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Published online 10 October 2007 | Nature 449, 652-655 (2007) | doi:10.1038/449652a
News Feature
Biofuel: The little shrub that
could - maybe
India, like many countries, has high hopes for jatropha as a biofuel source, but
little is known about how to make it a successful crop. Daemon Fairless digs for
the roots of a new enthusiasm.
Daemon Fairless
STRINGER INDIA/REUTERS
With a top speed of about 110 kilometres an hour, India's Shatabdi Express is not
much to brag about by the standards of a French TGV or a Japanese Shinkansen
train. Nonetheless, as the stock for one of the country's fastest and most
luxurious passenger lines, the Shatabdi trains have a certain prestige. So when,
on New Year's Eve 2002, the Shatabdi train from New Delhi to Amritsar was
powered in part with biodiesel for the first time, it was a clear statement of the
government's desire to wean India off imported petroleum.
Diesel is India's main liquid fuel: the country burns roughly 44 million tonnes, or
320 million barrels, of the stuff a year, as opposed to about 94 million barrels of
gasoline. The trains account for a significant part of that. Kunj Mittal, who heads
the government-operated rail service's engineering and traction division, says its
fleet of 4,000 engines currently burns about 1.7 million tonnes a year, and that
he wants to replace at least 10% of that with biodiesel at some unspecified point
in the future. But he would need 200 million litres of biodiesel a year. Which is a
problem. “At this stage,” says Mittal, “there is no mass production of biodiesel.”
Like many others around India, the rail service is looking to an unprepossessing,
poisonous scrub weed to try to do something about that. It has planted a million
Jatropha curcas seedlings on unused land along its tracks and elsewhere. It's just
one symptom of the jatropha fever that is spreading around the country and the
world — to the slight bewilderment of some of the scientists who best understand
the shrub.
Jatropha, a member of the euphorbia family, originated in Central America. It has
long been used around the world as a source of lamp oil and soap, and also as a
hedging plant. One of its great selling points as a biofuel is the fact that growing
it need not compete with the cultivation of food. Of 306 million hectares of land
considered in a report by India's Ministry of Rural Development, 173 million are
already under cultivation but the rest is classified as either eroded farmland or
non-arable wasteland. That's the sort of land that jatropha can thrive on, with
bushes living up to 50 years, fruiting annually for more than 30 years and
weathering droughts with aplomb1. In the early 2000s then-president A. P. J.
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Abdul Kalam repeatedly endorsed the plant for its potential contributions to
energy security and as a route to greening barren land. Jatropha has been held to
promise a reliable source of income for India's poor rural farmers and energy selfsufficiency for small communities — all while reducing fossil-fuel greenhouse-gas
emissions and soil erosion.
Oasis in the desert: jatropha
cultivation can halt soil erosion, increase water storage in the soil and
transform barren expanses into lush, productive land.J. CHIKARA
In 2003, India's Planning Commission recommended a national mission on biofuel,
a two-phase project for wide-spread cultivation of jatropha on wasteland across
much of India. The first phase of the mission aims for 500,000 hectares of
jatropha grown on government land across the country. The biodiesel would be
produced primarily by panchayats — local governing bodies — at the village level,
coordinated at the national level by a consortium of government departments.
Should the first phase go according to plan, India's central government would
embark on the second phase of the mission — planting a total of 12 million
hectares of the plant and privatizing the production of jatropha biodiesel.
Although it seems likely to go ahead eventually, various ministerial meetings that
might have given the national mission on biofuel the seal of approval have been
postponed in favour of higher-priority issues. Despite this, several states have
enthusiastically hopped aboard the jatropha express, providing free plants to
small-scale farmers, encouraging private investment in jatropha plantations and
setting up biodiesel processing plants. The Ministry of Rural Development, which
is set to coordinate the national mission on biofuel when it is approved, estimates
that there are already between 500,000 and 600,000 hectares of jatropha
growing across the country.
And India is not alone in its hopes for the shrub. In February 2007 China, which
claims to have 2 million hectares of jatropha already under cultivation, announced
plans to plant an additional 11 million hectares across its southern states by 2010.
Neighbouring Myanmar (Burma) has plans to plant several million hectares; and
the Philippines, as well as several African countries, have initiated large-scale
plantations of their own. India looks forward to encouraging more such schemes
and quite possibly profiting from them. “Once we have an operational programme
and have something to offer the world,” says Krishna Chopra, the recently retired
principal adviser to India's Ministry of New and Renewable Energy, “I think
exporting the know-how would certainly be one of the first areas to develop.”
The great unknown
Although there is reason to be enthusiastic about jatropha's potential as a
biodiesel feedstock in India and beyond, there is one rather sobering concern:
despite the fact that jatropha grows abundantly in the wild, it has never really
been domesticated. Its yield is not predictable; the conditions that best suit its
growth are not well defined and the potential environmental impacts of largescale cultivation are not understood at all. “Without understanding the basic
agronomics, a premature push to cultivate jatropha could lead to very
unproductive agriculture,” says Pushpito Ghosh, who has been working on the
plant for the best part of a decade, and who is now director of the Central Salt
and Marine Chemicals Research Institute (CSMCRI) in Bhavnagar.
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When Ghosh first arrived at the CSMCRI, the United Nations Development
Programme (UNDP) had already given the institute funding for the cultivation of a
modest jatropha plantation, although not for biofuels work. The idea was to see
“how to make use of waste land, coastal areas and sand dunes”, Ghosh says.
The plantation started off as an unirrigated, unfertilized, 20-hectare patch of
exhausted scrub: Ghosh wasn't particularly impressed when he first saw it.
“There were shrubs and they were growing,” he recalls, “but it didn't look to me
that it had what was required to make a successful plantation. 'Where are the
seeds?' I said to myself. I didn't see too many of them. Merely planting and
letting jatropha grow doesn't necessarily lead to productive growth.” Nonetheless,
the fact that jatropha lived up to its reputation as a shrub that could eke out a
living on relatively barren land piqued the interest of India's Department of
Biotechnology, which provided a little further funding for exploration of biofuel
possibilities using cuttings from three of the most productive plants in the UNDP
trial.
The seedlings were planted in small plots spread over patches of degraded,
untended land in the eastern state of Orrisa. “The results were not outstanding,”
says Ghosh, “but they were consistent.” Several plants yielded around 1.5
kilograms of seed, enough for about 0.4 litres of diesel. As modest as the results
were, says Ghosh, they created a lot of interest. “For the first time,” he says, “we
were doing something in a systematic way.”
The CSMCRI's work also caught the imagination of Klaus Becker, who arrived at
the institute in 2000 as a visiting agricultural scientist from the University of
Hohenheim in Germany. The original UNDP plot inspired him far more than it had
the sanguine, measured Ghosh. “I saw all this green in what is otherwise a
complete desert. There was absolutely nothing else around it. 'Look,' I told Ghosh,
'if you get this working, you'll be the first in the world'.”
From seed to oil
Becker returned to Germany and set about fund-raising. By 2003 he had cobbled
together a €1.7-million (US$1.9-million) research fund comprised of grants from
DaimlerChrysler, the German Investment and Development Company in Cologne,
India's Council of Scientific and Industrial Research and the University of
Hohenheim. With these funds, Ghosh and his team — working in collaboration
with Becker and scientists at DaimlerChrysler — began exploring the
transesterification needed to turn jatropha into biodiesel. The process had already
been established by Nicaraguan researchers during the 1990s2 and it wasn't long
before Ghosh and his team were producing small batches.
“You could tell simply by looking at it that it was fairly good quality,” says Ghosh
of their first attempts. Chemists at DaimlerChrysler's Stuttgart labs analysed it in
more detail than the CSMCRI was able to and judged it easily good enough to
meet European standards. Further tests at the Austrian Biofuels Institute (ABI),
which pitted the CSMCRI's jatropha biodiesel against fuels from other feedstocks,
showed that it “clearly outperformed biodiesel from rapeseed, sunflower and soya
bean oil in [its lack of a propensity to oxidize],” says the ABI's Werner Körbitz,
adding that the fuel “showed a fully satisfying performance concerning power,
efficiency and emissions”.
Ghosh's vision — and part of the CSMCRI's mandate — was to create a version of
this transesterification process that was both inexpensive and easily replicable at
the village level. Nearly 80,000 of India's 600,000 villages currently have no
access to fuel or electricity — in part because there isn't enough fuel for a fuel
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distribution network. “If people can grow oil directly in villages and produce
biofuels themselves in decentralized plants,” says Ghosh, “then they can achieve
energy self-sufficiency. My colleagues and I are deeply committed to this
principle.”
“The constant urge to simplify and to ensure that every gram of jatropha is
turned into something valuable was a tremendous motivator,” he says, looking
back at the project. But while he and his colleagues were still congratulating
themselves on a job well done, the Times of India ran a story announcing that
DaimlerChrysler was set to test two of its Mercedes C-Class cars on a 6,000kilometre road test across the length and breadth of India using the CSMCRI's
jatropha biodiesel.
Up the Khardungla pass
It was the first Ghosh had heard of it. “Our focus all along has been biodiesel as a
fuel for village folk,” he says, “not for fancy urban folk.” And on top of that there
was an obvious practical difficulty. Up to this point, Ghosh and his team had only
ever produced a few litres of it at a time: you can't get across India on that.
