assume 75% of that is more practical. Still that's more than the number of aircraft taking off per hour.
You forgot to divide the solar capacity by three to account for night time, intermittent clouds and fog, and the lesser amount of light available early in the morning and late in the afternoon.
Obviously I ignored that takeoffs use a lot of fuel. But that's factors of 2
The 750 average gallons per hour number you used is reasonable for a 737, even allowing for takeoffs (which are somewhat balanced out by the low-power glide into landing). However, many jet planes are a great deal larger than the 737; for example, a 777 or 747-8I burns about 5x as much fuel.
jet fuel is about 42MJ/kg. the current best flow battery is about 5MJ/kg. But recent advances suggest this could rise 10 fold in the near future.
Do you have a source for this?
I find it very difficult to believe that any battery design which stores its own oxidizer can ever compete with a hydrocarbon for "energy density", since the hydrocarbons get to cheat by not counting the majority of the mass required to complete the reaction (at least 3x as much oxygen is required, as fuel). My expectation is that the only kinds of chemical batteries which could even theoretically compete with hydrocarbon fuels, would be metal-air batteries since they get to cheat in the same way.
A solar-powered direct replacement for something like a Boeing 747 is impossible, period. Incremental technological development cannot get us from here to there.
Boeing 747-8I maximum fuel = [240 kL]
Energy density of Kerosene = [37 MJ / L]
Thermal efficiency of a modern turbofan engine = [40+%]
Flight duration = [16+ hours]
So, even a hypothetical 100% efficient solar-powered 747-8I replacement would require about 62MW of average (not peak!) power to operate. The maximum power that can be collected by a solar energy system (no matter how efficient) is limited by its surface area: it cannot gather more energy than what is present in the sunlight hitting it.
Maximum solar irradiance at Earth's Orbit: [less than 1.4 kW/m^2]
Upper surface area of a Boeing 747-8I: [less than 1000 m^2]
Maximum solar power available to a solar 747-sized object: [less than 1.4 kW/m^2] * [less than 1000 m^2] = [less than 1.4 MW]
Even an ultra-high-tech solar 747-8I replacement could not possibly generate more than about 2% of the power required to perform the same mission. It would inevitably need to fly much slower and lower (probably low enough for cloud shadowing to cause major problems), and/or carry a far smaller payload.
Barring a major (read: not foreseeable) physics or engineering breakthrough, true solar-powered jet replacements are not possible. Electric planes might happen eventually, but they will require refuelling or recharging on the ground, just like today's hydrocarbon-powered designs.
He's lucky he didn't go blind while making this. That fireworks clip, in particular, was just asking to get hit in the face with something burning and white-hot.
There *is* still such a thing as secure communications, you know.
For practical purposes - there really isn't for the average man on the street (in the West, at least).
Businesses (whether employers, vendors, or service providers) generally use some combination of phone, fax, email, and snail mail. All of those systems are thoroughly compromised. Email could theoretically be semi-secure - but that would require both ends of the conversation to be using computers that didn't rely upon millions of lines of poorly-vetted and/or proprietary code to function.
As for friends and family - many of mine are simply not tech-savvy enough to correctly use and maintain a "secure" computer communications set-up, even if I taught them how.
If you really think that the general public is capable of keeping their electronic communications private from the NSA using present-day civilian tech, you are either living in a fantasy world, or have a poor grasp of how computer security (and probably computers in general) actually work.
You don't have to use Skype, specifically - but the phone system, email (and snail mail, for that matter), Facebook, Google Hangouts, and pretty much any other modern communication system you could name all have the same problem.
And yes - refusing to call, text, or (e)mail people is a pretty good way to make yourself into a friendless (and likely jobless) recluse.
As far as I can tell based on the leaks from Snowden, and my own rather deep understanding of how modern computers work, the NSA is pretty much going to spy on me, my friends, and everyone on the internet regardless of whether I use Skype or not. Moreover, the main practical alternative to Skype in my life, is my cellphone which is no better as far as spying goes.
I am not "tolerating" the trampling of our rights; I simply do not see a meaningful technological alternative short of becoming a Luddite or a friendless recluse.
(I do not believe that Tor, encrypted email, etc. would actually be secure for my day-to-day communications, in practice. Too many other layers of the technology stack - the web browser, the operating system, the firmware, and my internet service - are readily compromised in ways that I cannot really do anything about. The "anonymity" provided by Tor would be easily pierced if I just used it to talk to all the same people that I know in real life.)
And why? Just so you can get laid? Lame.
Get your mind out of the gutter. People are not just sex objects, and I'm not interested in a long-distance relationship (the only kind that might require Skype), anyway.
I know it's hard to believe, but some of us Linux users do actually have friends, family, or business contacts who are members of the other 80+% of the population that uses Windows. My social life is a higher priority than tinfoil-hattery, even though I am not happy about the NSA spying on everything and everyone "just in case".
