h a l f b a k e r ynon-lame halfbakery tagline
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
A country like Thailand has good natural resources, like Sun and rain, but relies heavily on imported oil and coal for energy. It's a shame that the natural resources are not used more effectively.
Just for fun, I tried to calculate how much woodland would be required to source the countries electrical
power requirements.
Assuming some poor efficiencies of say 5% for the total system, but average incident energy of 800W per square metre for 11 hours per day, and an electrical network consumption of about 40GW, the land required would be in the order of 2185 million square metres. This is an area of land which is about 48 kms by 48 kms.
Probably it would need to be bigger for fire breaks, and allowance for transportation and cycling of cutting and growing, but I think it shows that the principle is possible.
Geosequestration
http://en.wikipedia...gical_sequestration
[BunsenHoneydew, Dec 19 2006]
Carbon capture and storage
http://en.wikipedia...capture_and_storage
in more detail [BunsenHoneydew, Dec 19 2006]
Deforestation
http://en.wikipedia...orest#Deforestation
18,900kms2 per year! [Ling, Dec 19 2006]
A very good paper which describes why this isn't such a good idea.
http://petroleum.be...PS-BiomassPaper.pdf
Oh, well. [Ling, Dec 19 2006]
Algae for fuel and CO2 capture
http://www.google.c...6%3BFORID%3A1&hl=en
at the energy blog [BunsenHoneydew, Dec 19 2006]
An algae to biofuel implementation
http://thefraserdom...olix_biofuelsc.html
100 times the yield per acre of other crops [BunsenHoneydew, Dec 30 2006]
Distribution and availability of Solar Energy
http://cms.ises.org...ls/307/solarrad.PDF
average power for various regions and the effect of angled rays [afinehowdoyoudo, Dec 08 2008, last modified Dec 14 2008]
Solar panel efficiency "as-installed"
http://www.treehugg.../powering_20000.php
20 MW from 100 hectares peak output [afinehowdoyoudo, Dec 14 2008]
Please log in.
If you're not logged in,
you can see what this page
looks like, but you will
not be able to add anything.
Annotation:
|
| |
Hmmm. I'm unsure about the notion of setting fire to a whole bunch of trees. It just doesn't sound environmentally friendly somehow. |
|
| |
I do appreciate that if you're going to make energy by setting fire to things, that perhaps it would be better to harvest trees, rather than coal. But I can't help feeling uncomfortable about it. |
|
| |
For some reason, if you boiled the trees down and made alcohol from them, and burnt that, I'd be happier - but that's a purely emotional response - not sure it's rooted in anything that makes any sense. You could at least use the left-over bark, fibres and other bits for paper-making, clothing, basket weaving, or something. And, if you still needed to, you could set fire to them afterwards. |
|
| |
... a little rusty here but I think you need to check your numbers. |
|
| |
800W I think is a little optimistic. it might be that in noonday sun (maybe), not sure. |
|
| |
More importantly, I think total efficiency of the timber growing cucle would be well under 5%, by several orders of magnitude. |
|
| |
but I like your way of thinking. A country could easily devote 100 times that area for energy production. |
|
| |
I've seen figures of 1000W/m2 for insolation, so 800W doesn't seem out of the ballpark. |
|
| |
There was a French pilot project that did just this, with coppicing willows. They also exhausted all the waste gas at ground level into the forest, so the willows could consume it, capture it, and to encourage their growth. |
|
| |
[phlish] I suppose trees might be preferrable because they are renewable, and, if the grow/cut/burn cycle is rotated (as it would have to be if this were to be a sustainable powersource), you'd be planting/growing as many new trees as you cut down and burnt. |
|
| |
Carbon sequestering is also something that trees do for you automatically - coal is a longer-term form of sequestered carbon, that generally (i guess) takes longer to sequest than it does to release. |
|
| |
You probably get more wattage pound for pound by burning coal, and it is probably cheaper to extract - but it is limited, and, like oil, gets more expensive the rarer it gets. Trees are just a matter of having enough spare land, and the people to 'farm' it. |
|
| |
Yes, some trees will give you a better price as lumber - but not the sort of fast-growing coppicable trees that (I presume) we're talking about here. |
|
| |
If the trees are planted just for this project, the amount of trees in the world goes up, so it's all good. A powerplant optimized for burning wood should be easy to make, so efficiency versus coal isn't really an issue. |
|
| |
Are trees the best plants for converting sunlight to fuel energy? An annual, such as American corn, or maybe sugar cane, may do better. Although the work of harvesting must be taken into account. (Hmm, a plantation that grows a food crop with burnable stalks, and just burns the food for fuel when the food market is bad.) |
|
| |
Is it more efficient to send electricity over wires than to transport the wood to the cities for people to burn? I certainly think so. |
|
| |
[baconbrain] Algae are good for efficiently-produced biomass. Some of them can be used to produce oils for biofuel. |
|
| |
Addis Ababa, Ethiopia is an essentially wood-powered city (or it was twenty-odd years ago). This was only made possible by the import of fast-growing eucalyptus trees from Australia at the end of the nineteenth century - before that, the capital had to keep moving around, because it kept exhausting local timber supplies. Unfortunately, these fast-growing eucalyptus trees have been bad for the soil (I forget how, exactly, but erosion might have something to do with it). |
|
| |
Eucalyptus: also grown in Thailand for cheap scaffolding and, I think, paper.
