Re the hydrogen solution to personal motorized vehicles vs. a clean world.
Hydogen comes directly from fossil fuel, electrolysis or another fueled process. So, with efficiency losses, it would take more energy to release hydrogen than it develops.
Also, if we power our vehicles plus our current (no pun intended) load of electrical “necessities,” where will the extra power come from? Oil? Coal? Nuclear fission/fusion? Wishful thinking?
Power plants are more efficient at utilizing energy from fossil fuels than cars and pollute less.
However, the the mechanism for energy generation in the Hydrogen Economy are new, state-of-the-art nuclear power plants. Although nuclear power plants are regarded poorly in the public’s mind, they already produce 20% of this country’s electricity, and new plants (most existing power plants are at least 30 years old) do not pose the same risks as the old ones. Radioactive byproducts can be fairly safely contained, and the relatively low volumes that are produced pose a far lower long-term threat than the millions of tons of CO2 and other pollutants that are constantly being released into the environment by traditional sources of energy. France produces 76% of its electricity from nuclear energy.
Of course, breakthroughs in renewable energy might also provide efficient, economic sources.
This is my first post to this list, and for various reasons, the connection to the “trees” thread was muddled. The point was, most attempts in this direction do not result in a net reduction in CO2 or fossil fuel consumption–they may, and often do, as the “tree” piece points out, localize the negative effects in a NIMBY manner.
dtilque, if there is a column on fuel cells I couldn’t find it. I guess I’ll have to post a query to the wizard…
Ronald Reagan once remarked that plants and trees are the biggest sources of pollution. Can someone explain the logic underlying that conclusion?
Jeremy Rifkin has some very cogent arguments regarding the hydrogen as the fuel of the future. I saw him a while back on C-Span but have not read his new book. From wood to coal to petroleum we have gone, each time utilizing more concentrated forms of hydrogen. Next, hydrogen and hydrogen alone from the start. We don’t have the technology to do this quite yet, but when we do, we’ll have a fuel with the sole biproduct of pure water. Breathe Exhaust sez: Don’t hold your breath!
Another question: What is the half-life of nuclear waste generated by nuke plants? Isn’t something like 24,000 years? Humanity must safely store this hot stuff for longer than civilization has so far existed. You heard about Yucca Mountain in Nevada? They want to bury the hot stuff and leave warning signs in about 100 languages, including hieroglyphics and pictograms. The message: Don’t disturb this stuff! It will cause you much harm! Yeah, that’ll work. Mankind has a great record obeying warnings. Like Eve with the apple. Another proposal was to start an order of monks to pass down the legend of the stuff under the mountain to keep future people from monkeying around with it.
I don’t knowabout France, but the promise for electricity too cheap to meter never panned out here in the U.S. Our nuclear program was government subsidized to the point of embarrassment. Not to mention the cost of decommissioning all those old plants built in the 50s and 60s.
As for trees, most people in the world are too poor to think about planting them. They still need to cut 'em down for housing, fuel, and a few years of grazing land. Hell, their are a billion human beings who scramble daily for anything they can grab to build a fire for cooking and heat. In far flung regions of Africa, Asia, and South America, SUV gas mileage is not much of an issue.
Breath Exhaust name most apt for this thread. I chose the handle at random, from old Ultravox song, “All Stood Still,” has a line, “We breathe exhaust at the holocaust…” I don’t bother with thinking up cool handles anymore, I just assume they’re all taken.
Long answer: high-level rad waste is, of course, a mixture of isotopes. Each isotope has its own half-life, of course, but the mixture does not (the decay curve doesn’t look anything like the decay curve for a single isotope).
The exact mixture of isotopes resulting from nuclear fission can’t be predicted, any more than we can predict when a particular atom of uranium will undergo decay. Nonetheless, we can speak to the average mixture produced, just as we can assign a half-life to, say, [sup]238[/sup]U. We can then combine all the decay curves, and get the decay curve for the lot.
The Effects of Nuclear Weapons (p. 343, IIRC, but I won’t swear to that) gives the total decay for nuclear waste as:
l[sub]t[/sub] = l[sub]0[/sub][sup]-k*t[/sup]
with t measured in hours. At about six months out, there’s a “knee” in the curve where the constant in the exponent changes from -1.2t* to -2.3t*.
Net-net: Rad waste decays to the radioactivity of the original ore in about 600 years. if this is your criterion for “safe”, then this is the amount of time it must remain isolated.
The Oklo fossil reactors indicate that, with no precautions taken, high-level rad waste (and its decay products) remains isolated from the environment for hundreds of million of years. The “nuclear waste disposal problem” is a crock of…ahem, manure.