You left out #4: The errors in spelling or grammar are actually bad enough to obscure the meaning of the message.
Attempting to correct or clarify the message in such cases helps keep the present conversation from derailing due to misunderstandings; it's not just about training people to do better in the future.
Having said that, true examples of #4 are rare, unless the writer is either not a native English speaker, or is just being very lazy (as is common when texting). The writer himself is not in a good position to judge how confusing his own mistake really is, though, so people really ought to err on the side of just accepting the clarification, instead of calling anyone who finds poor spelling and grammar confusing a stuck-up jerk.
That Prius only reaches that very good efficiency as the engine can run at optimal load and optimal RPM all the time, running the generator, charging the batteries.
The 38.5% number is a measure of the peak thermodynamic efficiency of the engine alone; it says nothing about the usage patterns of the engine in the Prius.
A regular car or motorbike most of the time is either idling (0% efficiency) or running at sub-optimal loads and RPMs, both quickly lowering overall efficiency.
This is a good point. In theory, something like the Chevrolet Volt may be the best near-term solution, as it has a big enough battery to allow the engine to run almost exclusively at the optimal load, while still having good range like a regular ICE vehicle. Make it a plug-in hybrid if the grid in the area is decent (i.e., not India).
Many vehicles in India use two-stroke engines and are poorly maintained. A total efficiency as low as 10% for those vehicles may very well be a realistic number.
True. On the other hand, India has a really terrible electric grid too (30% losses, not 10%), and little money with which to fix the grid, buy modern four-stroke ICE vehicles, or buy cutting-edge electric vehicles (the only kind which can compete range-wise with an ICE currently). So anything they do is probably going to fall short of Western performance standards; trying to figure out which option falls least short is an interesting problem.
I never said our republic is healthy (we all know it's not)... just that demanding Congress make their decisions based on what might be the indirectly implied "will of the People" via the presidential election is not reasonable. Many of the ways in which America's political system is dysfunctional affect the office of President just as much as they affect Congress.
The ball gains momentum from the train in an elastic collision. The train loses momentum.
Or in other words: in the second question the ball is faster than in the first question and the train is slower.
Let [mA] be the mass of the smaller object.
Let [mB] be the mass of the larger object.
Let [vA0] and [vB0] be the pre-collision velocities of the two objects.
Let [vA1] and [vB1] be the post-collision velocities of the two objects.
Let [AB] = [mA] / [mB], which is the ratio of the lesser mass to the greater.
With a little algebra: [mB] = [mA] / [AB]
By the law of conservation of momentum: [mA]*[vA0] + [mB]*[vB0] = [mA]*[vA1] + [mB]*[vB1]
By substitution: [mA]*[vA0] + ([mA] / [AB])*[vB0] = [mA]*[vA1] + ([mA] / [AB])*[vB1]
By subtraction: [mA]*[vA0] - [mA]*[vA1] = ([mA] / [AB])*[vB1] - ([mA] / [AB])*[vB0]
By division: [vB1] - [vB0] = ([mA]*[vA0] - [mA]*[vA1]) / ([mA] / [AB])
Simplified: [vB1] - [vB0] = [AB]*([vA0] - [vA1])
Let [dvB] = [vB1] - [vB0] and [dvA] = [vA1] - [vA0]
By substitution: [dvB] = -[AB]*[dvA]
By division: [dvB] / [dvA] = -[AB]
From the above, we can see that the ratio of change in velocity for the train versus the ball, or the spacecraft versus the planet, is equal to the (negated) ratio of the smaller mass to the greater mass:
A large train weighs in excess of 10^6 kg. A tennis ball weighs less than 0.06 kg. Thus:
So technically, yes the train slows down - by an immeasurably small amount that is completely irrelevant for any purpose other than ensuring conservation of momentum. #1 takes a mere 0.45 seconds, but #2 also needs an extra 54 nanoseconds.
I would approve your answer here as pedantically correct... except that the application you have attempted to make of it to gravity assists is just dead wrong:
x-dV seconds
That's obviously invalid, and not helpful at all. x and dV are specified in different types of units (time versus speed), so one cannot be directly subtracted from the other like that. Repeating the math from above, but now for the gravity assist case:
A truly gigantic manned spacecraft (required for such a long journey) might weigh 10^7 kilograms, while an ice giant like the theorized "Planet Nine" might weigh 10^26 kg (like Neptune). The maximum plausible velocity change for the spacecraft from the gravity assist would be around 4 km/s.
Now that we know roughly how much "Planet Nine" could be slowed down by an encounter with our spaceship, we can calculate how much faster the ship will escape the planet's gravity well as a result. We'll use Neptune's Hill Sphere radius as a reasonable (and lazy) approximation for the size of the well.