When they are cut, the roots sprout again: hence zen_tom's comments about coppicing, and the sub-title. |
|
| |
Mmm: not a new idea. Well, I agree that burning wood for power is ever so slightly baked. I thought that setting aside 48kms square to supply the whole country's electrical power was more of an idea for a system. |
|
| |
By the way, another similar idea is on its way. |
|
| |
I recall seeing cylinders of cellulose: compressed plant matter used a subsitute feedstock for coal plants. Some cellulosic biomass plants (eg reed canary grass) that has gotten attention lately could be directly burned as you suggest. |
|
| |
/ Burning forests not only releases carbon into the atmosphere, it also eliminates more of nature's scrubbing mechanism./ |
|
| |
Corn scrubs too, and when I eat it, I release the carbon into the atmosphere. We should leave the cornfields alone, and use coal to produce tasty margarine using the Fischer-Tropsch process. |
|
| |
When England started using coal, it was seen as an inferior substitute for wood; since there wasn't enough woodland to supply the country's heating needs, however, coal was a necessary if dirty substitute. |
|
| |
In areas with small populations and lots of woods, using wood for energy might make sense. Even there, though, it would make more sense to use wood for paper and then use scrap paper as fuel. |
|
| |
Carbon sequestration is a totally unproven technology with massive risks involved. Besides, we need the -02 |
|
| |
I don't follow your point, which I think is: Growing wood, to later burn it, is risky. Are you comparing to burning oil and coal, or something else? |
|
| |
The wood-powered society makes even more sense if there is a centralized way to turn it into charcoal with minimal emissions, and thus avoid the polluting wood smoke. I can imagine a government minimum-emission charcoal factory then then parcels out the charcoal for individual small users. |
|
| |
//I don't follow your point// |
|
| |
Oops, I should have been specific in that I was referring to geosequestration. It's an expensive, unproven and potentially lethal (if any leaks to ground level) idea for trapping CO2 underground. And it's dumb, because it sequesters all those oxygen atoms, which we need up here on the surface. |
|
| |
...and I thought that CO2 was something that we had too much of...
I thought that one output of trees, while growing, was oxygen, so they must be separating carbon from oxygen in some way. I can't see any problem with this. Besides, how many countires could grow 48km x 48km of woodland, before replacing what is disappearing in South America per year? |
|
| |
presumably, growing the trees on the same patch of land over and over again would ensure that the power plant running on these trees does not actually give off any net amount of CO2, as the trees must convert the same mass of CO2 back into fuel before they can be used. I would also imagine that the equippment needed to clearcut a coppice would be less damaging to the environment than the equippment needed to mine coal (and possibly safer for the workers!) |
|
| |
While your power plant should have an efficiency similar to a coal burner (about 35%) your equations are based on the energy of the full spectrum of the sun beating down on the land, which is inaccurate. The trees are not likely to cover 100% of that land at any given time, indeed, as I can still see to walk beneath old growth forests, I would be surprised to see them covering more than 50% of the land with light capturing branches. Beyond that, they only use a narrow band of the spectrum, less than 1% of the total output of the sun I would imagine, and they operate at less than 1% efficiency at capturing that section of the spectrum. Once captured, you may then burn that for fuel at about 35% efficiency. |
|
| |
If you're really trying to harvest the energy of the sun, why not do it directly. Modern solar panels have a 20% efficiency. |
|
| |
After your comment, I thought I would check what the energy conversion efficiencies really are: See link. Average product over the whole year, for Eucalyptus is 0.345W/m2. If average insolation is around 300W (24hrs a day, all year), that's an overall yield of 0.1%, before energy costs for harvesting, transporting etc. |
|
| |
Ah, that does not look like .1% to me. You have a small mistake in your formula. The output of a biomass farm is in Watt-hours, not Watts (or Joules in the paper you reference 3600 Joules=1 Watt-Hour) |
|
| |
By the paper you reference the production of eucalyptus is about 1.2 Watt-hours/year/m2 |
|
| |
Insolation is measured in Watts. To get Watt hours you multiply Watts by the amount of hours that the area is in sunlight. Using your 300W/m2 figure as a base, lets assume 12hours of sunlight a day. Oh, and lets assume half the days are heavily overcast. That would give us 657,000 Watt-hours of power. |
|
| |
Which makes the efficiency about .00018% |
|
| |
No, I used (6.3) gross heating value is 109GJ/ha-yr.
