Hydrogen is really just an energy carrier. Where will the energy for electrolysis come from? And electrolysis is actually quite inefficient. In fact, 3/4 of your arguments for hydrogen actually applies to electric. Fuel cell is also far from ready as a technology. On the other hand, electric or plug-in hybrid has the most potential. There are many ways of generating electricity, including solar, wind and nuclear. Even if the electricity came from coal generation, it is still cleaner according to a study done by CMU (http://www.greencarcongress.com/2007/06/cmu_plugin_hybr.html , http://wpweb2.tepper.cmu.edu/ceic/papers/ceic-07-04.asp). By centralizing the energy generation, you can replace a dirty source much easier than the dirty cars roaming around the street. It's also easier to manage pollution problem.

Electricity distribution is also not as big of an issue as it appears. Electricity has already been an inseparable part of our lives and the infrastructure is well established. One can argue that charging a electric car is even more convenient because you can plug the car in places where an outlet exists (as oppose to going to a refilling station.) Range may be a problem, but that is why plug-in hybrid is such a good technology to bridge the gap until better battery technologies become available. Alternatively, one can treat battery as replaceable component and have replacement stations just like gas stations. I believe there are people working at that model in Europe already.

Biofuel is definitely more of a problem than a solution from the way it is implemented... but i will keep this reply short and stop for now.

> 核能地熱能則地球原本是太陽分裂出來

純粹天體物理學上的更正:

1. 現今一般認為, 太陽和行星, 是各自由星塵凝聚而成, 行星並非由太陽而來. 沒錯十八世紀是有假說曰: 遠古時有高質量星體由太陽引出物質, 再形成行星. 但力學計算的結果, 這種系統不會穩定, 引出來的物質最終亦會回歸太陽.

2. 現今一般認為, 地熱的來源, 大部份是地球內元素的核蛻變所產生的能量.

3. 除了氫外, 其他元素的來源, 一般認為是 (1) 恆星內的各種核反應的產品 (2) 較高原子序的元素, 是一些高質量的太陽在生命終期形成超新星, 最後超新星爆炸, 產生高原子序的各種元素, 並拋到宇宙各處, 然後再形成其他的天體. 所以你眼前的所有東西, 可以說大部份都是由恆星而來的. 你說 "核能...原本是太陽(分裂)出來" 字面上說得通, 但跟現在我們說的太陽能可說沒有關係, 因為現在談的太陽能, 是由 (1)我們的太陽系的太陽的 (2) 核聚變產生的輻射能.

其實, 我們在談石油替代品時, 往往會忘記石油除了是能源, 也是重要的化工原料. 現在有成本上可行的石油化工替代品嗎?

我用的數字﹐全部從經濟學人那份報告出來﹐你可以自己去查證。

Quote from "Grow your Own" - Economist

A study by America’s Departments of Energy and Agriculture suggests that even with only small changes to existing practice, 1.3 billion tonnes of plant matter could be collected from American soil without affecting food production. If this were converted into ethanol using the best technology available today, it would add up to the equivalent of 350 billion litres of petrol, or 65% of the country’s current petrol consumption.

Just enough time for a short comment: "只需要美國糧食總產量的1%﹐就已經足夠製造給美國所有汽車用的生物汽油。" is simply illogical. How is it possible that we need to put 99% of what we grow to feed us, but just 1% is enough for all the cars in USA?!!! Are our stomach many times larger than our cars' gas tank?!!!
'Economist'? Forget it! It became so biased nowadays.
There are hundreds of them available. Why select and quote this one?

Just to add on to the points by 麥當勞...

I am not sure if 1% is the exact number... but it is entirely plausible. To be clear, hevangel said 1% of total _food production_ and not food consumed. Honestly, I think we waste more than 1% of the food/biomass we grow (I mean, how much of an orange is skin :-P)... but to take advantage of those biomass, I believe we need 2nd generation/cellulosic ethanol, which is not quite there yet.

To be fair, biofuel does have major problem. For example, if people are clearing forest (worse if rain forest) to grow those cash crops for biofuel:
http://www.sciam.com/article.cfm?id=biofuels-bad-for-people-and-climate

As for Economist being a bad source... please bring forth the better ones. I personally think it's credible but if there are even better source with more accurate information, I'd love to know about it. We are all learning here.

The Bio-mass for biofuel doesn't have to be food crops and actually it's better if it is not food crops. Just like Ken said, we need 2nd gen biofuel technology. But if you just crunch the number on the theoretical limit, biofuel is very promising.

Solving the Biofuels vs. Food Problem - Times
In the biggest such study to date, scientists led by Kenneth Vogel from the U.S. Department of Agriculture and the University of Nebraska-Lincoln performed long-term, large-scale field studies on raising switchgrass as an energy crop. Farmers in 10 fields of 15 to 20 acres each in Nebraska and North and South Dakota grew switchgrass over five years, and kept track of how much fuel and fertilizer they used during the trials. Vogel and his colleagues showed that switchgrass yielded 540% more energy as a biofuel than the amount of energy used to grow, harvest and process it. (Corn ethanol yields just 25% more energy.) Greenhouse gas emissions from switchgrass fuel would be 94% lower than emissions from petroleum fuel — almost carbon neutral. Previous studies had come up with similar numbers in small-scale trials, but this was the first study on the level of a working farm. "The idea is that we won't be replacing food with fuel on prime land," says Vogel. "This study shows you can use switchgrass as an energy crop on marginal land and get the same environmental benefit."