Within a few months, though, Ghosh's team had developed a transesterification
unit capable of producing about 250 litres a day — adequate for use in villages
and small-scale industry3. The Mercedes ran entirely on 100% jatropha biodiesel
from this unit throughout April and May 2004 without any significant engine
modifications. In the summer of 2005, DaimlerChrysler had several automotive
journalists take the cars on a high-altitude test through the Himalayas, including
Khardungla pass, which, at 5,359 metres above sea level, is one of the world's
highest motorable roads.
Pushpito Ghosh tops up a vehicle that
has covered 48,000 kilometres powered only by jatropha biodiesel.S. L.
PUROHIT
While Ghosh and his colleagues were making sure that jatropha could be
processed as a reliable source of biodiesel, several of India's state governments
were busy promoting their own jatropha cultivation campaigns. The state of
Chhattisgarh, which has the most well-developed biodiesel programme in the
country, has distributed 380 million jatropha seedlings to farmers, free of charge,
over the past 3 years, enough to cover 150,000 hectares with the shrub.
Shailendra Shukla, executive director of the Chhattisgarh Biofuel Development
Authority (CDBA), says the state has also provided 80 oil presses to various
village panchayats, and guarantees to buy back jatropha seeds — which have to
be hand-picked off the shrubs — at 6.5 rupees (about US$0.16) per kilogram in
order to stimulate confidence in the crop. Several local businesses have popped
up across the state, says Shukla, that are now operating micro-refineries. “These
are small businesses that provide biodiesel for the use in tractors, irrigation
pumps, jeeps and village power generators.”
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Ghosh says that the CSMCRI has received an order for a refinery from the
country's Defence Research and Development Organisation, part of India's
Ministry of Defence. He explains that the unit would be capable of producing
about 1,000 litres a day and would cost about 14 million rupees to install. In such
a plant, he says, each litre of biodiesel would have a net production cost of about
26 rupees if the seed pods are bought at 6 rupees per kilogram and every scrap
of seed and seed pod is converted into something valuable, with the seed going
into oil, the bi-product seed cake into fertilizer and the seed husk into a highdensity brick that can be burnt for fuel.
The wide governmental support has also attracted substantial business interest.
D1 Oils, a UK-based biodiesel producer, is the world's largest commercial jatropha
cultivator, responsible for around 81,000 hectares of jatropha in Chhattisgarh and
in the southern state of Tamil Nadu, with plans for an additional 350,000 hectares
over the next few years. “The entire programme revolves around the
government-funded jatropha seeds,” says Sarju Singh, until recently managing
director of D1 Oils India. “The government gives farmers free or subsidized
seedlings and D1 Oils guarantees to purchase the seeds at the price prescribed by
the state.” The company claims to have invested more than £3 million (US$6
million) in plant science and financing its share of the plantings, which are joint
ventures.
Cautious approach
Jatropha is already under cultivation in
Tamil Nadu, India, where it can be grown with other crops such as
sunflowers.G. JAWORSKY
Source: United Nations Development
Programme/World Bank. Jatropha figure from Indian Planning Commission
Yet most of these plantings have yet to reach whatever maximum level of
productivity they might eventually attain — the plants need a few years to bed in.
And Ghosh is wary of subsidizing jatropha too much before mass cultivation of
the plant is fully understood. “A lot of government funds may go down the tube,”
he warns. Ghosh doesn't want the farmers to take on too much risk, so he is
suggesting that they intersperse jatropha between their current crops, rather
than banking on it as a cash crop. Shukla has similar reservations. “My immediate
concern,” he says, “is that because the seeds are derived from wild plants there
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is no assurance of yield.” Shukla says the CBDA, like Ghosh, is promoting
jatropha as something farmers limit themselves to planting between their rice
fields. The only situation where all are agreed that it makes sense for small
farmers to cultivate whole fields of jatropha is on farm land that has become or is
becoming unproductive. It is a good fallow crop, says Becker: “It has a deep root
system which stops ground erosion and increases water storage in the soil.” This,
he says, leads in turn “to more biomass growth and an accumulation of organic
carbon in the soil”.
Henk Joos, D1 Oils' director of plant science and agronomy, agrees that assured
yields and the techniques needed to achieve them on a large scale need a lot
more research. Yield estimates currently vary a great deal. India's Planning
Commission estimates about 1,300 litres of oil per hectare, but Ghosh,
conservatively, foresees a figure of about half that. Yield research is the main
focus of D1 Oils' Indian operations, he says. The company is currently testing a
number of jatropha varieties to see which ones grow best in India's varied
climatic zones. “It will be two or three years before we get real scientific data to
base an industry on,” he says. “We are not there yet, we have a lot of work to
do.”
This is the sort of work Ghosh is currently overseeing at the CSMCRI's test plots.
“It isn't the most glamorous work, but the mass multiplication of reliably
producing plants is key to developing an industry, he says. Ghosh and his team
are looking at precisely what kind of soil conditions and just how much water
jatropha needs in order to reliably pump out oil-bearing seeds. The fact that
jatropha plants can survive droughts does not mean they will not be more
productive if they get more water. The optimum amount of water is still unknown.
STRINGER INDIA/REUTERS
The team is also continuously on the lookout for plants that could be potential
progenitors for a generation of a high-yield crop. “We have one plant which has
given us 5 kilograms of seed,” says Ghosh. “We have yet to get that from any
other plant.” The CSMCRI is trying to perfect the use of shoot-tip cuttings as a
means for mass-replication of jatropha plants so it can capture their best
attributes. Culturing tissue cuttings from the plant's growing tip, says Ghosh, is
the most reliable means of propagating exact copies of a parent plant, an
important step in creating an army of dependable high-yield clones. It's a
common enough technique — but like so much technology, it hasn't yet been
reliably adapted to jatropha. “The problem is, we just don't have the protocol
right,” says Ghosh.
These various efforts are not part of any overarching plan. Despite the general
enthusiasm for India's national mission on biofuel, there is a definite lack of
cohesion at the national level. “Right now, ad-hoc research is being done by
different agencies,” says Chopra, “but it doesn't add up, because they each do
their own thing.” A national biofuel policy that was written by Chopra and his
colleagues shortly before his retirement might help. It envisages an authority that
would coordinate research and provide funding through various government
agencies in order to cultivate jatropha on an industrial scale. But this policy, like
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the national mission on biofuel, has yet to go through the cabinet. In this case, it
has been stalled by disagreements between various ministries on how to price
jatropha — the Ministry of New and Renewable Energy suggests subsidizing seeds;
other government ministries suggest subsidizing biodiesel itself. But, says Chopra,
“I expect it will come together, perhaps this year or early next year”.
Ghosh remains cautious and optimistic in level-headedly equal measure. “We
must neither get carried away by hype nor get despondent if the initial results of
cultivation are not as per expectation,” he says. “The future will depend on how
seriously and scientifically we pursue our goals.”
See Editorial, page 637. . Daemon Fairless is this year's winner of the IDRCNature fellowship.

References
1.
Francis, G., Edinger, R. & Becker, K. Nat. Res. Forum 29, 12–24
(2005). | ISI |
2.
Foidl, N., Foidl, G., Sanchez, M., Mittelbach, M. & Hackel, S. Bioresource
Technol. 58, 77–82 (1996). | Article | ISI | ChemPort |
3.
Ghosh, A. et al. Int. J. Environ. Stud. — special issue on India's future
energy options (in the press).
Comments
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
Jatrophraud. Those hyping this species rarely give its common English names
(vomit nut or purge nut) nor those of its oil (hell oil or oleum infernale). It has surface
irritants, yet must be hand picked and dried and the nuts removed by hand from the
outer coating. Its pollen is allergenic, it contains a protein curcin (similar to ricin- and as
with castor beans, eating not too many seeds is lethal), and its oil has some pretty awful
components. Most of the problems could be rectified transgenically. While there is no
regulatory scrutiny of the dangerous wild type being cultivated, the regulatory costs to
render it safer and easier to cultivate would be prohibitive. The rural poor will not be
richer from growing an unmodified, undomesticated crop such as this, they will just be
less healthy. Jonathan Gressel
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10 Oct, 2007
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Posted by: Jonathan Gressel
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
Gressel you are the fraud. I wonder if perhaps you can speak of your years of field
experience or the 71.38% reduction in carbon emissions from the jatrobased biodiesel
BA100. Or the Millions of Rupees now going into the hands of farmers instead of OPEC's
greedy little hands. I have seen this and so much more with my own eyes using non-GM
crops in India and Indonesia. Yes, if you drink it you will get sick its feedstock for biofuel
what do you expect. The road to solving global warming will be beset upon all sides with
people that want to stand on there soapbox and pronounce it all a hoax. Without a shred
of any real credability or experience. If anyone would like to see photographs, facts or
figures from my research please e-mail me. tyson@diplomats.com
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10 Oct, 2007
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Posted by: Tyson Bennett

The reader is invited to official and peer-reviewed sources to ascertain the toxicity
of Jatropha. The oil was initially claimed to contain a fatty acid curcanoleic acid,
structurally and functionally related to ricinoleic and crotonoleic acids, and like them, is a
of skin tumors 1. The irritant/cancer potentiator/synergist seed oil is now known to
contain 0.03 and 3.4% curcusones, irritant diterpenoid phorbol esters. The best
extraction procedures available for the removal of the phorbol esters remove about half 2,
which is unacceptable toxicologically in accessions with high initial content. As jatropha
seeds have a pleasant taste, the plants are particularly attractive to children 1, possibly
because the seeds contain dulcitol and sucrose 3. Numerous cases of toxicoses from the
toxicalbumin lectin (curcin) are reported in the medical literature and ingesting four seeds
can be toxic to a child, with symptoms resembling organophosphate insecticide
intoxication, yet with no known antidote for the lethal mixture 1. Some selections have
been performed to find accessions that are less poisonous. The results are still quite
poisonous, probably because the screening was performed to assay amounts of a single
poisonous component, forgetting that jatropha contains a suite of toxic compounds. For
example, a “non-toxic� Mexican variety has 5% the amount phorbol esters, but
still has half the amount of toxic lectins as the toxic varieties, and about 25% more
trypsin inhibitors and 50% more saponins 4. The poisons could all be removed using RNAi
technology, and the meal would then be appropriate for animal feed, and not as a
dangerous environmental pollutatnt. 1. INCHEM. Jatropha curcas L. Intl. Programme
Chem. Safety http://www.inchem.org/documents/pims/plant/jcurc.htm (1994). 2. Haas,
W. & Mittelbach, M. Detoxification experiments with the seed oil from Jatropha curcas L.
Industrial Crops and Products 12, 111-118 (2000). 3. Gübitz, G. M., Mittelbach, M. &
Trabi, M. Exploitation of the tropical oil seed plant Jatropha curcas L. Bioresource
Technology 67, 73-82 (1999). 4. Makkar, H. P. S., Aderibigbe, A. O. & Becker, K.