[ship speed] = [2 km/s] Note: As in the train case, from the planet's frame of reference, the ship does not (in net) speed up; it only changes direction. [planet dV] = [-4*10^-19 km/s] [Hill radius] = [1.16*10^8 km]
The above formula is grossly oversimplified (since, unlike an actual elastic collision, this acceleration is far from instantaneous) - but should nevertheless
The point I'm trying to make, though, is 'if somebody doesn't vote, how do you determine their intention?' Answer me that. You say you didn't vote. So how is Congress, or the President, supposed to divine how you feel on, say, health care?
As I said to someone else in this thread, I think Congress should simply vote according to their own consciences, instead of trying to indirectly infer what a referendum on each issue would show. That's how a republic is supposed to work: you vote for someone you trust to make good decisions, and then let them do their job (or vote them out).
As to my own intention - the desires of my demographic are not unknown to Congress or the President; there just aren't enough people in the United States who truly share my views to form a politically relevant voting block (and we're not into bribery, either). The Government knows what we think; they just don't care, and never will unless the demographics change.
I would be a lot more likely to directly participate in the electoral process if America's voting system wasn't designed in such a way as to effectively disenfranchise anyone who can't at least come close to assembling a majority.
I do vote on referendum or ballot measure type stuff, because in such Yes/No contests my opinion actually appears on the ballot, unlike in the presidential Red vs. Blue vs. [Redacted] contest.
No it is not. Most of the stuff involved is 99% efficient, so I simply averaged it to 90%.
Sources? Here are mine:
1) In the USA, transmission and distribution losses are estimated at 6% by the EIA. However, India (the subject of the original post) has really bad infrastructure, in comparison. Their losses are estimated at about 30% by the World Energy Council. So, I was actually way too generous when I said "90% efficient" for this part.
2) The Tesla Roadster is said to have a battery pack charge/discharge efficiency of 86% in an article from Stanford University, which claims to be drawing from a source published by Tesla itself.
3) The National Electrical Manufacturers Association requires a minimum efficiency of about 92% for some large induction motors. However, I found an answer on the Electrical Engineering Stack Exchange site indicating that Tesla uses a slightly less efficient type of motor, and also that a ~97% efficient power controller is required, which brings the real efficiency down to ~88%.
Using the exact numbers I sourced, above: 88% of 86% of 70% of 42% = 22%, which is even worse for a coal-powered electric car than what I originally posted (because I was intentionally rounding up a bit to allow for future improvements).
That link about the Prius Engine is nice! However keep in mind: that would require all new cars to use engines like this. Which they hopefully do in not to distant future.
The extremely aggressive CAFE standards recently set by the Obama administration are already pushing things hard in that direction in the USA. Admittedly, India probably won't be buying many ICE cars produced for the US market in the next decade - but then, they won't be buying fancy electrics like a Tesla, either.
Interesting, but still, if you numbers are correct, this only applies to a Prius, which is a hybrid (half electric) which represents a very small percentage of all cars on the road,
The 38.5% efficiency is for its internal combustion engine alone; the fact that the Prius joins that engine to a hybrid-electric drivetrain does not effect that number.
and there are not that many cars with such efficiency either.
I picked the Prius simply because it's the easiest thing to find precise numbers for. However, a little poking around on the web suggests that a more typical current generation gasoline engine might be 30% efficient - which is still neck-and-neck with coal-powered electrics. Diesel engines are much better, at 40+% efficient.
You are also not considering the PRODUCTION and TRANSPORTATION of fuels, which also amount for a large % in reduction of energy.
angel'o'sphere left a lot of things out of his original ad-hoc analysis; I followed suit in the interest of making an apples-to-apples comparison. A more complete analysis would consider:
1) The efficiency of producing and transporting fuels - including the coal which ultimately powers the electric car in angel'o'sphere's original comparison, not just the gasoline or diesel for ICE cars.
2) Mechanical inefficiencies in the drivetrain of both electric and ICE cars - this will favour the electrics on average, since they usually don't need such an elaborate transmission.
3) The greatly reduced weight of ICE cars compared to comparable electrics (batteries are very heavy), which means that less energy is required to accelerate an ICE car in the first place.
...And a million other economic, environmental, and logistical factors, too, because energy efficiency isn't the be-all-end-all measure of technological, economic, or environmental superiority.
As awareness for health and the environment grows, and given that all ICEs produce fumes toxic for humans, I can predict there will be a law in the future PROHIBITING them all.
You do realize that the point of comparison in this discussion is COAL POWER, right?
I highly doubt that we will see a blanket ban on gasoline (or event diesel) internal combustion engines prior to a ban on burning coal. While it is possible (given enough money) to prevent "toxic" emissions from any hydrocarbon fuel, it is far harder to do so for coal than gasoline, ethanol, or natural gas.
All of the aneutronic fusion reactions you point out have a difficulty...
Interesting. I had heard about that issue for proton-boron, but was not aware that it applies to Helium-3 as well.
All that said, it'd be awesome if someone conquers the difficulties and makes either sort of direct conversion nuclear practical. I even support using tax funds to research toward those goals. But I see them as long shots...
