[Le Inc]

Küsimus ei ole teraviljas, võib võtta kasvõi energiavõsa. Fakt on see et energeetika (sealjuures räägime primaarenergiast) seisukohalt me saame rohkem tagasi kui sisse investeeritakse. Kas nüüd see rahalises mõttes otstarbekas ja tasuv on teine küsimus. Raha ja energia tuleb antud juhul üksteisest lahutada.

See euro- või riiklik toetus jms. plära on puhas poliitika. Kui sa saad masuudi MW*h X krooni eest kätte, aga teraviljast aetud piirituse MW*h eest pead X*10 kr maksma, siis loomulikult valitakse esimene tee (pealegi ei kasvatata hetkel otra selleks et seda ahju panna, ikka seleks et hüva kesvamärjukest saaks rüübata). Sellepärast ei kehti ka reegel "põllumees - põline rikas" ... aga kuna tööline rikas on olnud?. Põhiiva on ju selles, et väide nagu päike selle 5..6 kasvukuu juures taime energiat ei salvesta on äärmiselt väär. Seda enam peaks džunglis roheline mass kordi kiiremini kasvama kui meil siin põhjas.

"Tehakse põldudele kahju" ... minu meelest iga samm mida inimene siin Maal teeb on üks suur "kahju" loodusele. Ikka keegi või miski kuskil kannatab kui me kaevandame järjekordse tonni põlevkivi või kui viskame vana arvutirondi prügimäele. Isegi kõige rohelisem roheline tahab -25 C pakasega kodus soojas istuda ja telekat vaadata. Pealegi kui me oleme sunnitud teravilja piiritusega masinaid käitama siis me peaks tegema seda nii palju kordi energiasäästlikumalt kui palju praegu on nafta omahind odavam, kui me tahame säilitada praegust tarbimist. Vähemalt mingi alternatiiv on ja ehk me ei peagi nii pea hobuste juurde tagasi pöörduma ...

[Ho Ho]

[marti252]

[Le Inc]

Kütte saaks lahendada ka puidu, turba, põlevkiviga. Bensiinile alternatiive on raske luua. Arvata on, et rahuldamaks praegusi vajadusi peaks me ka terve Kuu metsaga täitma. Kui kuskilt miskit võtta ei tule lihtsalt uue ajastuga kohaneda.

Ainuke energiamahukas ettevõtmine on 10..14 % alkohooli sisaldavast "leemest" piirituse välja aurustamine. Sealt saaks muidugi jahutusvee energia tagasi ...

[Ho Ho]

[marti252]

Tundub, et kui nii meie disskussioon jätkub, selgitan ma selle 91lk uurimustöö ümber .

Et sa sellest aru saaksid peaksid sa viitsima selle läbi lugeda, siis võiks edasi diskuteerida. no offence

[bezdomn6i]

[Ho Ho]

[marti252]

[Le Inc]

[bezdomn6i]

[Ho Ho]

[Le Inc]

Mida ma pean mõtlema metaanist!? Anna vihjeid

Metaan tekib orgaanilise aine lagunemisel. Lõik konspektist:

[marti252]

[bezdomn6i]

[Le Inc]

[Ho Ho]

[bezdomn6i]

[Le Inc]

Uhh, see oli rohkem põhimõtteline küsimus/väide et loodust kahjustamata saab ju vilju korjata. Kes veel ei tea siis Pääsküla prügimäel toodetakse biogaasi nii mis mühiseb. Lõik konspektist:

[kellu]