Comparative evaluation of non-toxic and toxic varieties of Jatropha curcas for chemical
composition, digestibility, protein degradability and toxic factors. Food Chemistry 62,
207-215 (1998).
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11 Oct, 2007
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Posted by: Jonathan Gressel

Jatropha curcas: toxic disaster or fuel for the future? Bennett and Gressel both
have a point. Although even some basic agronomic characteristics of J. curcas are not yet
fully understood, the plant enjoys a booming interest, and this may hold the risk of
unsustainable practice. While our qualitative sustainability assessment, focusing on
environmental impacts and to a lesser extent on socio-economic issues, is quite favorable
as long as only degraded land is taken into J. curcas cultivation, there are several
tradeoffs between different sustainability dimensions cautioning us against jumping on
the Jatropha Express too soon. Please see Achten WMJ, Mathijs E, Verchot L, Singh VP,
Aerts R, Muys B (in press) Jatropha bio-diesel fueling sustainability? Biofuels, Bioproducts
and Biorefining, at http://www3.interscience.wiley.com/cgi-bin/jissue/114204229
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11 Oct, 2007
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Posted by: Raf Aerts

Your article was very well researched and indeed offers to India (and other
Countries with equal requirements for providing alternative sources of fuel to fossil
derived fuels) a temporary respite from 'Peak Oil.' With the developments in India
moving forward apace and the population likely to exceed that of China in less than
twenty years and the aspiration of all to have personal transport there will surely be a
need for more fuels including substitutes for refined fossil fuels Diesel and
petroleum/gasoline. I wonder then though whether the authors and researchers have
taken note of the other potential sources of Biofuels available to India. One of these is
Pongamia - the Indian Beech Nut - which was recognised by Dr. Udipi Shrinivasa from
the Indian Institute of Science, Bangalore as being of equal importance for its oil derived
fuel to be a useful source of Bio-Diesel and an equal substitute for fossil fuel derived
Diesel. From the reading of his work it would appear that this could be of more
importance to the Indian economy than Jatropha. Yet in all of these issues about the
developments of BioFuels little if ever mention is made of the fact that growing crops on
land that might also be used for growing foods has its disadvantages. With the scarcity of
such land across the world we should be careful in all that we do in case we upset the
fine balance between ecosystems in the area. Perhaps the two events in recent time that
should be referred to as a warning in this area are the destruction of the Aral Sea basin
as a result of the diversion of the source rivers to feed the Cotton Industry and the
effects of the Communal Farming initiatives in China during the 1950s and 1960s. (There
will be others in historical terms of equal note!) In respect to the options for the other
Biofuel substitute - Ethanol - for petrol/gasoline there is as much an obvious need in
India as there is elsewhere in the World (be it China, Korea, Indonesia, Nigeria, Brazil
and the rest of the South Americas or in the 'Western Nations.') The traditional route to
manufacture Ethanol again relies on the use of crops that are primary sources of food
(Sugar Cane and Beet or Corn, Wheat, Rice and Grains etc.) or they are grown on land
that should preferentially be used to grow food. This conflict between the use of Crops
(and land) for the Production of Fuel or Food will bedog us for some time unless we take
action to redress it at the earliest opportunity. One of the easiest ways to do this is to
intercept the Biomass from Waste sources and use this to manufacture the fuel Ethanol.
The process to do this Mild Acid Hydrolysis is well founded and established having been
developed in the late 19th Century and early 20th Centuries to make batch small
quantities of Ethanol for transport in the USA and Europe prior to the development of the
mass development of cheap oil in the USA and the European North Sea. With the
developments of the process in recent time by Genesyst and the use of its Internationally
patented Gravity Pressure Vessel the process is now continuous and the resulting
efficiency of conversion of Biomass to Ethanol means that it can be used on any sources
of Biomass including that found in Waste (previously considered unusable) in an emission
free environmentally acceptable and economical way at around a quarter of the cost of
the Thermal Destructive - or the Incineration - and Waste to Energy options. The sources
of the raw material available to make Ethanol now includes Biomass found in Waste from
Agriculture and Farming, Forestry, Food Production and Discards, Commerce and
Industry (including Saw Mill and Paper Manufacture, etc.), and Construction Debris and
the likes. Importantly though for Society it includes the Biomass we discard in our
Municipal Solid Waste. This source of Biomass is available from every community around
the World, and it is a constant source of material that is not affected by Climate, Seasons
or Internationally defined Commodity Prices established outside the Country of
production. In the Metropolitan City of Mumbai some figures were quoted by Surika Kamil
(for the Indira Gandhi Institute of Development Research) which gave an insight into the
issue for Greater Mumbai as follows. In 2001 the total daily production of Municipal Solid
Waste was 6260 tonnes (rounded up to the nearest 10:) The Biomass equivalent in this
same source of Waste was 3950 tonnes: Assumed Water Content of the Biomass as a
percentage 50% Potential Ethanol yield at 200 litres per dry tonne of Biomass = 144+
million litres per year. If it was possible to consider all the potential Municipal Waste
collected in the major cities in India then from the report given in the Hindu on
Wednesday March 07th 2007 where it is stated '..."The present annual solid waste
generated in Indian cities has increased from 48 million tones in 1997 to 95 million
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tonnes, which might exceed 150 million tonnes over the next seven years," says Mr.
Dhoot.' Supposing just half of this 150 million tonnes was made into the fuel Ethanol then
the comparative quantity of Ethanol derived would be nearer 4700+ million litres of
Ethanol (a not insignificant sum)! And by adding to this other waste sources of Biomass it
is possible that even India could become self sufficient in substitute Biofuels. The
comparison elsewhere around the world though is even more startling.
City/Population/MSW tonnes per day/Ethanol litres per year Buenos
Aries/12.4m/7,800/480,000,000 Beijing/15.3m/13,300/820,000,000 São Paulo
City/18.7m/15,900/985,000,000 MetroSeoul/23.9m/22,800/1450,000,000 If Brazil was
to exploit the production of Ethanol from Municipal Waste it could increase the total
country's production very significantly! By converting Biomass from its Municipal Waste to
Ethanol Metro Seoul could replace over 40% of the total petrol used in the area. So in
returning to the article in the current press We should be looking at the wider picture
when it comes to addressing the potential of Biofuel production. This should embrace the
use of Biomass as it does not impinge on the use of Crops that should primarily be used
for Food or grown on land that ought in the first instance be used for growing food. The
use of Jatropha (or indeed Pongamia) may be such a crop but even then in certain areas
it may have distinct advantages for Society.
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11 Oct, 2007
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Posted by: Peter Hurrell

Thanks for the nice, well researched reviews on Jatropha. Biodiesel from Jatropha
oil is a huge potential to reduce the spread of desert and cover arid/semi-arid land with
green shrubs. It also can enable poor, rural people in countries like India, Chain, Africa
etc to get some extra earnings. Though I have enough doubt if it can solve the problems
regarding fossil fuel in future in large scale, even in those countries. The main bottleneck
for using Jatropha is very high labour requirement collect seeds. This will be real longterm problem for its use in industrialized countries where labour cost is very high. Seed
cakes of jatropha is known to contain toxicity and not suitable for cattle feed and fertilizer.
In countries like India, jatropha has invited private investment. Their goals are not
necessarily the elevation of rural poverty and provide green cover for arid and semiarid
land. They are mostly interested to gain from Govt subsidy associated with jatropha
plantation. This also has the potentiality to force and exploit poor and mostly illiterate
farmers in villages to cultivate jatropha instead of their normal crops. This will be of great
concern in countries like India with huge population to feed. Unless proper and systemic
studies are completed to ascertain its agronomic and environmental impact, economic
feasibility (mainly for rural mass), Jatropha should not be allowed for mass cultivation.
Its use by private investors also should be properly monitored.
o
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o
11 Oct, 2007
o
Posted by: jayanta chatterjee

I am really interested to see these opinions about Jatropha curcas, not least
because I am involved in an EU AidCo funded project called RE-Impact
(www.ceg.ncl.ac.uk/reimpact) in which we are planning to develop integrated tools and
methodologies to help stakeholders and policymakers see the bigger picture when
planning energy plantations. We are looking at water resource, socioeconomic,
biodiversity and climate change (CDM and JI) impacts from global to local scales, with
case studies in India, China, Uganda and South Africa. As discussed in the article
Jatropha is already planted up in a big way in India and China with more planned, whilst
interest in Uganda is scant and there is currently a moratorium on the crop in South
Africa. All very interesting stuff, and we hope to develop the project meaningfully over
the next 3 years with input from any interested stakeholders at any level. For more
information, workshop details, or to get in touch, please do go to the website.