I don't know that I would call direct conversion nuclear power (collectively) a "long shot", but certainly there is little reason to expect cheap net power from any of these schemes in the near term.
I did find the early Pollywell experimental results revealed by Jaeyoung Park's recently rather exciting, though. Of course, even if it gets fully funded and turns out to be fundamentally workable, that's still probably at least 15 years away from a commercial product.
and in the meantime, the market is going to vote with its dollars and go with what works today and is cheap!
Most of major the Generation IV fission designs have been proven workable, and I think some could be cheap enough - if the regulatory and political environment actually allowed them to be built in the West. But instead, we'll probably just keep extending the life of the existing decrepit Generation II installations, with their dubious safety and economic record...
Another huge advantage is the fuel and waste is not in the primary coolant. Having your primary heat exchanges being totally radioactive makes maintenance hugely expensive since its needs to be more or less 100% remote. the Machines are coming, but not quite yet.
This is especially true when you consider that high radiation environments are pretty hard on electronics, as well as people. Any electronics which are actually designed to withstand such an environment, are subject to serious export restrictions in the United States.
Slashdot Mirror
only maybe 25% or so does any useful work.
Modern turbofans have over 40% thermal efficiency. True, there are some additional inefficiencies associated with transforming shaft power into thrust - but since a turbofan and an electric ducted fan both use the same basic means of generating thrust, I see no reason to believe that an electric engine would do much better in that respect. (Also, when people quote wonderful-sounding efficiency numbers for electric motors like 95%, they are ignoring other large inefficiencies in the system, like battery internal resistance, voltage conversion and power filtering.)
Are you sure about that 1GWh figure?
Boeing 777-200LR fuel capacity = [180 kL]
Energy density of Kerosene = [37 MJ/L]
Energy content of a full tank = [180 kL] * [37 MJ/L] = [6.7 TJ] = [1.9 GWh]
Assuming the turbofan has [40% thermal efficiency], and the electric plane has [80% battery-to-shaft-power efficiency], this means the equivalent battery-powered plane will require about [1 GWh]. I am fairly confident this is accurate to the one significant digit at which I listed it.
As a sanity check, consider:
The turbines, of which the 777 caries two, have a naval equivalent which produce up to [40 MW shaft power] each.
The plane can fly for around [17600 km (max range)] / [892 km/h (cruise speed)] = [19 h] before refuelling.
Given [1.9 GWh] in the tank, flying for [19h] implies an average energy consumption rate of [100 MW].
[100 MW] * [40% (thermal efficiency)] = [40 MW shaft power], meaning that at cruise the engines are producing about [50% of max power] (which is not necessarily the same as being set at [50% of max throttle]).
Regardless, my basic point about the difficulties of charging stands even if I am off by quite a bit concerning the relative efficiency of kerosene turbofans versus battery-powered ducted fans.
The highest I see in that article is 5 MJ/kg. You said, "this could rise 10 fold in the near future". Where are you getting 50 MJ/kg from?
Human-carrying solar planes are unlikely to replace something like the Cessna 188, because there simply is not enough space in community airports for everyone to have their own 200 foot wingspan single-person solar slow-poke, even if that's what people wanted.
As to "small efficient electric light aircraft" - I already said that electric aircraft are plausible; they just won't be powered by solar panels while in flight.
I agree that (thin-film) solar is worth considering more seriously for a slow, buoyancy-lofted craft like a Zeppelin - but those would have to target a different market than something like a 747, because of their low speed and sun-blotting size. For now surveillance-like tasks, and maybe cargo transport to remote areas seem like the only good fits.
As you say, rising fuel prices could open up other possibilities later - I doubt large-scale, long-range passenger transport will ever be one of them, though. People are kind of the ultimate "time sensitive" cargo.
Are you volunteering to sit in a "modern airliner seat" for three days? Unless you are, it's a fair comparison.
You would need these batteries to charge very fast while on the ground, have long life-spans and cycle-count ratings for it to be economically worth it.
No, you don't need fast charging rates. With an airport, you have dedicated ground crews handling the preparation of the planes between flights, employed by the airline. So instead of refueling the plane, they just need to swap out some battery packs while the people are unloading. It should be entirely possible to build a fast-swap battery module into the underside of the fuselage, or thinner modules into the wings.
A battery-powered Boeing 777 equivalent would need (very roughly) 1 GWh in its battery pack. Someone recently claimed that Tesla is paying something like $200/KWh to build their battery packs now, which implies that a 1 GWh pack would cost around 200 million dollars. Even allowing for advances in technology (which are, of course, required in order to make such a battery light enough to fly in the first place), it would surely still be worth 10s of millions.
Such prices are not unreasonable considering the cost of the airplane itself - if only one or two packs are required per plane. However, even with battery swaps, you still need to be able to charge the pack in something like the same amount of time it takes to discharge it in flight: about 10 hours. Otherwise, you end up needing way too many spare batteries and charging stations.