Metaanist (mida ma kütteks 20-25m3 ööpäevas ära põletan):
Seal antropogeense ja loodusliku tekke tabel kah. Umbkaudu jaguneb praegu pooleks. Minu arust dzunglit ja vihmametsi Weltandiks ei peeta. Õigupoolest on see vihmametsas metaani mitte tekkimine ka loogiline, vihmametsas toimub ju kõdunemine hapnikudefitsiidita ja seega puuduvad eeldused metaani tekkeks. Kohtades, kus vesi metsa all ja kogu elu lõpetanud orgaaniline materjal vee alla vajub ja sääl kõduneb (või säilib), saab metaan tekkida, nagu meiegi soodes.
Artikkel kasuhoonegaasist annab metaani looduslikuks lagunemisajaks atmosfääris 9-15a.
Ma ei ole leidnud allikaid, mis kirjeldaks atmosfäärilise lagunemise protsesse, põletamisel toimub kõigepealt pürolüüs ja siis alles jääkainete (H2, CO) oksüdeerumine. Kuna metaan on õhust kergem siis toimub lagunemine ilmselt umbes sellisel kõrgusel atmosfääris, kus hapnikupuududst olla ei tohiks ja lagunemise käigus pürolüüsi vaheprodukte alles jääda ei tohiks.

Päris huvitav asi on muide kirjas turvast puudutavas artiklis. Kui üldiselt peetakse turba süsinikuringi pikkuseks 1000-3000 aastat, siis "kultuurturbaraba" puhul on see ainult 100a ja seega tegemist peaaegu loodussõbraliku kütusega. Oluliseks peetakse turbaraba võimet siduda atmosfäärist CO2 ja seda sisuliselt kütusena akumuleerida sama jõudlusega, kui seda teeb sama pindalaga mets...

[Fiocchi]

[kellu]

[marti252]

[Le Inc]

link :: Palju inimene võimsust välja annab!? (arvutage ise)

Primaarenergia vs. primaarenergia ei saa olla mitte mingil juhul väiksem kui sisse paneme (mitte meie, vaid päike). Iseasi kui me hakkame sealt kõrgema taseme energiat tootma (mehaaniline, elektri vms.). Pealegi tuleb siin mängu juba aeg, kas periood on 1 päev või 8760 päeva. Kas see lause:

[bezdomn6i]

[Le Inc]

Krt see on küll viimane post sellel teemal (hulluks võib minna ). See on potentsiaalne energia! Pealegi saaks sellest vast 10 miljoni ameerikalse aastase energiavajaduse ära katta (vägivaldne võrdlus).

* Maakera taimestik suudab aasta jooksul salvestada Päikese poolt saadetud 5,6*10^3 ZJ (zettadžaul 10^21 J) 6,5 Gt*a-1 rohelise (orgaanilise) massina. Siin peaks kaudselt ka väetised jms. kulud sees olema. Muide põllukultuuride kasvatamine võib olla hoopis töömahukam (sealjuures ka energiamahukam) kui lasta loodusel omaviisi käia. Aga samas ega lepa lehti meist ilmselt keegi sööma ei hakka.

Kui me suudaks kas või 0,005% Maale langevast päikese kiirgusest ära kasutada, oleks aastane energiavajadus kaetud.

[Tanel]

[kellu]

[Ho Ho]

Tollest 91lk uurimusest mõned tsitaadid mis tundusid huvipakkuvad:

To satisfy a significant part of the ever-growing automotive fuel and electricity demand in the
world, five billion oven-dried tonnes (5 × 1015g) of biomass would be needed each year for decades
to come. At 10 oven-dried tonnes (odt)/yr-ha of the average29 replaceable dry mass yield from
industrial plantations, this mass of bio-feedstock would require an annual harvest of 1/8 of the
dedicated 500 million hectares of these plantations with the eight-year crop rotation – an area close
to 1/2 of the total area of tropical forest on the earth in 2004. These estimates are not merely a
product of our imagination. A United Nations Bioenergy Primer (Kartha and Larson, 2000) states:
“In the most biomass-intensive scenario, [modernized] biomass energy contributes...by 2050...
aboutone half of total energy demand in developing countries. . . . The IPCC’s30 biomass intensive future
energy supply scenario includes 385 million hectares of biomass energy plantations31 globally in
2050 (equivalent to about one quarter of current planted agricultural area), with three quarters of
this area established in developing countries.”
To maintain a high average yield of biomass over many crop rotations (over, say, 100 years),
industrial tree plantations require: (1) intense mechanical site preparation and weed control with
pre- and post-emergent herbicides; (2) periodic fertilization with macronutrients (N, P, K, Ca, Mg
and S), and micronutrients (Fe, Cu, B, Mn, Mo, Zn, Se, etc.); (3) continuous use of insecticides; and
(4) improved matching of plant genotypes to the plantation sites. For example, in the Jari, Brazil,
plantation (McNabb and Wadouski, 1999), the site preparation involved slashing and burning of
the native forest in 1972; chainsaw fell or drag chain removal of plantation trees, rotary hoeing,
intensive removal of “vegetative competition” by manual weeding and herbicides, and switching to
different tree species several times every 6-10 years.
To increase chances of high biomass production, industrial plantation designers will inevitably
tend to choose the biologically prolific sites in good climate, with seemingly32 rich soil, good water
supply, and easy access (i.e., the ever-receding boundaries of mature tropical forests), rather than
the remote, poor quality habitats with damaged soil and little vegetation. Therefore, the new huge
industrial plantations will negatively impact or destroy some of the most pristine ecosystems on the
earth (this is a statement of fact, not a moral judgement). In effect, the low-entropy environment
in the tropics will be mined, see (Patzek, 2004), just like everywhere else since times immemorial.
In summary, we are discussing here a possibility of the largest industrial forestry project in the
history of mankind. This project would cause the severest ever competition for good-quality land,
impact every ecosystem on the earth, and all humans.

...

The most thorough known to us studies of a terra-firme forest site in Eastern Amazonia were
performed by Mackensen et al. (2000) and Klinge et al. (2004). These studies revealed that
the mean living above-ground phytomass was 257 tonnes/ha, and the mean mass of litter was
14 tonnes/ha. The mass estimate by Mackensen et al. was low when compared with other
published studies. More than 50% of carbon, 20% of total nitrogen, 10% of total phosphorus, and
66-99% of total potassium, calcium and magnesium were locked in the above-ground phytomass.
Consequently, phytomass removal and destruction during forest conversion to a plantation will lead
to major nutrient losses. The nutrient store estimate by Mackensen et al. was medium-to-high
when compared with other published studies. Some of the nutrient losses can be replenished with
synthetic fertilizers, but other cannot, leading to a slow degradation of plantation soil and biomass
productivity.

...

Wood pellets, see Figure 13, are the most valuable product of an industrial wood-for-energy
plantation. They are easy to transport over long distances, relatively safe and easy to store, and
easy to process in an overseas chemical plant.
Large industrial tree plantations are highly mechanized, and require fossil energy to fell trees,
strip branches from tree stems, transport the bark-covered stems from the plantation slopes to
a wood pellet-making facility, produce wood pellets, and transport these pellets to a local port
by truck and train, or barge, and overseas by ship. Fossil energy is also required to mechanically
prepare the plantation sites for each new tree rotation, deliver fertilizers, herbicides and insecticides
to the trees, or remove weeds.
Part of the fossil energy requirement may be satisfied by burning the local “biowaste” (slash,
undergrowth) to produce heat and electricity, thereby stripping the vital nutrients from the soil,
and exacerbating erosion problems. This is the Faustian dilemma44 of industrial forestry: What is
“saved” in “biowaste” must be put back as fertilizers and other measures to fight the ever-growing
rate of soil depletion and erosion. The remaining energy requirement is due to automotive fuel use
in forest machinery and transportation vehicles.

...