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o
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12 Oct, 2007
o
Posted by: Jennifer Harrison

Biodiesel, like starch-based ethanol, uses only a fraction of the plant. A winning
strategy for biofuels would be based on converting the cellulose.
o
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12 Oct, 2007
o
Posted by: Paul Braterman

The perspective on Jatropha I mentioned above, has been published online and is
available via http://dx.doi.org/10.1002/bbb.39
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20 Nov, 2007
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Posted by: Raf Aerts
Add your own comment
You can be as critical or controversial as you like, but please don't get personal or
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Published online 20 February 2008 | Nature 451, 880-883 (2008) | doi:10.1038/451880a
News Feature
Energy: Not your father's
biofuels
If biofuels are to help the fight against climate change, they have to be made
from more appropriate materials and in better ways. Jeff Tollefson asks what
innovation can do to improve the outlook.
Jeff Tollefson
D. SIMONDS
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Biotechnology has changed the way that drugs are discovered, designed and,
often, made. It has spread new capabilities across the farms of much of the world,
sometimes amid much controversy. Now some of its advocates are suggesting
that it is poised to overhaul the energy sector as well, changing both the crops
that are grown and the fuels that are made from them.
Entrepreneurs have attracted hundreds of millions of dollars for bio-energy
companies working on 'second-generation' fuels produced from crop residues,
grasses or woody materials that avoid the shortcomings of ethanol distilled from
corn starch or biodiesel produced from oil crops. Some are offering hope for
higher yields from less land, from more marginal land, and with less investment
in terms of energy and fertilizer; others are promising fuels better suited to the
needs of drivers and the existing fuel infrastructure. Even the major oil
companies are getting involved.
“The market is slated to be so big that there will be opportunities for multiple
approaches, and it will probably take many years before we settle on one
absolute best approach,” says Doug Cameron, chief science officer for Khosla
Ventures, a venture-capital firm in Menlo Park, California, that is backing a large
number of start-up bioenergy companies.
Liquid biofuels will never make up a significant portion of the global
transportation fuel supply unless biologists and engineers make the most of these
opportunities. During the past four years alone, global ethanol production has
more than doubled to nearly 50 billion litres (about 13.2 billion gallons) in 2007.
Biodiesel, although starting out much lower, nearly quintupled to 9 billion litres
(2.4 billion gallons) during the same period (see A growing concern). This rate of
growth is not sustainable — and with current production methods far from
desirable, because the agricultural techniques used often damage the
environment on a scale that far outweighs any good achieved through the
biofuels' use.
In the United States, which has ramped up production and is now home to the
world's largest biofuel industry, roughly 23% of the corn crop goes to ethanol,
which in turn provides 3% of the nation's transportation fuels, according to Alex
Farrell, an energy and resource scientist at the University of California, Berkeley.
Worldwide, biofuels make up less than 1% of transportation fuel, he says.
Current technologies could push that as high as 2–3%, “but anything much larger
than that will have to be based on significantly different technologies”.
Fuels for the future
Applying biotechnology to biofuels is not a new idea. In 1991 Lonnie Ingram, a
microbiologist at the University of Florida, Gainesville, was awarded a patent for
an engineered Escherichia coli bacterium that converts sugars into ethanol. But
only now is the technology really coming into its own — not least because today's
'metabolic engineering' and 'synthetic biology' put much more ambitious fuels
than ethanol on the table, or indeed into the pipeline.
“I've always been of the opinion that ethanol is for drinking, not driving,” says Jay
Keasling, a chemical engineering professor at the University of California,
Berkeley, who has pioneered the synthetic biology needed to get microbes to
produce various new classes of molecule. To take one example: drinking is made
easy by the fact that ethanol and water mix easily. That's good for scotch and
soda, but bad for pipelines, which give the fuel a chance to get watered down and
contaminated. In the United States, home to the largest biofuels industry in the
world, trucks or train cars carry the fuel from the agricultural heartland where
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corn is grown to the coastal areas where fuel is needed most. In Brazil, the other
biofuel giant, where sugar-cane ethanol is produced much more efficiently, the
agricultural source and the urban users are relatively close together in the
country's southeast — one of the many advantages the Brazilian industry enjoys.
This is why Amyris Biotechnologies, a start-up company in Emeryville, California,
of which Keasling was a co-founder, and a number of other small companies in
California and Massachusetts are designing microbes to make better fuels — fuels
with higher energy contents that are better suited to pipelines and other
infrastucture. University researchers are also in the race. Last month Jim Liao, a
researcher at the University of California, Los Angeles, described an E. coli in
which more than a dozen modifications to the metabolic pathways normally used
to produce amino acids caused the bacteria to produce isobutanol, an alcohol with
four carbon atoms to ethanol's two, and similar molecules. Even without
optimizing every step of the process, Liao's lab was able to achieve a yield of
86% of the theoretical maximum (S. Atsumi, T. Hanai & J. C. Liao Nature 451,
86–89; 2008).
His process has been licensed by Gevo in Pasadena, California, a start-up
company funded by Khosla Ventures, among others, which says that it hopes to
begin commercial-scale production within a few years. Gevo chief executive Pat
Gruber says that the technology could be retrofitted on an existing bioethanol
plant for as little as US$20 million: “We're not screwing around — the basic
science is done. We are going to try and get this stuff developed and into the
marketplace.”
Another form of butanol has attracted oil-giant BP and DuPont, one of the world's
largest chemical companies, which are working together on biofuels. Butanol has
a higher energy density than ethanol, offering roughly 85% of the energy content
of a standard petrol mix, compared with about 66% for ethanol; this offsets the
fact that less butanol than ethanol can be made from a given amount of biomass
(there are only so many carbon atoms to go round). Although other molecules
could pack even more energy, DuPont officials say that they settled on butanol as
a molecule that meets their needs and can be developed quickly.
DuPont has a track record in the sort of metabolic re-engineering required for
such things: the E. coli that churn out propanediol, a chemical used in various
materials and industrial processes, in its facility in Loudon, Tennessee, have had
30 changes made to their metabolic pathways. It took about 11 years for that
project to get from the proof of concept to production, but officials say biobutanol
could be sorted out much faster. “In the old days, it would take four to six
months to clone a new gene,” says John Pierce, DuPont's vice-president for
applied biosciences. “Now it takes two weeks and you usually do it by mail.”
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View an enlarged version of the
graph.
Butanol's advocates say that their fuel could be run through a refinery to produce
longer chain molecules as desired. Amyris and LS9 of Cambridge, Massachusetts,
are looking to skip this step and move straight to molecules more like those that
engines already burn. Both companies specialize in synthetic biology — which
aims to create new biological entities in a much more thoroughly designed way
than traditional genetic engineering — and both have received backing from
Khosla Ventures, among others.
LS9 was co-founded by George Church, a geneticist at Harvard Medical School in
Boston, Massachusetts, and Chris Somerville, a plant biologist at Stanford
University in California, who previously headed the Carnegie Institution's
department of Plant Biology. Somerville is currently heading the new Energy
Biosciences Institute (EBI), a partnership between the University of California,
Berkeley, Lawrence Berkeley National Laboratory and the University of Illinois at
Urbana-Champaign. The EBI was kick-started in 2006 with a $500 million pledge
from BP.
Different pathways
LS9 wants to transform the fatty acids naturally produced by E. coli into specific
hydrocarbon fuels; it has announced plans for a pilot plant and says that
commercial production could begin within two to three years. Amyris decided to
take yeast, which is known for its ability to make ethanol, and train it to produce
longer-chain molecules such as gasoline, diesel and jet fuel.
The company has engineered roughly 1,000 strains of yeast so far and expects to
build as many as 2,000 more in the months ahead. When a strain looks promising,
the scale-up begins, as molecular biologists hand their product to chemical
engineers and fermentation engineers. In addition to producing exactly what is
needed, Jack Newman, Amyris's senior vice-president for research, says that the
technology could prove to be extremely versatile. “You could have your plant
making diesel fuel one day and almost literally turn around and make jet fuel the
next.”
Wood pulp and fiction
All these companies are looking at traditional raw materials for their wonderbugs
— sugars. And this means that although they may make more attractive and
easily distributed fuels, they will not of themselves change the industry's
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productivity. To do that requires cheaper and more sustainable feedstocks than
sugars and starches from cane and corn.
“I'm of the opinion that the crucial thing that needs to be done is not actually to
make better fuels out of sugars but to make sugars more efficiently from
cellulose,” says Lee Lynd, a biology and engineering professor at Dartmouth
College in Hanover, New Hampshire. “The thing that limits corn ethanol, frankly,
is not ethanol — it's corn. Those other molecules will become important in the
broader scheme of things if and when we solve the problems with cellulosic
biomass.”
Turning cellulose — the tough polymer from which the cell walls of plants are
made — into biofuel is currently a major focus in the industry. It widens the
possible range of feedstocks greatly, making it possible to use crops for biofuels
that are not also food for humans. Legislators are keen to push the industry in
that direction. The ethanol mandate enacted by the US Congress in 2007 requires
that, of an annual ethanol production of 136 billion litres (36 billion gallons)
required by 2022 — more than five times current US production — 44% must
come from cellulosic foodstocks, with corn's contribution remaining static from
the mid 2010s. Things might be able to go even further. A report by McKinsey &
Company, a consultancy firm based in New York, suggests that, at oil prices
above $70 per barrel, cellulosic feedstocks could supply half of the global
transportation fuels by 2020 (although that figure explicitly ignores many realworld constraints).