That's 0.345W/m2 average power.
That is the actual output, with the conditions of the area under test.
If you want to start reducing the amount of insolation from 300W/m2, then the efficiency is improved from terrible, to not quite so terrible. |
|
| |
By the way, you've written m3 twice. I know you meant m2. |
|
| |
[Ling] //...I thought that one output of trees, while growing, was oxygen, so they must be separating carbon from oxygen in some way.// |
|
| |
Yes. It's called photosynthesis. |
|
| |
I wasn't referring to the trees, I was referring to geosequestration [link], aka carbon capture and storage [link], which is about liquefying whole CO2 and pumping it into the ground or deep ocean. |
|
| |
Trees liberate oxygen. Trees good. Geosequestration bad, mkay? |
|
| |
BTW it's 8 to 20 times as efficient per acre to use algae ponds. [link] |
|
| |
Thanks for the correction on square vs cube. But you are still comparing Joules to Watts. That is like comparing distance to speed. |
|
| |
Ok, 109GJ/ha/year is 10.9MJ/m2/year (10,0000 m2 to th ha) |
|
| |
10.9MJ is 3078Wh (3600J=1Wh) |
|
| |
So a Square Meter of Eucalyptus coppice produces about 3kwh per year |
|
| |
If that same square meter were in a 300W flux of light 24 hours a day, 365 days a year it would receive 2628kwh in that year. Or an an average of that. |
|
| |
Ok, with that I get .11 percent efficency. |
|
| |
Which is still pretty much in the terrible category. |
|
| |
Depends. That's efficiency per acre, not efficiency per dollar spent. Regions with cheap land and not much money might find this attractive. |
|
| |
Solar panels currently run AU $10 (US $8) per peak watt. Anyone want to run some figures for trees (or algae) in, say, Thailand? |
|
| |
also worth noting that this is much
more environmentally friendly than
burning fossil fuel deposits as it's
converting biocarbon into CO2 which, in
turn, is converted back into biocarbon
when taken up by new plantlife. |
|
| |
However, the calculations here are shot
: even if the 48km by 48km area were
true (which some correspondents have
doubted), you'd surely need that every
year until such time when the first felled
square had regrown to full trees... that,
suddenly, is an awful lot of space. |
|
| |
I presume you mean biocarbon. |
|
| |
With coppicing, you can crop quite frequently. With other, non-tree species, you can get a crop a year or more. Algae you can harvest year round. See [link] for articles about algae. |
|
| |
edited thanks [bunsen] - I have no idea
what bicarbon is... and that's not a call for
a list. |
|
| |
I think it's bad that some people can't wait until Christmas is over before they burn their trees. |
|
| |
//But you are still comparing Joules to Watts//
In this particular case, I actually know what I am talking about. Everything else is just bullshit. I calculated average Power using the time period that the Energy was developed. |
|
| |
109GJ for 10,000m2 in (365*24*60*60) seconds is 0.345W/m2. |
|
| |
Then compared to my estimated annual 24hr average insolation power of 300W, which I ought to confirm but can't be bothered. |
|
| |
BunsenHoneydew, Ah, I misunderstood what you were trying to say.