The conversion of wet and perishable stemwood/stembark, see Figure 12, to dry, compact and
portable wood pellets, see Figure 13, is the single biggest energy outlay of an industrial biomassfor-
energy plantation. An inefficient facility using the wood “waste” is out of question. Consider
the following example:
Example 1 A wood pellet production facility in New Zealand (Nielsen and Estcourt, 2003) produces
8000 tonnes of pellets per year by using 36 GWh of steam generated from 20 000 tonnes/yr of
“low-quality wood waste” (with the heating value of 6.4 MJ/kg) as heat and electricity. Therefore,
the specific energy requirement to produce wood pellets is

(36 GWh × 3600 s/h)/(8000 tonnes of pellets)= 16 MJ/kg (5)

Thus, the transformation of raw wood into pellets requires 16/20 = 80% of the calorific content
of oven-dry hardwood45! If wood pellets are produced in small quantities as a byproduct of other
industrial processes (paper pulp and timber production), this inefficiency may be tolerated because
there exists genuine “waste” wood. If the large-scale production of wood pellets is the only goal,
then the whole concept breaks immediately down, because 4 kg of the wood must be burned to
produce 1 kg of pellets.

thorough economic analysis of eleven alternative designs of a state-of-the-art pelleting factory
has been performed by Theka and Obernbergera (2004). Because wood leaving the tropical
plantations is wet, we will consider here only their Scenarios 1-6, which require drying of raw
material with 55% of moisture by weight46. The energy costs of chipping tree stems were not
included in the analysis by Theka and Obernbergera (2004), while the energy costs of griding
the chips were partially included.
Our estimate of energy required to chip the raw wood is based on the work by Spinelli and
Hartsough (2001), who estimated that, given the chipper power in kW, and a wood piece mass
in metric tonnes, the time to chip this wood is

tchip = 60 × (0.02 + 13.1/( Piece mass × Power) + 566 / Power)

Here we have assumed that the wood chippers are stationary electrical machines, 250 kW in power,
and the wood pieces are 300 kg on average.
As the wood pelleting facilities of interest here will operate in remote locations in the tropics,
no heat recovery as district heat is included. Also, the assumed 35% efficiency of an electric power
plant may be difficult to achieve in remote conditions; therefore, a 20% efficient electric power
plant is also considered, see Table 12. The results for the more efficient power plant are shown in
Figure 14. The average of all scenarios involving 55%-wet raw wood is 6.4 MJ of primary energy
per kilogram of 10%-wet pellets. For the lower power plant efficiency, the resulting average primary
energy requirement is 8.1 MJ/kg of pellets.
Remark 12 A highly-efficient conversion of 55%-wet raw wood to 10%-wet wood pellets requires
on average 33 – 41% of the gross calorific value of oven-dried wood. This conversion will be carried
out in a central, state-of-the-art facility, capable of producing 20 000 – 60 000 tonnes of pellets per
year. If “wood waste” from tree plantations were used to power this facility (the most probable
scenario), additional fertilizer use and other soil conservation measures would have to ensue.
Parenthetically, the energy cost of converting raw wet wood into portable pellets is comparable
to the energy dissipated on fermenting aqueous glucose to a beer with 8% ethanol by weight.
However, the wood pellets are a high quality fuel or feedstock, while the 8% beer needs a lot more
heat to separate the remaining 92% of water from the ethanol.

...

In terms of useful shaft work, wood conversion to ethanol is by far the poorest of the three alternatives
presented here, and we shall provide only an approximate conversion efficiency. Ethanol
is obtained from enzymatically converting wood48 cellulose (45% by weight) into glucose, wood
hemicellulose (30% by weight) to xylose, and fermenting both sugars to 8-10% industrial beer.
This beer is then distilled to 96% ethanol using 19 MJ/kg ethanol in fossil fuels, and the remaining
water is excluded in molecular sieves (Patzek, 2004). The respective conversion efficiencies,
assumed after Badger (2002), are listed in Table 13.
Therefore, from 1 kg of 10%-wet pellets, one may obtain 0.9×(0.131+0.069) = 0.18 kg of 100%
ethanol at the fossil energy expense of 3.4 MJ to distill the beer plus more energy and chemicals to
process the wood. For simplicity, we will assume that the remaining 0.23 kg of lignin in the wood
pellets will deliver the necessary 3.5 MJ of heat. The chemical exergy of the produced ethanol
is (Patzek, 2004) 29.65 × 0.18 = 5.33 MJ/kg pellets. If this ethanol is then burned to power a
35%-efficient car, 1.87 MJ/kg pellets is obtained as shaft work.