The fly in this ointment is that the world cannot yet boast a single commercialscale cellulosic-ethanol facility. Breaking cellulose down into sugars is not easy
work, and can use up a lot of energy; what's more, not all the sugars produced
are easily fermented. Despite the recent spike in oil prices on the international
market, lenders and investors have hesitated to pump money into commercialscale ventures, fearing technical risks and a potential drop in the price of oil. To
help push the technology over the first economic hurdle, the US Department of
Energy (DOE) is pumping $385 million into six demonstration projects. Work
begun on the first of them, run by Colorado-based Range Fuels, in Georgia last
autumn.
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R. KALTSCHMIDT/LBNLE
Cellulose can be broken down with heat and catalysts. It can also be broken down
with biology. This is where biotechnologies can come in. Dartmouth's Lynd is the
co-founder and chief scientific officer for Mascoma Corporation in Cambridge,
Massachusetts, which is pursuing work on a bacterium that can produce the
enzymes to break down cellulose on demand as part of the process. Verenium
Corporation, also in Cambridge, the first publicly held cellulosic-ethanol enterprise,
is developing both new enzymes and organisms to break down the structural
tissue. Other companies and researchers are looking to the microbes that break
down cellulose in the guts of cows and termites, or to fungi — that is to say, the
natural world's most accomplished consumers of the cellulose found in grasses
and wood.
Finding a feedstock
If cellulosic technologies can be made to work, there's still the question of where
the cellulose comes from. For the past ten thousand years, most human meddling
with the proclivities of plants has been designed to make them better to eat —
more sugar in the cane, more starch in the corn, more protein. Energy crops,
though, require a different approach. No need for fruit or seed — just for fast
growing cellulose, ideally in a form that requires little or nothing by way of extra
inputs such as fertilizer. Cellulose that is particularly easy to break down gets
bonus points.
Switchgrass, a hearty, fast-growing grass native to America's prairies, is one
much-touted possibility, but even a brief survey indicates that there could be
better options. Steve Long, a professor at the University of Illinois at UrbanaChampaign, has spent years studying Miscanthus giganteus, a relative of sugar
cane that is native to East Asia. He has studied the grass in Denmark, England
and now Illinois, and says that the average yield is double that of switchgrass and
50% higher than corn — without any fertilizers.
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According to Long, meeting the ethanol goals laid out in 2006 by President Bush
(which were a touch lower than the mandates actually passed by congress) with
corn ethanol would require 25% of the nation's cropland. That figure drops to
15% if cellulosic technology allows you to make use of the corn 'stover' — the bits
left over after harvest. It drops to 8% if you use M. giganteus — and such
grasses could be grown on marginal land that is not being used for food
production today.
And, according to Long, neither stover nor M. giganteus are the last words. “A lot
of effort is being invested in modifying corn stover to make it easier for digestion,
but I think we need to think much more broadly,” he says. “It seems very
unlikely that we've come across the very best option.”
Whichever crops look most promising, engineers will be eager to tinker with them.
Keasling says that a decade of intensive biotechnology could now do for an
energy crop as much as centuries of selective breeding have done for many food
crops. New models of cultivation may help too — for example the replacement of
monocultures, which are useful if you want a particular form of food, with
polycultures that simply maximize biomass. David Tilman and his colleagues, at
the University of Minnesota in St Paul, reported last year that plots with a diverse
mixture of prairie grasses yielded on average 238% more energy than plots with
a single crop (D. Tilman, J. Hill & C. Lehman Science 314, 1598–1600; 2006). All
these approaches might be tailored to marginal lands where the soil wouldn't
support food crops.
Or you could just do away with soil altogether: that's the appeal of algae.
GreenFuel Technologies, based in Cambridge, Massachusetts, is developing algal
bioreactors that tap into carbon-dioxide streams from coal plants to produce rich
algal crops that can be harvested and turned into biofuels. A more ambitious
approach would be to have the algae act as both feedstock and processor,
secreting ready-made fuels. Tasios Melis at the University of California, Berkeley,
is looking at getting algae to secrete hydrocarbons in a form that can be
continuously collected.
As it is today: this VeraSun
Energy plant near Aurora, South Dakota, produces 450 million litres of
corn ethanol a year.E. LANDWEHR/AP
Botryococcus braunii, the green alga that Melis is working with, naturally secretes
a 30-carbon terpenoid that can be processed into fuel, perhaps in order to reduce
the effects of ultraviolet light. Melis says that he has devised a method for
collecting the product — a sticky film to which the algae adhere — and is now
working to increase production. More ambitiously, various groups, including Melis,
are looking at having algae produce hydrogen.
Another approach, taken by Coskata in Warrenville, Illinois, (yet another Khosla
Ventures start-up) and its partner General Motors, is to avoid putting effort into
specialist feedstocks and instead develop a process that works universally.
Coskata's process converts carbon-based feedstocks, which could be crops,
agricultural waste or municipal waste, into carbon monoxide and hydrogen. This
is the first step of processes by which coal or natural gas are turned into liquid
fuels, a procedure that is normally taken as an alternative to biological means for
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producing fuels. Coskata says it has a way of combining the two approaches, with
microbes that turn the 'synthesis gas' straight into ethanol. The company is
currently developing a pilot project that it says will be able to produce ethanol for
less than 26 cents per litre ($1 per gallon).
Scaling up
One thing all these innovations share is that they have yet to be attempted on a
large scale. Biotech may work well for drug companies that sell small volumes at
premium prices, but the economics of biofuels are more in line with the oil and
gas industries, which sell in bulk for low prices and are dominated by the cost of
raw materials and manufacturing.
ADVERTISEMENT
One of the problems is that microorganisms evolved to take care of themselves,
not people. Re-engineering their metabolisms in such a way that they excrete
fuels — which by definition are energy-rich compounds — means convincing them
to forgo energy that they might otherwise use to their own ends. Moreover, in
many cases the fuels can be toxic to the organisms themselves. All this provides
ways for the engineering to come unstuck.
“If [the microbes] are unhappy with what they are doing, they are going to
evolve away from what you want them to do,” says genome entrepreneur Craig
Venter, whose company Synthetic Genomics in La Jolla, California, has an interest
in biofuel production. “A key part of the future is going to be designing a system
where they are not grossly unhappy with what they are doing.” Many researchers
see hope in producing longer-chain biofuels precisely because it decreases the
stress on the microbes doing the work. Ethanol is poisonous to its producers
(which is why fermentation can't on its own produce hard liquor — the yeast dies).
Longer-chain molecules will separate out from the medium in which their
producers grow; this avoids the costly step of distillation.
Even if the microbial producers can be kept happy, there's a lot more work to do
in producing systems that will work on an industrial scale in commercial refineries.
“Among scientists it's considered very doable,” says Michael Himmel, who heads a
team of researchers working on cellulosic ethanol at the DOE's National
Renewable Energy Laboratory in Golden, Colorado. “It's difficult work and it's
going to take some funding. But it's not cold fusion.” But what's doable in
principle to a scientist is not always practical to an engineer.
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Big oil companies, which would have the know-how for such engineering, are
keeping an eye on the field. As well as BP's work with DuPont, Shell is partnering
with Iogen in Ottawa, Canada, which ran one of the DOE's cellulosic pilot plants,
and with an algal biofuel producer in Hawaii. But all this is small compared to the
investments such companies make in their oil-based business.
D. SIMONDS
Biofuels will never take over the whole liquid-fuel market, let alone amount to a
large proportion of total energy use. But they, and other technologies, have a
part to play. A decade and a half after receiving his patent on an ethanolproducing bacterium, Ingram is still a biofuel enthusiast. But he's also a realist. In
the same law that expanded the ethanol mandate, Congress also increased the
fuel-efficiency requirements for vehicles by 40%, pushing the average efficiency
required by 2020 up to 6.7 litres per hundred kilometres (35 miles per gallon)
from the present average of 9.4 litres per hundred kilometres (25 miles per
gallon). The technologies to do that are already available — Japan had an
average fuel efficiency of 5.1 litres per hundred kilometres in 2002. And as
Ingram points out, “If we increase gas mileage by 1 mile per gallon, that is about
equal to all the ethanol we are making right now from corn.”
Jeff Tollefson covers climate, energy and the environment for Nature. See
Editorial, page 865.
Comments
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
o
I was surprised by the lack of mention of Searchinger and Tilman's recent Science
papers on the enormous breakeven times of biofuels. We unfortunately don't have
decades to solve our greenhouse gas emissions problem. Biofuels will also have a tough
time supplying anything but a small fraction of our energy because plants are so
inefficient. Fundamentals of Renewable Energy Processes gives the solar energy to
ethanol conversion efficiency of sugarcane (one of the best) as 0.13%. If you compare
this to the 30% of a Stirling dish, you've got a factor of 231. Worse, ethanol, butanol, etc.
are converted into mechanical energy far less efficiently (much less than half) than the
output from a Stirling dish (heat engines are subject to the Carnot limit after all). All of
this translates into enormous differences in land area to create the same amount of work.
In my opinion, the land area requires should be a primary criteria for evaluating
renewable fuels.