For a 1 GWh pack, this means routinely charging it at about 100 MW. If that's not a "fast charging rate", I don't know what is. Sure, on a per cell basis 1/10th C isn't that much - but the sheer size of the thing is going to cause real difficulties for safety, cooling, etc.
Each large airport would require hundreds of chargers (every one equivalent in size and cost to a very large electrical substation) and a local generation capacity greater than most nation-states. The land-use alone would be prohibitively expensive, when you consider that large airports are usually found near city centres with astronomical property values.
Batteries, or solar cells, don't make thrust by themselves either. You'd still need the same turbofans, just with heavy electrical windings in the middle rather hollow combustion cavities. Electric motors tend to be quite a bit heavier than empty cavities are, so I'd expect the electric engine to be probably a bit heavier.
A turbofan engine has five main parts:
1) Ducted fan
2) Compressor
3) Combustor
4) Turbine
5) Nozzle
Of those parts, I believe that most of the weight, complexity, and expense is associated with #2 and #4.
In a hypothetical electric airplane #5 (the nozzle) is not needed, and #4 (the turbine) is replaced by the electric motor. It is not obvious to me which of those is heavier or more expensive, in the long run.
One might expect that #2 (the compressor) and #3 (the combustor) would go away also, but in reality they are still required, albeit in a very different form. Why? Because currently the only plausible way that an electric airplane could compete in range with a hydrocarbon turbofan design, is by powering itself with either metal-air batteries, or fuel cells. In either case, a great deal of air must continually be collected, compressed (not as much as in the turbofan, though), and "burned" (but at much lower temperatures than in the turbofan) inside the power source.
The compressor will get much lighter and cheaper, but still be required. I don't know if the reaction chambers and catalysts for the electric design end up being lighter or heavier than the combustor - but they will certainly be more expensive, if we go by current fuel cell prices...
Perhaps jets are wasteful and electric motor planes are less wasteful? I would guess so but don't know how to derate that.
Modern jet engines are very efficient (over 40%), assuming you spend most of the flight near their intended cruising speed. Electric might do better - but not more than 2x better, and probably less than that.
Thus in raw numbers that 10^10 could power 350 aircraft. Since batteries have loses assume 75% of that is more practical. Still that's more than the number of aircraft taking off per hour.
You forgot to divide the solar capacity by three to account for night time, intermittent clouds and fog, and the lesser amount of light available early in the morning and late in the afternoon.
Obviously I ignored that takeoffs use a lot of fuel. But that's factors of 2
The 750 average gallons per hour number you used is reasonable for a 737, even allowing for takeoffs (which are somewhat balanced out by the low-power glide into landing). However, many jet planes are a great deal larger than the 737; for example, a 777 or 747-8I burns about 5x as much fuel.
jet fuel is about 42MJ/kg. the current best flow battery is about 5MJ/kg. But recent advances suggest this could rise 10 fold in the near future.
Do you have a source for this?
I find it very difficult to believe that any battery design which stores its own oxidizer can ever compete with a hydrocarbon for "energy density", since the hydrocarbons get to cheat by not counting the majority of the mass required to complete the reaction (at least 3x as much oxygen is required, as fuel). My expectation is that the only kinds of chemical batteries which could even theoretically compete with hydrocarbon fuels, would be metal-air batteries since they get to cheat in the same way.
A solar-powered direct replacement for something like a Boeing 747 is impossible, period. Incremental technological development cannot get us from here to there.
Boeing 747-8I maximum fuel = [240 kL]
Energy density of Kerosene = [37 MJ / L]
Thermal efficiency of a modern turbofan engine = [40+%]
Flight duration = [16+ hours]
Energy required = ([240 kL] * [37 MJ / L] * [40%]) / [16 h] = [220 GJ/h] = [62 MW]
So, even a hypothetical 100% efficient solar-powered 747-8I replacement would require about 62MW of average (not peak!) power to operate. The maximum power that can be collected by a solar energy system (no matter how efficient) is limited by its surface area: it cannot gather more energy than what is present in the sunlight hitting it.
Maximum solar irradiance at Earth's Orbit: [less than 1.4 kW/m^2]
Upper surface area of a Boeing 747-8I: [less than 1000 m^2]
Maximum solar power available to a solar 747-sized object: [less than 1.4 kW/m^2] * [less than 1000 m^2] = [less than 1.4 MW]
Even an ultra-high-tech solar 747-8I replacement could not possibly generate more than about 2% of the power required to perform the same mission. It would inevitably need to fly much slower and lower (probably low enough for cloud shadowing to cause major problems), and/or carry a far smaller payload.
Barring a major (read: not foreseeable) physics or engineering breakthrough, true solar-powered jet replacements are not possible. Electric planes might happen eventually, but they will require refuelling or recharging on the ground, just like today's hydrocarbon-powered designs.
He's lucky he didn't go blind while making this. That fireworks clip, in particular, was just asking to get hit in the face with something burning and white-hot.