Gigantic tree plantations could be designed to replace, say, 10% of the fossil energy used globally
every year for 40-80 years. About 500 million hectares (a little more that 1/2 of the United States
area) of new plantations would be needed. These plantations would be implemented in the tropics
in good climate with plentiful water supply, apparently good soil, and easy access, i.e., along
the ever-receding edges of natural tropical forests and along major rivers. Talk about developing
industrial tree plantations for profit in degraded and sterile environments does not seem practical
or convincing. Therefore, the new biomass-for-energy plantations will impact disproportionately
many of the most important ecosystems on land and in shallow sea water. Will the global damage
of tropical forest and clean water sources be beneficial in terms of saving other earth resources?
The answer based on the work presented in this paper is a decisive no. In order to be profitable, a
biomass-for-energy plantation must achieve a consistently high yield of dry wood mass. Trees that
grow fast (e.g., Acacia mangium) use more water and nutrients than the slower-growing species.
Consequently, these fast-growing trees damage soil and their wood is excessively wet after harvest.

We find that sustainable generation of electricity and/or Fischer-Tropsch (FT) diesel fuel
from wood pellets produced in remote tropical plantations is impossible, unless sun-drying of raw
wood and improved soil management are widely implemented. In our opinion, the scale and rate
of wood processing necessary to replace a substantial fraction of automotive fuel and electricity
demand on the earth makes the widespread sun-drying of wood impractical or impossible.

The gigantic tropical sugarcane plantations on mostly agricultural land suffer from the similar
weaknesses. Their shaft work output from burning cane-ethanol in the efficient internal combustion
engines is insufficient to cover the cumulative free energy consumption in producing this ethanol.
The only option that gives a marginal benefit is the conversion of the sugarcane ethanol to hydrogen
used in 60%-efficient fuel cells to produce electricity (Deluga et al., 2004), but such cells do not
exist, see Appendix A.

In general
1. Biomass-for-energy plantations are environmentally costly and inefficient engineered systems,
and their long-term high yields are uncertain and questionable.
2. Locally-produced electricity from biomass seems to be the best option that could make a
prolific acacia and sugarcane plantation “sustainable,” if their immediate environments were
not degraded by the toxic ash and air emissions.
3. The Fischer-Tropsch automotive fuel from biomass is not as good an option, and the
plantations producing it are not sustainable.
4. Ethanol from tree biomass seems to be an especially poor choice.
5. The anhydrous ethanol automotive fuel from sugarcane stems is a better option, yet it is
unsustainable too, even when burned in efficient hybrid cars.
6. Plant residues, called “trash” by those who do not understand their vital importance to
the long-term survival of plantation soils, should be kept on the plantations and allowed to
decompose.
7. Plant “trash” cannot be a significant source of biofuels, and it is not independent of parent
ecosystems.