Report this comment
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o
20 Feb, 2008
o
Posted by: Earl Killian

There is talk in this article of growing sources of cellulose on “marginal land�
or with no fertilizer inputs. However, unless you recycle the wastes from the energy
production process back to the soil the cellulose was grown in it will eventually become
depleted for e.g. phosphate – and growth of plants that even tolerate low phosphate
levels will become restricted. This is not a small problem since a Hubbert linearization
analysis of mineral phosphate extraction predicts that this resource is 75% depleted!
( See www.energybulletin.net/33164.html and www.energybulletin.net/40300.html )
Phosphate extraction from lower quality sources would require greater energy inputs.
This means that, if any phosphate for fertilizer is available in 10 years time, it will be
exceedingly expensive. The looming phosphate shortage has enormous implications for
biofuels and, more importantly for the continuation of western industrial agriculture.
o
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20 Feb, 2008
o
Posted by: Michael Lardelli

The article failed to discuss that there is one cellulosic feedstock that is readily
available and at present has negative environmental value, the 2 billion tons of straw
available world wide. Straw eventually becomes carbon dioxide without providing value,
and at the same time temporarily binds nutrients, causing farmers to overfertilize. Straw
also harbors pathogens requiring fungicide use which is why it used to be burnt in the
field. The use of this byproduct would not necessitate putting new land in cultivation. The
major problem with all the crops being used as cellulosic feedstocks is that they have not
been domesticated for use as biofuel feedstocks. The main problem is lignin, which
prevents metabolism of cellulosics by the wonderful microorganisms being developed (as
described by the author). All the cellulosics described must be pretreated with heat and
acid before the microbes can be used. Reducing and modifying lignin by genetic
engineering of the cellulosic crops, whether switchgrass, Miscanthus, or straw from crops,
can substantially reduce the amount of pre-treatment, as has already been demonstrated
in the pulp and paper industry in transgenically modified trees. The potential uses of
biotechnology for developing biofuel feedstocks is described in a recent review:
“Transgenics are imperative for biofuel crops. Plant Science 174: 246-263 (2008).�
o
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o
23 Feb, 2008
o
Posted by: Jonathan Gressel

What do people think of this technology? They claim to have discovered a way to
produce ethanol from more woody plants without requiring additionl energy.
http://www.missionbiofuels.com/uploads/Announcement-Ligno-cellulosic%20Ethanol31108(final).pdf
o
Report this comment
o
04 Nov, 2008
o
Posted by: Kim Sweeny

Befouls are produced by anaerobic digestion of feed stocks that contains very small
amounts of sulfur compounds. For example garlic and onions are very rich in sulfur. This
produces very small amounts of highly toxic , flammable hydrogen sulfide , the worst
green house gas that humanity does not need. Even sulfate ions in water used in the
digestion process can produce this green house gas. It is millions time worst green house
gas than CO2 or Methane. Hydrogen sulfide might be the culprit for the disappearance of
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the dinosaurs. A very simple example is when you eat garlic and onions you produce
hydrogen sulfide that smells like rotten egg. This can explain the word holy cow. They
had a camp fire during Christmas times after the loose cow consumed large amounts of
onions. When the cow farted next to the camp fire , the blaze from the anus of the cow
was very strong with yellow bluish color ( color of hydrogen gas with sulfur impurities).
They called her holy cow. Mike Reda Consultant Saskatoon SK Canada
Published online 26 March 2008 | Nature 452, 400-402 (2008) | doi:10.1038/452400a
News Feature
Chemistry: The photon trap
Chemists have long wanted to recreate photosynthesis in the lab — and to
improve on its efficiency at converting sunlight into fuel. Katharine Sanderson
reports on their latest efforts.
Katharine Sanderson
Fuel from the Sun: these silicon
nanorods are designed to capture energy from sunlight to split water.B.
KAYES, M. FILLER
Solar cells can take sunlight and produce a current, giving instant power. But as
soon as the Sun goes down, the lights go dim. If you could turn sunlight into fuel
— to use for transportation or simply to store for later — you'd be on to a good
thing.
Nature can already do this thanks to photosynthesis. Green plants take water,
sunlight and carbon dioxide to make sugars and starches. This provides all the
fuel they need, and most of the fuel we need too, in the form of food or oil.
The problem is that plants aren't very efficient at fuel making — only about 3% of
the Sun's energy ends up as a useable fuel. And the fuel that works for plants
doesn't necessarily work for us — the sugars and starches have to be further
processed if our needs are more sophisticated than simply eating or burning.
But where plants excel is in getting electrons out of water to produce a fuel. A
photovoltaic system, or solar cell, is simply a means of shifting electrons from
one place to another. To make a fuel, the electrons are siphoned off, and stored
in chemical bonds.
Plants get their electron supply from water. Chemists worldwide are trying to
design synthetic systems that do the same. And the design they have to beat, or
at least mimic, not only works at room temperature, it does so without the need
for expensive metal catalysts. Making something cheap and similar to the
machinery used by plants, the photosystem-II protein complex (PSII), remains a
fundamental challenge.
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Some US chemists taking on the challenge are part of a collaborative effort called
Powering the Planet, backed by the National Science Foundation. Three basic
chemistry problems, each tackled by a different research team, form the crux of
the project. One is to design an affordable material to collect energy from the Sun
and convert it into current (led by Nate Lewis at the California Institute of
Technology, or Caltech). Another is to perfect a catalyst at one end of the
material to split water and produce oxygen (led by Dan Nocera at the
Massachusetts Institute of Technology). And, the third is to design another
catalyst at the other end to produce hydrogen, to be used as a fuel (led by Harry
Gray, also at Caltech).
“We've made dramatic advances,” says Gray, who can be seen as the father of
the project, having supervised both Nocera and Lewis as students in the 1980s.
“We're not close to assembling the full device yet.”
To start the fuel-making process, sunlight hits a photo-active material. In plants
this is chlorophyll, but in the lab it can be a silicon semiconductor, which has its
electrons whacked out of position by the incoming photons. The dislodged
electrons start to flow in one direction, creating a current. Left behind are positive
charges, known as holes, and they drift in the opposite direction. This is a basic
solar cell, which requires silicon of high purity, otherwise material defects cause
the electrons and holes to recombine, reducing its performance.
Plant power
In the Powering the Planet design1, catalysts at either end of the semiconductor
are used to drag the electrons and holes out of the system, preventing them from
recombining with each other (see graphic). And water is added to provide the raw
material for making the fuel.
One catalyst uses the holes in the semiconductor to drag further electrons from
water. This process splits water, releasing oxygen and positively charged
hydrogen ions (protons). These protons flow to the other catalyst, which
combines them with the electrons in the semiconductor ultimately to make
hydrogen molecules.
As well as providing hydrogen fuel for combustion, both the hydrogen and oxygen
gases can be fed into a fuel cell — a means of reacting hydrogen with oxygen to
produce water and electricity for powering an electric vehicle.
Harry Gray uses sunlight to make
hydrogen fuel.B. LAI
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There are other ways to split water artificially. In 1975, Nobel prizewinning
physicist Jack Kilby invented an electrolysis system that used power from a solar
cell to drive electric current through a water-based solution (an electrolyte). This
process produced protons and hydroxide ions, which reacted at the electrodes to
make hydrogen and oxygen.
Aside from Kilby's simple system, more complex electrolysis cells have been built
that use a photoactive semiconductor coated on one side with a platinum catalyst
as one of the electrodes. When immersed in water, the semiconductor can both
harvest light and generate the electrons and holes needed to split water into
protons and oxygen. Hydrogen is released directly from the surface of the
semiconductor, and oxygen is produced at a second platinum electrode.
This cell was built in 1998 by John Turner from the National Renewable Energy
Laboratory in Golden, Colorado. His device converted water to hydrogen with
12.4% efficiency, four times as good as photosynthesis. But Turner had to use
expensive materials such as platinum, the system had a lifetime of just 20 hours,
and the hydrogen produced cost US$13 per kilogram2. “We can do better,” says
Turner.
The problem with all electrolysis systems is that the electrode materials degrade
rapidly in solution, and need to be replaced, increasing costs and decreasing
efficiency. The main difference between Turner's cell and future technologies will
be the materials used, with the precious-metal catalyst and expensive singlecrystal silicon superseded by cheaper materials. “If we're going to solve this
problem we can't use materials that are toxic or expensive,” says Gray. “This
rules out most standard catalysts.”
Nate Lewis is leading Powering the Planet's light-harvesting effort. His team is
refining a silicon material that he describes as “cheap and scaleable”. Instead of
expensive single-crystal silicon, Lewis's photoelectric material is a carpet of
nanoscale silicon rods, all pointing upwards. He's done this work with Harry
Atwater, director of the Caltech Center for Sustainable Energy Research.
The rods are each single crystals, but the method used to grow them is much
simpler than the precision wafer-processing technology needed for conventional
solar cells. Atwater claims that this makes the rod silicon only as expensive as the
silicon feedstock, at between $40 and $70 per kilogram.
The nanorods are also amazingly defect-free. “Once a nanowire begins to grow a
little taller than it is wide, it expels defects,” says Atwater. This means that the
only place where the holes and electrons could recombine is at the tip of each
tiny rod.
In the device imagined by the Powering the Planet team, Lewis and Atwater's
silicon-rod carpet will be held inside a plastic membrane. The catalysts are coated
on opposite sides of the membrane to prevent the oxygen and hydrogen reuniting,
potentially explosively.
Catalysing success
Harry Gray is making good progress at the hydrogen-producing end of the system.