He was probably a bit mixed up, but was on the right track nevertheless. What most people don’t realise is that agricultural crops are major pollutants. Approximately 20-30% of all of our greenhouse gases are produced from farms, and only a small percent of that is methane from livestock. Plants uptake nitrogen as part of their normal life cycle, and this nitrogen is released into the air. Add to this the nitrous oxide that is released from the soil from artificial fertilisers and you have an awful lot of the stuff being released. As for carbon dioxide, a major greenhouse gas, all carbon dioxide is fixated in the plant, often converted into glucose, but it stays there just the same. If a plant is felled but not harvested, then any carbon it had absorbed is released through decomposition or through fires (many undeveloped nations will burn agricultural areas to increase the nitrogen in the soil, without realising the consequence of the carbon dioxide that is released in the burning process). That carbon and nitrous oxide enter our atmosphere and contribute towards the greenhouse effect and acid rain, respectively.
Trees don’t fixate nitrogen themselves, but many cover crops such as clover are used in farms to fixate nitrogen in the soil for use by the cash crop, such as corn or tobacco.
Welcome to the SDMB, nick.baker, and thank you for posting your comment.
Please include a link to Cecil’s column if it’s on the straight dope web site.
To include a link, it can be as simple as including the web page location in your post (make sure there is a space before and after the text of the URL).
Cecil’s column can be found on-line at the link provided by Duck Duck Goose.
“Not in my backyard” thinking does not apply to CO2 which is not a pollutant in the classical sense of being bad for us to breath but is bad on the global scale because of its greenhouse effects. The point of a hydrogen economy is that hydrogen is a very ideal energy storage medium. I agree with you that some discussions of it fail to point out that the hydrogen must still be obtained somehow and how “green” the method for obtaining it is determines how good a solution it is. Still, you have a lot more flexibility once you remove the problem of energy generation from hundreds of millions of point-sources (vehicles) to plants that would produce the hydrogen, so it would greatly facilitate using cleaner ways to generate the power.
I’d like to point out something. Nuclear energy is not cheaper than traditional coal or natural gas. I don’t have any proof of this naturally, besides my memory of Sustainability class. If someone has some proof otherwise I would be more than willing to concede, but for the time being, I submit that Nuclear has failed or is in the process of failing in the US, not because of the percieved danger, but because of the cost. Especially now that security must be hightened.
About France’s dependance on Nuclear Energy… It is true, but France is a socialist economy. Governments can do expensive unprofitable things where capitalistic corporations might be wary.
Hopefully there will be huge advancements in cold fusion alongside superconducting materials in the next 50 to 100 years. Either would greatly help the energy economy. Over 50% of the energy that is generated at the power plant is lost in transmission. Another remembered statistic. (I wonder if they include that loss in calculating the efficiency of coal/natural gas.) Superconducive power lines would increase the efficiency. If cold fusion is perfected, then we could mine… uh I forgot what it is, but there is supposed to be plenty in the oceans… starts with a “d”. I want to say deuterium. Anyway, we could then generate as much h2 as we need. Efficiency loss due to transmission of hydrogen is much lower than electricity.
Yes, the word you’re looking for is deuterium, which is a naturally-occurring, non-radiactive isotope of hydrogen which is found in sufficient quantities in the ocean. If we could get practical fusion going, we would, if not solve the energy problem, at least put it off for tens of thousands of years. But it wouldn’t be cold fusion: That never had any promise at all, and was based entirely on the misleading claims of two fellows who ought to have known better.
Unfortunately, the future doesn’t look too rosy for hot fusion, either. It’s always been predicted to be at least 20 years in the future, but we never seem to get any closer to it. Nor are we likely to get any closer, at this point: There are currently no fusion experiments going in the U. S. Apparently, the funding for such research just doesn’t exist. The few physicists who are still working on fusion have to disguise their research in other terms, to be able to even get computer time.
Note that “hot” fusion doesn’t solve all the problems, either (although it ameliorates quite a few of them).
The easiest kind of fusion is deuterium-tritium (D-T). Tritium, of course, is a weak beta emitter with a half-life of (IIRC) 12.3 years. It doesn’t occur naturally in any significant amount, and has to be “bred” from [sup]6[/sup]Li. Fortunately, D-T fusion is neutronic, and the neutrons given off can be used to breed tritium from lithium. “Sweeping” the tritium out of the lithium is a non-trivial engineering problem, however.
Straight deuterium fusion (D-D) requires about three times the “ignition” temperature of D-T, and is also neutronic (it seems naïvely as if the reaction ought to be D + D = [sup]4[/sup]He, but the energy liberated by fusing the two deuterons is more than enough to liberate a nucleon, which has a 50% chance of being a neutron). D+[sup]3[/sup]He is aneutronic, but there are side reactions which are not, and which will occur in any fusion reactor. It also has an “ignition” temperature about ten times that of D-T. Higher-order fusions (e.g., [sup]11[/sup]B+p, often mentioned) may not be achievable in a controlled environment. p+p (solar-type fusion) is a weak-force-mediated reaction, and occurs at the rate of about 10[sup]-20[/sup] (again, IIRC) of D-T at any given temperature.