In particular, for the tree plantations, we reiterate the following:
1. The most desirable product of dedicated industrial tree-for-energy plantations may be wood
pellets produced in very efficient central facilities close to the plantations. Production of these
pellets requires 33-41% of the high heating value of the wood.
2. Excellent site characterization by Mackensen et al. (1999; 2000; 2003), enabled us to use
two average stands of acacias and eucalypts in a freshly established, prolific plantation in
Indonesia as the examples of generic industrial tree plantations in the tropics.
3. Our example acacia and eucalypt stands were the first tree rotations, and received small
fertilizer treatments of 100 kg NPK/ha. The plantation trees were mostly depleting the
initial store of nutrients in the plantation soil, i.e., the environmental low entropy (Georgescu-
Roegen, 1971; Patzek, 2004).
4. We have calculated the minimum restoration work of nonrenewable natural resources depleted
by the example tree stands, and compared it with the maximum useful work obtained from
the plantation wood pellets as (a) electricity generated in an efficient power station, the
FT diesel fuel burned in a 35%-efficient car plus cogeneration electricity, and (c) wood-ethanol
burned in a similarly efficient car.
5. If this useful work is larger than the minimum restoration work, the example stands are
“sustainable” under our assumptions, otherwise they are not.
6. To calculate the long-term restoration work, we have assumed fertilizer treatments equal to
the amounts of soil nutrients (N, P, K, Ca, and Mg) depleted during a single tree rotation
and site preparation that follows each harvest.
7. We have assumed that fertilizer application efficiency is 100%, i.e., 30-90% of the various
nutrients are provided by natural (management-independent) fluxes.
8. We have neglected the cumulative exergy consumption in sea transport of wood pellets and
their storage costs.
9. Under the conservative assumptions in this paper, it is possible to show that even an exceptionally
prolific stand of Acacia mangium (22 odt/ha-yr), see Figure 5, is not “sustainable”
with respect to Options (a) and above, unless the cumulative exergy consumption in wood
drying and chipping is cut in half. In view of Item 1 above this cannot be done, unless sundrying
of raw wood is employed, which in turn may be impossible when wood is processed at
a very high rate.
10. Conversion of acacia wood pellets to ethanol that powers the same efficient car, Option (c),
is never sustainable.
11. The example stand of Eucalyptus deglupta is not “sustainable” with respect to Options (a)-
(c), with or without sun-drying of wood, because its net productivity is only 5 odt/ha-yr,
close to the average productivity of tropical forests, see Figure 5.
12. After several tree rotations, the progressively damaged soil may not support the consistently
high biomass yields from the two tree stands.
13. In the long run, therefore, increased fertilizer, herbicide, and insecticide treatments are inevitable,
and their inherent high exergy costs and negative environmental impacts will increase
the degree of unsustainability of these two stands.
14. Plantation management and average biomass yield are highly site-specific, and it is difficult
to make sweeping generalizations from an analysis of the two example tree stands.
For the sugarcane plantations we conclude that
1. An average sugarcane plantation in Brazil is as efficient in sequestering solar energy as the
prolific acacia plantation (all acacia slash must be left on the plantation to decompose, but
only some sugarcane slash is left), and its maintenance costs a little more free energy than
that of the acacias.
2. Ethanol production from sugarcane is driven by burning the cane leftovers, bagasse and parts
of attached cane tops, and converting their heat of combustion to steam, electricity and shaft
work. Sugarcane stem crushing, juice extraction and fermentation, and ethanol distillation
consume almost exactly the same free energy as wood pellets from the acacia stems and bark.
3. We have calculated the free energy consumed to clean the sugarcane distillery wastewater; it
is non-negligible, and requires extra fossil fuel and grid electricity.
4. Despite efficient sequestration of solar energy, the prolific sugarcane-for-ethanol plantation in
Brazil is not sustainable according to our strict criteria, unless its ethanol powers 60%-efficient
fuel cells. The problem is that such cells do not exist, see Appendix A.
5. The sugarcane slash and attached tops sequester a significant amount of solar energy, and
deplete significant amounts of nutrients from the soil. The attached tops and leaves are
burned in the distillery. The detached leaves and slash should be left to decompose and
improve structure of the plantation soil.



Post sai meeletult pikk kuid loodetavasti te ei pahanda.
Kokkuvõttest peaks selge olema et autokütust ei ole võimalik orgaanikast toodetavaga asendada. Hädapärast saaks ainult ehitada kohalikke biomassil töötavaid elektrijaamu.