His catalyst is a cobalt molecule. “It works really well, with quite reasonable
efficiency,” he says. This rather depends on your expectations. In catalysis,
turnover rates are used to measure how many substrate molecules are converted
to a product each second. Hydrogenase enzymes, which power the same reaction
in plants, have turnovers of about 6,000 per second2, but Gray's catalyst is still a
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factor of a thousand less efficient than the hydrogenase enzyme, he says. “We
have a proof of principle, but we have a long way to go,” says Gray.
Dan Nocera, at the Massachusetts Institute of Technology, Cambridge, is
developing the oxygen-producing catalyst, which is proving to be the hardest part
of the challenge. Nocera's team began by looking at expensive metals that are
related to cheaper metals: a trick often used by chemists. Choose a target metal
that could be potentially used, then look at its position in the periodic table and
move down a row to a heavier, more expensive metal, where processes happen
more slowly, and are more easily studied. Nocera has been using ruthenium,
directly below iron. He hopes to transfer what he has learned to iron, copper or
nickel, and is confident that this leap will happen soon, making a working system
possible within five years, he says.
James Durrant, a chemist at Imperial College London, is also investigating watersplitting materials. He is well aware of the chemistry problems faced by Nocera in
his quest for a cheaper catalyst. “Oxidizing water is vicious chemistry,” he says.
The catalytic reactions involve molecules undergoing multi-electron processes,
which are poorly understood. “As bad as it is to transfer one electron, the
molecule is even more reluctant to give up the second electron,” explains Atwater.
This is because adding solar energy to water, and tying it up in molecules with
higher energy bonds (oxygen and hydrogen) is what's known as a
thermodynamically uphill process. And most of that uphill struggle happens at the
oxygen-producing site. Making a single molecule of oxygen involves splitting two
water molecules, and the whole process involves four electrons and four protons.
“That's a lot of electrons and protons,” says Nocera. For this reason, Nocera says
he doesn't want to simply copy photosynthesis. “It took two billion years of
evolution,” he says. “I don't think I can do it in 20.”
Chemists want to replicate
photosystem II (modelled above), used by plants to convert light into
fuel.J. NIELD
Other chemists are still trying to beat nature at its own game. A dozen European
research partners, coordinated by Stenbjörn Styring from Uppsala University,
Sweden, form the Solar-H network, funded by the European Union. They are
looking closely at natural photosynthesis for inspiration.
To harvest energy from sunlight, the Solar-H team uses a ruthenium-centred
molecule that helpfully absorbs light at a similar wavelength to chlorophyll. For
the hardest part of the problem — the oxygen catalyst — the Solar-H team turns
to the heart of PSII, which contains a molecule with four manganese atoms
known as the oxygen-evolving complex.
Styring has been working on this problem for 15 years, and he has shown that it
isn't necessary to fully replicate the oxygen-evolving complex. Instead, he thinks
that just two manganese atoms are sufficient. Styring says he has recently had a
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breakthrough: a molecule that can split water into oxygen and protons, although
the system is powered electrochemically, not by light.
Even after this prolonged effort, Styring expects criticism when he publishes the
work, partly because the oxygen-evolving molecule isn't fully catalytic — the
molecule is changed by the reaction and so probably cannot be reused. “People
will be very sceptical, and so are we,” he says. “This is a very difficult field.”
He will have a hard time convincing researchers such as Durrant. “The only
molecular system known to perform thermodynamically efficient water oxidation
is PSII,” says Durrant. “We're a long way from having a molecular system that
works as well,” he says.
Other chemists say that simply mimicking photosynthesis is too short sighted.
“Photosynthesis is basically a failure for energy conversion,” says Tom Mallouk at
Pennsylvania State University. To beat the world's energy problems, scientists
have to be more ambitious than the 3% efficiency achieved by plants. “If that's
all we want, the thing to do is grow corn,” says Mallouk. He thinks the goal should
be at least 10%, preferably 20% power conversion efficiency, using materials
that do not cost much more per unit area than house paint, he says.
The Powering the Planet team is optimistic it can beat photosynthesis, even if it
doesn't beat Turner's efficiency record. And they are determined to beat Turner
on cost. “In the end, we want to be at 5–10% solar-to-fuels efficiency,” says
Lewis. “We know the materials that work. It's just a question of making it work
faster, better, cheaper.”
Another materials approach to water splitting is being taken by Kazunari Domen
at the University of Tokyo. In future, says Domen, if human beings use solar
energy on a huge scale, we need to use technology that captures solar energy
over much larger areas. To achieve this, he uses a photocatalyst particle that
generates hydrogen and oxygen simultaneously on its own surface. The material
is a solid solution, a mixture of metal oxides impregnated with nanoparticles of
another mixed oxide. Domen is still developing these materials, which as yet
don't work for all wavelengths of light.
Domen admits there is still lots of basic research to be done. Indeed, all of the
groups defend their work as basic chemistry first — and applied research second.
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“We're doing fundamental chemistry, unashamedly,” says Lewis. “There's lots of
basic stuff to do to solve this.”
To get a fully practical system may take years, although Atwater thinks that the
silicon-rod carpets are already ripe for commercialization as light-capturing solar
panels. A few small companies are investigating water-splitting, including
Nanoptek, a start-up firm in Maynard, Massachusetts, which is building on the
original Kilby approach by developing photoelectrodes that will harvest photons
over a wider energy range.
Fueling the future
G24 Innovations (G24i) in Cardiff, Wales, is developing small-scale electricity
generating systems based on organic dyes — again mimicking nature's use of
chlorophyll in photosynthesis — for personal electronics, mobile phones and
laptops, with the goal of bringing these mass communication devices to remote
parts of the world. The company's first products — solar-powered chargers —
rolled off the production line in February.
The approach is based on technology pioneered by Michael Grätzel at the Swiss
Federal Institute of Technology in Lausanne. In his photoelectrochemical cells, the
amount of silicon needed is greatly reduced, because the expensive
semiconductor is used purely to ferry electrons and holes around, and sunlight is
captured by an organic dye. But G24i's products only generate electricity, rather
than convert sunlight to fuel.
ADVERTISEMENT
There are different opinions in the field about when a commercial fuel-generating
device will become reality. Where Atwater sees immediate commercial
opportunities for his part of the project, Durrant can't see there being anything
practical working for at least ten years. Gray thinks the problem requires at least
another three or four years' work, and can see good motivation for pushing ahead.
“This is a big deal in terms of competitiveness and innovation,” says Gray. “When
solar energy comes in big time this is a trillion-dollar business.”
Turner wants to see a longer-term approach to pay for this kind of research. For
the past 30 years, he says, funding has been “spotty and not focused”. This is a
mistake, he thinks, if the future energy needs of the world are to be met.
“Sunlight is truly our largest energy resource by far — it outshines everything
else.”
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Published online 26 November 2008 | Nature 456, 436-440 (2008) |
doi:10.1038/456436a
News Feature
Car industry: Charging up the
future
A new generation of lithium-ion batteries, coupled with rising oil prices and the
need to address climate change, has sparked a global race to electrify
transportation. Jeff Tollefson investigates.
Jeff Tollefson
Download a pdf of this
story.
"We have had a massive shift in one of the biggest industries in the world," says
Stephan Dolezalek, who leads the CleanTech group at the venture-capital firm
VantagePoint Venture Partners in San Bruno, California. Dolezalek has been
watching the global automobile sector embrace the idea of plug-in electric cars:
"In three years we've gone from thinking 'it can't be done' to not only 'it can be
done' but 'we are all going to do it.'"
The shift is partly a story of technological innovation, which has produced
rechargeable batteries that pack enough power to propel some of the basic
passenger vehicles currently being designed further than 200 kilometres. Billions
of dollars have poured into start-up companies that promise new batteries, and
billions more have poured into fledgling electric-car manufacturers eager to take
on the global automotive giants — every one of which is also developing electric
vehicles.
The shift is also a story of oil supplies, national security and global warming.
Record-high oil prices have pushed consumers towards fuel-efficient vehicles and
prompted many governments to consider electric transport as a way to escape
their dependence on imported petroleum and to address climate change. Money
currently spent abroad could instead be spent on domestic power generation from
wind, solar and other low-carbon energy sources.
“Don't worry about charging electric cars from some perfect grid of the
future – just get the cars out there.”
Mark Duvall
And the shift is a story of a shared vision: developing the technology that would
entice all drivers to plug in rather than fill up. Millions of battery-powered cars
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plugged into an increasingly green electric grid would not only save drivers
money and reduce greenhouse-gas emissions, it would also provide the grid with
a distributed, high-capacity storage system for electricity. Such a system would
help to accommodate the variable and unpredictable nature of renewable
electricity sources. And further out, it could allow power companies to store
energy generated during times of low demand, then draw it back again to meet
peak demand. The end result could be more a stable and efficient grid that might
even lower home electricity bills.
Getting there won't be easy. All these hopes hinge on battery technology that is
only just emerging from the lab. A suite of technical challenges remains to be
overcome, and it is not yet clear how much further the technology can be pushed.
At the same time, the manufacturers who are arguably best able to bring about
these changes — the global automotive giants — have been hammered by an
energy crisis followed by an epic financial meltdown.
None of them has abandoned the effort yet, in large part because they all believe
that, despite the current lull, oil prices have nowhere to go but up. Moreover,
batteries have leapt ahead of expensive hydrogen fuel cells as the technology of
choice for getting beyond oil, at least for now. But the field is wide open in terms
of bringing them to market. Dolezalek believes that major car companies might
well perish in the face of versatile young upstarts, and he isn't alone. The
automobile industry secured a place in this autumn's first round of economic
bailouts from the US government with US$25 billion in loan guarantees for
retooling its plants, and it is already seeking more. That has people such as
Andrew Grove, former chairman of Intel, who has become a leading proponent of
electric transportation, talking about the 'valley of death' that often accompanies
a massive technological transformation. Grove says that car manufacturers have
already begun their march through the valley, knowing that many won't make it
through to the other side.