I think Fung Huen is right on wording. I also overlook what H said. Plant matter is not necessary food. The articles refers to Biomass which include farm industry waste, dead plants/animals and shit.

Actually I don't care those biomass because human does not eat those biomass. Those biomass can be converted into energy no doubt. The "1.3 bil" number is old data in 2005 and it should be increased much by now. The problem is still efficiency, becuase you can't extract every energy from the biomass.

"1.3 billion tons of biomass would yield 75 billion gallons-equivalent"...I did not do the math, just quote something here. http://ergosphere.blogspot.com/2005/12/what-can-you-do-with-13-billion-t.... That is huge: It is close to US car consumption if 100% utilized.

我的確認同 H 有需要拿出他的 source 的數出來計算一次, 但係所謂"大家应能發覺这根本唔使計都知係錯"到底係乜野態度? 你當讀者係職業打手呀? 你唔計就直指Economist 係"由財团操控、以牟求各种利益為尚的雜誌", 咁唔係 ideological 係乜野?

你篇文個 source 在這裡:
http://www.economist.com/specialreports/PrinterFriendly.cfm?story_id=115...

另外你指 "60% of oil is used by automotive fleet in the USA" 這個說法好驚人, 我好有興趣知道來源, 與及為何汽車的用油量比起飛機與及工業還要多足足一倍。

另外也講講"物質守恆定律", 其實無論點燒物質都係守恒, 守恒與否根本無關。個主要分別係同樣的重量, 係 biomass 還是 oil 的 chemical reaction energy 較多. 我無數字係手, 但要估都係 biomass 應該係 oil 多, 否則生物進行過程就會選擇食更高效能的石油, 但當然不可能超過 1:10 或 1:100 那麼極端.

plant matter or biomass for sure is not the same as grain... so I am not sure if I understand the argument.

and really... please give reference... for example... where is the 350 million ton of grain come from? I found this:
http://www.fas.usda.gov/grain/highlights/2002/02-02/us-canada/USDATA.pdf
I guess it's close enough?

And then there's the petrol consumption
http://www.eia.doe.gov/basics/quickoil.html

And 邪離子... what's FBR?

First thing first. From the data provided by R , the percentage of oil consumption by cars in the USA should be 9253000/20687000 (= 45%). Since the very figure wasn’t found by then, I have to calculate it from other related figures from more than one source. While I don’t think you guys will be interested in the details, 但確係唔講唔知,原來加侖都有兩种制式: In UK, 1 gallon = 4.546 litre. But in US, 1 gallon = 3.768 liter.(即相差近兩成) So I think I should share this info, if not lesson, with you all.
Therefore, the correct weight of gasoline used by cars in the USA should be:
0.515 billion tones X 0.45/0.6 = 0.386 billion tonnes.
And 0.386 billion tonnes is 55 times of 0.007 billion tonnes.
The 350M figure came from p.26 of ‘Plan B 2.0’ (still require simple calculation), 而它的reference也是出自usda.
I used to think that it goes without saying that extraction of biofuel from biomass is basically a distillation process. So the weight of biofuel produced must be substantially less than, thus lighter than, the weight of its source (ie. Biomass). 正如你不可能從一斤花生提煉出多於一斤(更遑論55斤)花生油般。And it is further ascertained by the same quote above from Economist. 而我一直以為這真是不言自明的,所以當我提「物質守恆定律」時,我已恐會比人話我畫公仔好畫出腸添,點知竟相反…
至於石油与生化油的能量输出效益比较,近年众新闻報导都指出gasoline is better.

45%, or even just 20%, is enough to prove beyond any reasonable doubt that the ‘1% of food production’ statement is grossly untrue, which is the original purpose.
But please don’t forget the forest, don’t lose the big picture. Why we get to verify the truth of this statement of fact in the first place is that we are encountering a big problem called Energy Crisis. If we can’t get the fact right, or even worse, if we mistreat some falsehood as truth, then how can we possibly solve the very problem? Maybe even worse, those being misled, instead of becoming part of the solution, will become part of the problem. And it isn’t an exaggeration. If someone mistakes the above statement as true, then he will naturally oppose to other more radical yet necessary measure(s) of solving the worsening problem.
It can be strongly felt that Mac got upset lately, though it’s never my intention. All I can say is that I realize many people around the world are already suffering from the fuel and food (which are closely related) crises, let alone dying! So I felt and still feel I shall get the things straight somewhat assertively. Unlike the media moguls, I don’t have a billion dollars nor a thousand staff behind me, so I get to make my lone voice loudly. Call it a strategy if you like; Call it a strategy for the weaker side if you like.
BTW, am I ideological? Of course I am. Yet all thinking people are. Hitler was ideological, but so was Gandhi. But that doesn’t mean they are the same. What I am against is 有人以ideology為藉口而行「因人廢言」之实。I find this kind of trick distasteful. That is a version of smear tactic we often see in political elections.
我信廣大的Inmedia读者也希望这里的言论是對事非對人。