[edit]

ja muudan posti veelgi pikemaks
kütuseelemendil töötavast autost siis nii palju:
A Efficiency of a Fuel Cell System
In their Science paper, Deluga et al. (2004) claim the following:
. . . Further, combustion used for transportation has 20% efficiency as compared
with up to 60% efficiency for a fuel cell. . .The efficiency of these processes for a fuel cell
suggests that it may be possible to capture >50% of the energy from photosynthesis
as electricity in an economical chemical process that can be operated at large or small
scales. (p. 996).
Following Deluga et al., Patzek (2004) used 60% as an estimate of the overall efficiency of
a hydrogen fuel-cell car. Even this optimistic estimate could not make the industrial corn-ethanol
cycle sustainable to within a factor of two. Not so with sugarcane ethanol. It might be called
somewhat sustainable if the path from the ethanol to electric shaft work were 60% efficient.
First, we assume that the cane ethanol-water mixture used to generate hydrogen is analytically
pure C2H5OH and H2O. Thus, there are no other contaminants to poison65 the delicate catalyst that
will convert this EtOH-H2O mixture to hydrogen, carbon dioxide and carbon monoxide (Deluga
et al., 2004). The catalyst is made of a rare-earth metal, rhodium66, and a Lanthanoid, cerium67.
The catalytic reaction is claimed to have 100% selectivity and >95% conversion efficiency. We
assume the conversion efficiency n1 = 0.96.
After Bossel (Bossel, 2003), we summarize efficiency of a Proton Exchange Membrane (PEM)
fuel cell as follows. In fuel cells, gaseous hydrogen is combined with oxygen to water. This process
is the reversal of the electrolysis of liquid water and should provide an open circuit voltage of 1.23
V (Volts) per cell. Because of polarization losses at the electrode interfaces the maximum voltage
observed for PEM fuel cells is between 0.95 and 1.0 V. Under operating conditions the voltage is
further reduced by ohmic resistance within the cell. A common fuel cell design voltage is 0.7 V.
The mean cell voltage of 0.75 V may be representative for standard driving cycles. Consequently,
the average energy released by reaction of a single hydrogen molecule is equivalent to the product
of the charge current of two electrons and the actual voltage of only 0.75 V instead of the 1.48 V
corresponding to the hydrogen high heating value68. Therefore, in automotive applications, PEM
fuel cells may reach mean voltage efficiencies of

n2 =(0.75 V)/(1.48 V)= 0.50

However, there are more losses to be considered. The fuel cell systems consume part of the generated
electricity. Typically, automotive PEM fuel cells consume 10% or more of the rated stack power
output to provide power to pumps, blowers, heaters, controllers, etc. At low power demand the fuel
cell efficiency is improved, while the relative parasitic losses increase. The small-load advantages
are lost by increasing parasitic losses. Let us assume optimistically that for all driving conditions
the net power output of an automotive PEM fuel cell system is about n3 = 0.9 of the power output
of the fuel cell stack.
Depending on the chosen drive train technology, the DC power is converted to frequencymodulated
AC or to voltage-adjusted DC, before motors can provide motion for the wheels. Energy
is always lost in the electric system between fuel cell and wheels. The overall electrical efficiency
of the electric drive train can hardly be better than n4 = 0.9.
By multiplying the efficiency estimates, one obtains for the maximum possible tank-to-wheel
efficiency of a hydrogen fuel cell vehicle

n = n1n2n3n4 = 0.96 × 0.50 × 0.90 × 0.90 = 0.38, (11)

or 38%. This optimistic estimate agrees exactly with another analysis (31-39%) (Fleischer and
Ørtel, 2003), and is significantly less than the 60% used by the promoters of a hydrogen economy
and hydrogen fuel cell vehicles.