There *is* still such a thing as secure communications, you know.
For practical purposes - there really isn't for the average man on the street (in the West, at least).
Businesses (whether employers, vendors, or service providers) generally use some combination of phone, fax, email, and snail mail. All of those systems are thoroughly compromised. Email could theoretically be semi-secure - but that would require both ends of the conversation to be using computers that didn't rely upon millions of lines of poorly-vetted and/or proprietary code to function.
As for friends and family - many of mine are simply not tech-savvy enough to correctly use and maintain a "secure" computer communications set-up, even if I taught them how.
If you really think that the general public is capable of keeping their electronic communications private from the NSA using present-day civilian tech, you are either living in a fantasy world, or have a poor grasp of how computer security (and probably computers in general) actually work.
Did you even read what I wrote?
You don't have to use Skype, specifically - but the phone system, email (and snail mail, for that matter), Facebook, Google Hangouts, and pretty much any other modern communication system you could name all have the same problem.
And yes - refusing to call, text, or (e)mail people is a pretty good way to make yourself into a friendless (and likely jobless) recluse.
As far as I can tell based on the leaks from Snowden, and my own rather deep understanding of how modern computers work, the NSA is pretty much going to spy on me, my friends, and everyone on the internet regardless of whether I use Skype or not. Moreover, the main practical alternative to Skype in my life, is my cellphone which is no better as far as spying goes.
I am not "tolerating" the trampling of our rights; I simply do not see a meaningful technological alternative short of becoming a Luddite or a friendless recluse.
(I do not believe that Tor, encrypted email, etc. would actually be secure for my day-to-day communications, in practice. Too many other layers of the technology stack - the web browser, the operating system, the firmware, and my internet service - are readily compromised in ways that I cannot really do anything about. The "anonymity" provided by Tor would be easily pierced if I just used it to talk to all the same people that I know in real life.)
And why? Just so you can get laid? Lame.
Get your mind out of the gutter. People are not just sex objects, and I'm not interested in a long-distance relationship (the only kind that might require Skype), anyway.
How is it "unethical" or "immoral" for me to prioritize the other people in my life, over my own privacy?
The NSA are the peeping Toms, not me. You are blaming the victim.
I know it's hard to believe, but some of us Linux users do actually have friends, family, or business contacts who are members of the other 80+% of the population that uses Windows. My social life is a higher priority than tinfoil-hattery, even though I am not happy about the NSA spying on everything and everyone "just in case".
You left out #4: The errors in spelling or grammar are actually bad enough to obscure the meaning of the message.
Attempting to correct or clarify the message in such cases helps keep the present conversation from derailing due to misunderstandings; it's not just about training people to do better in the future.
Having said that, true examples of #4 are rare, unless the writer is either not a native English speaker, or is just being very lazy (as is common when texting). The writer himself is not in a good position to judge how confusing his own mistake really is, though, so people really ought to err on the side of just accepting the clarification, instead of calling anyone who finds poor spelling and grammar confusing a stuck-up jerk.
[5.8*10^7 s] + [1.16*10^-11 s]
That should obviously be a minus in the middle, not a plus; the escape is faster, not slower.
there is simply NO WAY that taking an extra 1/100th of a nanosecond to escape
Again, this should be "taking one 1/100th of a nanosecond less to escape", not "more".
I should really proof-read this stuff more carefully - but in this case it does not change the ultimate conclusion at all.
That Prius only reaches that very good efficiency as the engine can run at optimal load and optimal RPM all the time, running the generator, charging the batteries.
The 38.5% number is a measure of the peak thermodynamic efficiency of the engine alone; it says nothing about the usage patterns of the engine in the Prius.
A regular car or motorbike most of the time is either idling (0% efficiency) or running at sub-optimal loads and RPMs, both quickly lowering overall efficiency.
This is a good point. In theory, something like the Chevrolet Volt may be the best near-term solution, as it has a big enough battery to allow the engine to run almost exclusively at the optimal load, while still having good range like a regular ICE vehicle. Make it a plug-in hybrid if the grid in the area is decent (i.e., not India).
Many vehicles in India use two-stroke engines and are poorly maintained. A total efficiency as low as 10% for those vehicles may very well be a realistic number.
True. On the other hand, India has a really terrible electric grid too (30% losses, not 10%), and little money with which to fix the grid, buy modern four-stroke ICE vehicles, or buy cutting-edge electric vehicles (the only kind which can compete range-wise with an ICE currently). So anything they do is probably going to fall short of Western performance standards; trying to figure out which option falls least short is an interesting problem.
I never said our republic is healthy (we all know it's not)... just that demanding Congress make their decisions based on what might be the indirectly implied "will of the People" via the presidential election is not reasonable. Many of the ways in which America's political system is dysfunctional affect the office of President just as much as they affect Congress.
The ball gains momentum from the train in an elastic collision. The train loses momentum.