According to the link (but note the relation to petroleum in the url!), trees for power is not so good. But it is a very well written paper, I think. |
|
| |
[ling] Ah! Ok, we were just comparing things in a different fashion. You were calculating power, I was calculating energy. Neither of us was wrong, we were just calculating different things. |
|
| |
Thanks for the link iron_horse, I see for Thailand the 24hr average is 200W/m2. |
|
| |
You are welcome [Ling], and thanks for posting the idea. We should not blame trees for failing to catch all of the sunlight in an area, unless we subject solar panels to the same scrutiny. Linky says 100 hectare solar farm produces 20 MW at peak, for a peak power of 20 watts per square meter. That makes an annual average power of something much less. |
|
| |
The paper which says that biofuels are not sustainable makes some assumptions that do not have to be true. For example, a biofuel crop that fixes nitrogen into the soil from the air will not deplete the soil like other crops. Black Locust trees are an example. Also, it is possible to design a biofuel plantation with several layers of vegetation that will catch almost all of the sunlight and contribute more value than a mono-culture biofuel crop. |
|
| |
On learning about coppicing I revisited this idea. Only to find the term in the title. I imagine I misread it for codpiece. I wonder how many other things I see, do not understand, but blithely continue on with the rest that makes sense. |
|
| |
//Carbon sequestration is a totally unproven technology with massive risks involved. Besides, we need the -02// |
|
| |
The last statement is incorrect. |
|
| |
From Wikipedia:
Composition of dry atmosphere, by volume: |
|
| |
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
...
Carbon dioxide (CO2) 390 ppmv (0.039%)
...
|
|
| |
(ppmv = parts per million, by volume)
The pre-industrial level of CO2 was apparently around 280ppm. |
|
| |
There's no need to worry about removal of the oxygen alongside the carbon with CO2 sequestration. Dropping the CO2 to pre-industrial levels by sequestration won't make a significant difference to the oxygen level (the oxygen level would be reduced by about one-thousand, nine-hundredth, or 0.053%).
I don't think even sequestering *all* future fossil fuel carbon combustion would be very significant. My estimate for that is 3000 billion tons of CO2 (based on proven reserves in 2005-7). That's 3×10^15 kg, and the Earth's atmosphere is apparently around 5×10^18 kg. Air is about 23% O2 by weight, so let's say 10^18 kg of oxygen. So sequestering all that fossil fuel as CO2 would only remove 0.22% of the oxygen. (The O2 in CO2 is about 73% of the mass.) Even allowing for more fossil fuel to be found, it's not going to be a large proportion of the total O2. |
|
| |
Incidentally, the Earth as a whole is gradually oxidising, because hydrogen escapes to space. The rate is currently very low, but this must still be significant over very long timescales. |
|
| |
I'm not saying carbon sequestration is good or bad, just that being concerned about the oxygen also sequestered is unnecessary. |
|
| |
//...I thought that one output of trees, while growing, was oxygen, so they must be separating carbon from oxygen in some way.// To be precise, the oxygen released by growing plants comes from water, not from carbon dioxide. Not that it changes the overall story. |
|
| |
Kudos to Ling for figuring in (averaged) watts per square metre. Non-standard units like watt-hours per year per square metre are unnecessary and annoying. |
|
| |
//To be precise, the oxygen released by growing
plants comes from water, not from carbon
dioxide. Not that it changes the overall story.// |
|
| |
The oxygen comes from both. The
photosynthetic equation is: |
|
| |
2n CO2 + 2n H2O + photons -> 2(CH2O)n + 2n O2 |
|
| |
As you can see, for every two H2O that
goes in, 2 O2 comes out. Therefore at least half
of the oxygen is coming from CO2, when it is
separated so that the C can bond into the
carbohydrate. |
|
| |
Strangely, what I said is still correct. 4n water molecules are split (releasing 2n oxygen molecules), and 2n water molecules are synthesized, using oxygen derived from CO2. So while your equation is correct (though simplified), the released oxygen does, in fact, come entirely from water. |
|
| |
While I would assume that some oxygen from CO2 ends up being released, it only happens indirectly - via water. |
|
| |
//To be precise, the oxygen released by growing plants comes from water, not from carbon dioxide. Not that it changes the overall story.// |
|
| |
Ha, we're really putting those guys from 2006 straight! |
|
| |
// I wonder how many other things I see, do not
understand, but blithely continue on with the rest that
makes sense. // |
|
| |
Undoubtedly far fewer than [The Alterother] does. |
|
| |
Why has nobody invented the coppiceable pig? |
|
| |
Du Pont developed a prototype in the mid '80s but
the Pigs' Union objected. |
|
| |
I think other genres of music should also be given the benefit of intensive tree burning. |
|
| |