Top Gear - S12 EP7 - 14th December, 2008 - Discussion
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ROFL! Gotta feel for the Morris Morina owners club after this one :-D
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I thought James May did a brilliant review of the FCX clarity, he makes it seem almost like a good buy, but... I have not seen hydrogen fueling stations anywhere in NJ, second, and please bear with me you chemist and environmentalist freaks, if Hydrogen is the most abundant thing in the universe and you can even get it with a few solar panels and tap water... why in the living hell do I have to pay through the nose for it? if this thing was cheap enough I may consider it
on to the tesla test, I just knew this would happen, pretty good car, overpriced and battery power still needs to come along for it to be reasonable |
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It takes 20 to 100 square meters with cheap panels to produce a kilogram of H2 per day, depending on the latitude (within US; for most part, 20 to 40). Assuming you normally drive 12,000 miles a year, and the car is an efficient fuel cell hybrid, you'd need 200-250 kilos a year, somewhat less than 1 per day. Still, such a solar garden is going to cost as much as the car itself, or more if you account for the electrolysis hardware, the compressor and the tankage. Less space is required with more efficient solar panels, but they cost more. Quote:
The cost would be higher if it was electrolyzed rather than extracted in petrochemical processes as today. |
the biggest problem when looking at hydrogen as your fuel of the future is that it's terribly energy inefficient.
i will summarize some points that i found while reading my chemistry book: at first glance hydrogen can produce a massive amount of energy per mass unit 120 MJ/kg that's really impressive and about 3 or 4 times better than petrol. but when we are talking about fuel in a car we have to look at how much energy it can produce per unit of volume and here hydrogen puts out a measily 2.8 GJ/m³ (that's 1000 litres) at 35 MPa in its gaseous state. (i don't have the exact number for petrol here as it's not written in the text, but when i look at the graph i have it's about 1/10th of petrol) when hydrogen is a liquid things look a bit better, where we have about 8.5 GJ/m³ but that means cooling the hydrogen to 20 K (that's -423 °F and -253 °C) which takes in itself a huge amount of energy. all numbers are taken from Housecroft and Sharpe, Inorganic Chemistry 2nd Edition (german version) now the biggest problem probably is obtaining the hydrogen... the easiest way to obtain it is splitting water into Oxygen and Hydrogen. sounds good eh? but then you have to realize that this process needs energy too and in the end we are just recombining the 2 elements to form water again. so the energy we invested in the first place will be produced again when burning the hydrogen so we end up neither gaining nor loosing energy. which is not very efficient right? so in the end i think i will have to quote what nthfinity said once on this board (sorry i don't know the exact wording but it went something like this) "the future of transportation is not the car it will be something completely and radically new." |
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as James said "it always sticks to something" this is just a not complicated way of saying that hydrogen is an extremely reactive element and thus can only be found entrapped in a chemical bond with a different atom or whatever you like. for example petrol or gas is just carbon with a huge amount of hydrogen in it. C6H14 - Hexane has roughly speaking 2 hydrogen atoms per Carbon atom. so now you can say that in oil (this is just an example) hydrogen is the most abundant element in petrol (petrol is made up of over 100 different alkanes (that's what you call these carbon chains with hydrogens attached to them)) so basically being ignorant and asking for a low price jsut because something is abundant is not going to get you anywhere, because you will have to pry the hydrogen out of it's already existing chemical bond. hey if you have read until here then congrats to you :) |
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1/10 is about right. So if you had the car using compressed H2, the tanks would take 12% to 20% depending on the pressure (there are 70-MPa storage tanks on the market). But then a 20-gal tank is for a 600-mile range, which you don't really need. These 20-gal tanks are there only because it costs very little to enlarge the tank. With half that capacity, the tank will take just 6%-10% of the car. It's not a big compromise. Of course, tankage weight needs to be worked on, so that this tank doesn't weigh 200kg. Quote:
OTOH, the military is already interested in liquid hydrogen. Fuel cells are not necessary. And cost is less of an issue there. Quote:
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http://www.blogcdn.com/www.autoblogg...kson_tesla.jpg
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LOL ....someone is desperate for customers.
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Yet another reason never to cite Top Gear as a factual source.
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It's not the first and not the second time Top Gear plays that scene. The comment about 16 hours is somewhat ambiguous. It's 16 hours if you have the most basic household wiring, not designed for an electric stove, multiroom AC, or other high-power amenities. However, if you install some higher-amperage wiring, which costs between $100 and $300, then you can indeed recharge an electric car quickly, probably in the 3.5 hours he quotes. |
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