Or in other words: in the second question the ball is faster than in the first question and the train is slower.
Let [mA] be the mass of the smaller object.
Let [mB] be the mass of the larger object.
Let [vA0] and [vB0] be the pre-collision velocities of the two objects.
Let [vA1] and [vB1] be the post-collision velocities of the two objects.
Let [AB] = [mA] / [mB], which is the ratio of the lesser mass to the greater.
With a little algebra: [mB] = [mA] / [AB]
By the law of conservation of momentum: [mA]*[vA0] + [mB]*[vB0] = [mA]*[vA1] + [mB]*[vB1]
By substitution: [mA]*[vA0] + ([mA] / [AB])*[vB0] = [mA]*[vA1] + ([mA] / [AB])*[vB1]
By subtraction: [mA]*[vA0] - [mA]*[vA1] = ([mA] / [AB])*[vB1] - ([mA] / [AB])*[vB0]
By division: [vB1] - [vB0] = ([mA]*[vA0] - [mA]*[vA1]) / ([mA] / [AB])
Simplified: [vB1] - [vB0] = [AB]*([vA0] - [vA1])
Let [dvB] = [vB1] - [vB0] and [dvA] = [vA1] - [vA0]
By substitution: [dvB] = -[AB]*[dvA]
By division: [dvB] / [dvA] = -[AB]
From the above, we can see that the ratio of change in velocity for the train versus the ball, or the spacecraft versus the planet, is equal to the (negated) ratio of the smaller mass to the greater mass:
A large train weighs in excess of 10^6 kg. A tennis ball weighs less than 0.06 kg. Thus:
[AB] = [6*10^-2 kg] / [10^6 kg] = [6*10^-8]
[dvA] = [-130 km/h] - [+30 km/h] = [-160 km/h]
[dvB] = -[AB]*[dvA]
[dvB] = -[6*10^-8]*[-160 km/h] = [9.6*10^-6 km/h]
So technically, yes the train slows down - by an immeasurably small amount that is completely irrelevant for any purpose other than ensuring conservation of momentum. #1 takes a mere 0.45 seconds, but #2 also needs an extra 54 nanoseconds.
I would approve your answer here as pedantically correct... except that the application you have attempted to make of it to gravity assists is just dead wrong:
x-dV seconds
That's obviously invalid, and not helpful at all. x and dV are specified in different types of units (time versus speed), so one cannot be directly subtracted from the other like that. Repeating the math from above, but now for the gravity assist case:
A truly gigantic manned spacecraft (required for such a long journey) might weigh 10^7 kilograms, while an ice giant like the theorized "Planet Nine" might weigh 10^26 kg (like Neptune). The maximum plausible velocity change for the spacecraft from the gravity assist would be around 4 km/s.
[AB] = [10^7 kg] / [10^26 kg] = [10^-19]
[dvA] = [4 km/s]
[dvB] = -[AB]*[dvA]
[dvB] = -[10^-19]*[4 km/s] = [-4*10^-19 km/s]
Now that we know roughly how much "Planet Nine" could be slowed down by an encounter with our spaceship, we can calculate how much faster the ship will escape the planet's gravity well as a result. We'll use Neptune's Hill Sphere radius as a reasonable (and lazy) approximation for the size of the well.
[ship speed] = [2 km/s] Note: As in the train case, from the planet's frame of reference, the ship does not (in net) speed up; it only changes direction.
[planet dV] = [-4*10^-19 km/s]
[Hill radius] = [1.16*10^8 km]
[inbound time] = [Hill radius] / [ship speed]
[inbound time] = [1.16*10^8 km] / [2 km/s] = [5.8*10^7 s]
[outbound time] = [radius] / ([ship speed] + [planet dV])
[outbound time] = [1.16*10^8 km] / ([2 km/s] + [-4*10^-19 km/s]) = [5.8*10^7 s] + [1.16*10^-11 s]
The above formula is grossly oversimplified (since, unlike an actual elastic collision, this acceleration is far from instantaneous) - but should nevertheless
The point I'm trying to make, though, is 'if somebody doesn't vote, how do you determine their intention?' Answer me that. You say you didn't vote. So how is Congress, or the President, supposed to divine how you feel on, say, health care?
As I said to someone else in this thread, I think Congress should simply vote according to their own consciences, instead of trying to indirectly infer what a referendum on each issue would show. That's how a republic is supposed to work: you vote for someone you trust to make good decisions, and then let them do their job (or vote them out).
As to my own intention - the desires of my demographic are not unknown to Congress or the President; there just aren't enough people in the United States who truly share my views to form a politically relevant voting block (and we're not into bribery, either). The Government knows what we think; they just don't care, and never will unless the demographics change.
I would be a lot more likely to directly participate in the electoral process if America's voting system wasn't designed in such a way as to effectively disenfranchise anyone who can't at least come close to assembling a majority.