Ehk siis kütuseelement pole midagi nii säästlik kui reklaamitakse

[bezdomn6i]

[Ho Ho]

Lisaks veel eelnevale jutule et minu mäletamist mööda saab fossiilsete kütuste kasutamisel tagasi ~50x rohkem energiat kui kulub nende kaevandamiseks. Eespool tsiteeritud uurimusest järeldub et parimal juhul saab biomassist tagasi 20% ehk 0.2x "rohkem".
Ehk siis ühe ühiku energiahulga saamiseks tuleb biomassi energiat kasutades kulutada ~250x rohkem energiat kui fossiilkütuseid kasutades.

[NuCleo]

[Le Inc]

Ho Ho tubli et viitsisid mõned tabavad lõigud välja tuua. Kohe jäid silma suhteliselt mõttetud energiat raiskavad "protseduurid".

Milleks teha puidu massist pelleteid? See on ju vana nali et pelletite (k.a. briketi pressimine turbast) on meeletult energiat raiskav! Lihtsam on puu ära hakkida ja seejärel kas katlasse pihustada või piiritust ajada. Kindlalt 80% kadu kahaneks, ehk 30..40% peale. Kas ma saan õieti aru et ta kasutab piirituse kütteväärtusena 19 MJ/kg (peaks 29 MJ/kg olema)? Siiski destilleerimine on energiamahukas.

Tänapäeval ei tehta ühtegi keskmist või suuremat biomassil toimivat elektrijaama ilma jahutusvee realiseerimise võimaluseta. 30% on jah elektriline efektiivsus, aga 80..90% on võimalik saavutada ka jahutusvee ära kasutamisega (metsakuiv puu pole ka probleem, hiljem saab niiskuse kondensaatoritega kinni püüda). Sama lugu on ka destillatsiooni juures, kus jahutusvee saaks ära kasutada.

Kui sul ikka on kitsas käes siis tehakse kõik et viimnegi piisk läheks asja ette. Tundub et selle töö on miskine naftamagnaat tellinud ...

[marti252]

[Fiocchi]

[Ho Ho]

[Le Inc]

[namstoop]

Põlevkivist on otsas kolmandik. Nii et jah, 2 miljardit tonni on veel kasutamiseks olemas, 1 miljard sai just hiljuti täis.

[Scart]

[Ho Ho]

Põlevkivi koha pealt veel nii palju et kas mitte suur osa sellest ei asu asustatud piirkondade all ning sell kätte saamiseks peaks suht palju inimesi kusagile mujale elama saatma?

Võibolla ma mäletan asju valesti, fosforiidisõdade ajal olin alles koolieelik

[Le Inc]

Igatahes see vana kes telekas 1 miljardindast tonnist putras, rääkis veel 2 miljardist kaevandatavast põlevkivi tonnist. Ju ta siis mõtles ikka seda mida hõlbus kätte on saada.

[Zajats]

Meil on kõige reaalsem teha väiksed tuumarektorid. Uraani on meil kõrini, tuleb ainult kaevandada. Tänapäeval on tehnoloogia juba nii turvaline et pole ohtlik.

[gemini]

[stepzter]

[Elof]

[gemini]

TanElofJ, mõtled termotuumareaktoreid? Mis töötavad raskevesinikul?

[aht5]

Siiani on juttu olnud ainult loodust säästlikumatest transpordiviisidest http://www.greencarcongress.com/2006/01/beluga_shipping.html http://www.gizmag.co.uk/go/3692/ ja energiaallikatest http://www.gizmag.co.uk/go/5136/ aga olulisel kohal energia tarbimises on ka majade soojapidavus.

[Ho Ho]

[Scart]

[marti252]

link :: Rainer Nõlvak: Roheline Energiakava 2020

Lugege läbi ja tegutsema:wink:

Päris huvitav pilt Venemaa plaanidest torujuhtmete ehitamisel
http://www.eia.doe.gov/emeu/cabs/Russia/images/fsu_energymap.pdf