I do vote on referendum or ballot measure type stuff, because in such Yes/No contests my opinion actually appears on the ballot, unlike in the presidential Red vs. Blue vs. [Redacted] contest.
No it is not. Most of the stuff involved is 99% efficient, so I simply averaged it to 90%.
Sources? Here are mine:
1) In the USA, transmission and distribution losses are estimated at 6% by the EIA. However, India (the subject of the original post) has really bad infrastructure, in comparison. Their losses are estimated at about 30% by the World Energy Council. So, I was actually way too generous when I said "90% efficient" for this part.
2) The Tesla Roadster is said to have a battery pack charge/discharge efficiency of 86% in an article from Stanford University, which claims to be drawing from a source published by Tesla itself.
3) The National Electrical Manufacturers Association requires a minimum efficiency of about 92% for some large induction motors. However, I found an answer on the Electrical Engineering Stack Exchange site indicating that Tesla uses a slightly less efficient type of motor, and also that a ~97% efficient power controller is required, which brings the real efficiency down to ~88%.
Using the exact numbers I sourced, above: 88% of 86% of 70% of 42% = 22%, which is even worse for a coal-powered electric car than what I originally posted (because I was intentionally rounding up a bit to allow for future improvements).
That link about the Prius Engine is nice! However keep in mind: that would require all new cars to use engines like this. Which they hopefully do in not to distant future.
The extremely aggressive CAFE standards recently set by the Obama administration are already pushing things hard in that direction in the USA. Admittedly, India probably won't be buying many ICE cars produced for the US market in the next decade - but then, they won't be buying fancy electrics like a Tesla, either.
Interesting, but still, if you numbers are correct, this only applies to a Prius, which is a hybrid (half electric) which represents a very small percentage of all cars on the road,
The 38.5% efficiency is for its internal combustion engine alone; the fact that the Prius joins that engine to a hybrid-electric drivetrain does not effect that number.
and there are not that many cars with such efficiency either.
I picked the Prius simply because it's the easiest thing to find precise numbers for. However, a little poking around on the web suggests that a more typical current generation gasoline engine might be 30% efficient - which is still neck-and-neck with coal-powered electrics. Diesel engines are much better, at 40+% efficient.
You are also not considering the PRODUCTION and TRANSPORTATION of fuels, which also amount for a large % in reduction of energy.
angel'o'sphere left a lot of things out of his original ad-hoc analysis; I followed suit in the interest of making an apples-to-apples comparison. A more complete analysis would consider:
1) The efficiency of producing and transporting fuels - including the coal which ultimately powers the electric car in angel'o'sphere's original comparison, not just the gasoline or diesel for ICE cars.
2) Mechanical inefficiencies in the drivetrain of both electric and ICE cars - this will favour the electrics on average, since they usually don't need such an elaborate transmission.
3) The greatly reduced weight of ICE cars compared to comparable electrics (batteries are very heavy), which means that less energy is required to accelerate an ICE car in the first place.
...And a million other economic, environmental, and logistical factors, too, because energy efficiency isn't the be-all-end-all measure of technological, economic, or environmental superiority.
As awareness for health and the environment grows, and given that all ICEs produce fumes toxic for humans, I can predict there will be a law in the future PROHIBITING them all.
You do realize that the point of comparison in this discussion is COAL POWER, right?
I highly doubt that we will see a blanket ban on gasoline (or event diesel) internal combustion engines prior to a ban on burning coal. While it is possible (given enough money) to prevent "toxic" emissions from any hydrocarbon fuel, it is far harder to do so for coal than gasoline, ethanol, or natural gas.
All of the aneutronic fusion reactions you point out have a difficulty...
Interesting. I had heard about that issue for proton-boron, but was not aware that it applies to Helium-3 as well.
All that said, it'd be awesome if someone conquers the difficulties and makes either sort of direct conversion nuclear practical. I even support using tax funds to research toward those goals. But I see them as long shots...
I don't know that I would call direct conversion nuclear power (collectively) a "long shot", but certainly there is little reason to expect cheap net power from any of these schemes in the near term.
I did find the early Pollywell experimental results revealed by Jaeyoung Park's recently rather exciting, though. Of course, even if it gets fully funded and turns out to be fundamentally workable, that's still probably at least 15 years away from a commercial product.
and in the meantime, the market is going to vote with its dollars and go with what works today and is cheap!
Most of major the Generation IV fission designs have been proven workable, and I think some could be cheap enough - if the regulatory and political environment actually allowed them to be built in the West. But instead, we'll probably just keep extending the life of the existing decrepit Generation II installations, with their dubious safety and economic record...
Another huge advantage is the fuel and waste is not in the primary coolant. Having your primary heat exchanges being totally radioactive makes maintenance hugely expensive since its needs to be more or less 100% remote. the Machines are coming, but not quite yet.
This is especially true when you consider that high radiation environments are pretty hard on electronics, as well as people. Any electronics which are actually designed to withstand such an environment, are subject to serious export restrictions in the United States.