"The only time people make these moves [through the valley] is when things are
rough, but they can't afford to make them when times are rough," Grove says.
And that means that governments might have to step in. "I just hope that it's
going to be done in such a way that the government says, 'I'll give you some
water and food to get through the valley of death, but don't turn back.'"
Building a better battery
Pioneers have turned back before, most notably General Motors. In 1996, the US
company released the EV-1, the first all-electric car from a major manufacturer.
The vehicle was expensive, rolled out in response to a California mandate, which
was later rescinded, for 2% of all cars sold in the state to have zero-emissions by
1998. But its fate was ultimately sealed by one thing: its battery.
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Click for larger image.
Building batteries has been an exercise in chemical compromise for more than
two centuries. The idea is simple: chemical bonds can be used to trap ions in one
electrode. When a battery is hooked up to a circuit, the ions flow through a
separator to a second electrode; as the ions flow, they release electrons,
generating an electric current. In rechargeable batteries, the chemical reaction
can be reversed to store energy (see graphic, right). But the reality is complex:
although scientists have produced numerous potential battery chemistries (see
Nature 451, 652–657; 2008), none of them performs well on all the crucial
factors of cost, safety, durability, power and sheer capacity.
The first-generation EV-1 deployed a lead-acid battery, still the technology of
choice for conventional vehicles. Lead-acid batteries are safe, cheap, long-lived
and reliable, but they are also big and heavy. They could push the car for about
150 kilometres per charge. A second-generation vehicle released in 1999 featured
a nickel metal hydride battery, and travelled 50% farther on a charge, but
General Motors cancelled them after the first year, saying that it could not sell
enough to make them profitable.
The plug-in Prius uses electricity
mostly to improve the efficiency of its petrol-powered motor.J.
SULLIVAN/GETTY IMAGES
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It was a decision that General Motors would come to regret. As it turned back to
large and profitable vehicles such as the Hummer, its up-and-coming Japanese
rival Toyota was digging into the new technology, using the same battery that
General Motors had abandoned to produce hybrid cars that combined a standard
combustion engine with an electric motor. Toyota has gone on to set the standard
for hybrids: its third-generation Prius has been immensely popular, proving that
consumers will adopt advanced battery technology in automobiles if it is done
well. The Prius fortified Toyota's reputation, and helped it to surpass General
Motors last year to become the largest automobile manufacturer in the world.
But nickel metal hydride batteries can be developed only so far. These batteries
pack more power than standard lead-acid ones but can be permanently damaged
if allowed to discharge too far. To maintain an adequate safety margin, Toyota
limited the Prius to using about 20% of its battery charge during normal
operation. But although not using 80% of the capacity is acceptable if the battery
is simply supplementing a petrol engine, it is a luxury that fully electric cars can't
afford. Electric cars need all the charge they can get, and that means new
chemistries.
Lithium-ion batteries, which are compact and have a high capacity, are a natural
place to start. Sony paved the way with the lithium cobalt oxide battery, which
made its mass-market debut in a 1991 version of the firm's HandyCam video
camera, and is now widely used in consumer electronics. Lithium is a light metal,
and the lithium cobalt oxide lattice structure allows plenty of space for the give
and take of ions. But scaling this chemistry up for vehicles is problematic. Cobalt
is expensive and toxic, and the batteries have been known to show 'thermal
runaway', battery lingo for fires or explosions. "It has affected a tiny, tiny fraction
of all of the batteries sold, but nonetheless, it's pretty freaky to think about a big
fire in one of the vehicles," says Jeff Dahn, who works on advanced battery
technology at Dalhousie University in Halifax, Canada. "Safety really needs to be
the focus for the research community."
Many of the lithium batteries under development for vehicles replace cobalt
oxides with manganese oxides and iron phosphates. Both are safer, but they do
have their own problems, not least of which is a lower storage capacity for their
size. Another challenge has been dealing with the physical expansion and
contraction of the electrode material as the lithium ions flow back and forth
during charge and discharge, which can lead to fractures. Researchers at multiple
institutions have addressed the issue by adding carbon and other substances to
the electrode material.
The Chevrolet Volt runs on
electricity, with a petrol motor to help it go further.T. KIENZLE/AP
They are also probing other chemistries — often at the nanoscale — based on
silicon, fluorides and oxygen, which have a greater capacity. Others are looking at
equipping the battery pack with capacitors, which can rapidly store and discharge
electricity.
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Even in their current state, however, lithium-ion batteries are performing well
enough to keep car manufacturers interested. Last year, General Motors
inaugurated the race for mass-market electric vehicles when it announced plans
to market its plug-in hybrid, the Chevrolet Volt.
A break with the past
The Volt, now scheduled for a 2010 roll-out, is a radical shift in design. Hybrids
such as the Prius are powered by petrol, and use a battery simply to improve fuel
efficiency. The Volt hybrid will be the reverse: an electric car that uses petrol to
extend its range. Only when the charge dies will a small petrol motor kick in to
charge the battery, which then continues to power the vehicle. The goal is for Volt
owners to plug in at night and then drive more than 60 kilometres a day on a
single charge — before burning a single drop of petrol. Given that as many as
80% of US drivers commute less than that on an average day, such vehicles
could eliminate a sizeable chunk of the nation's oil consumption.
The Volt initiative could open the door to a new kind of transportation system — if
the company can pull it off, both on time and at a cost that will tempt consumers.
Many observers have their doubts. "They are fundamentally redefining what a car
is, but can they do it? I don't know," says Don Hillebrand, who heads the Center
for Transportation Research at Argonne National Laboratory in Illinois. "When the
first generation of anything comes out, to a certain extent car manufacturers are
rolling the dice, and this is the biggest roll of the dice anybody has ever made."
Some say it is a long shot. With sales plummeting in the midst of a deepening
recession, the company is facing possible bankruptcy, and has joined with the
other major US car manufacturers in seeking an additional bailout from the
government. But through it all, General Motors has continued to sink everything it
can spare into the Volt, viewing it as a key technology that would allow the
company to leapfrog its competitors.
“Safety really needs to be the focus for the research community.”
Jeff Dahn
Toyota is taking a more measured approach with its plug-in hybrid, which is
expected to roll out with a lithium-ion battery in 2009. John Hanson, a
spokesman based at Toyota's US headquarters in Torrance, California, talks about
managing customer expectations: the company is promising only that the vehicle
will go "at least" 16 kilometres on an electric charge. After that, it will blend
petrol and electric power in much the same way as the current Prius.
That would leave General Motors in pole position, at least in terms of the electric
range it is promising. But will the Volt succeed? The answer to that question
depends on consumers. What will they want several years from now? And how
much will they be willing to pay? General Motors expects to lose money in the
beginning and has not yet announced a price for the vehicle, but the continued
viability of the firm could depend on how fast it can sell the new cars and at what
price. The company is banking on tax credits, enacted this year by Congress, to
encourage people to buy plug-in hybrids, and high petrol prices would help as
well.
But the firm's chief economist Mustafa Mohatarem says that he can't help but
wonder whether consumer demand for electric vehicles has been exaggerated. "It
is critically dependent on the battery," he says. "Until you have a much better
handle on the cost of this technology, to talk about demand is in a sense
ridiculous."
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Have we forgotten something?
Others look at the market and see a different problem: a lack of batteries.
Charles Gassenheimer, chief executive of Ener1 Group, a company in New York
that produces lithium batteries, says that car manufacturers have collectively
announced some 75 types of electric cars that are supposed to hit the road by
2013. But they have been slow to commit to orders, he says. And without orders,
battery manufacturers can't invest the time and money necessary to ramp up
production, a bottleneck that could delay the roll-out of new vehicles.
Governments seeking to spur the electric-car market must look at battery
manufacturing in addition to consumers and car manufacturers, Gassenheimer
says. "There needs to be some government intervention at this phase in the
game. Otherwise it's going to be a chicken-and-egg problem that doesn't get
solved."
Gassenheimer also raises concerns that countries such as the United States will
simply trade their dependence on Middle Eastern oil for a reliance on Asian
batteries. He has a sizeable stake in the outcome, of course, but the issue has
political resonance as governments look to spur new green jobs. Experts say that
Ener1 and other Western companies have the technology, but Asian companies
have a leg-up on the manufacturing side simply because Asia has such a lead in
producing lithium-ion batteries for electronics.
"The United States is certainly not being blindsided at this time, but whether or
not we really have the resources and critical mass to compete in the long term in
automotive batteries is still very much an open question," says Yet-Ming Chiang,
a materials scientist at the Massachusetts Institute of Technology in Cambridge,
and founder of lithium-battery manufacturer A123Systems in Watertown,
Massachusetts. "The same thing goes for Europe."
“We have some time to look at the next mega-application, and the next
mega-application is the automotive industry.”
Soonho Ahn
Others dismiss concerns about where the batteries are going to be made, citing a
crucial difference between electronics and vehicles: electronics are by and large
made in Asia, but cars are made in the West, too. Building batteries near
automobile plants would not only save money, it would also get around complex
international shipping regulations that put lithium-ion batteries in the 'dangerous
goods' category. The market "is driven by where the end product is", says Khalil
Amine, a battery researcher and one of Hillebrand's colleagues at Argonne. "For
electronics, we buy everything from Asia. For transportation, there is plenty of
production here."
General Motors tested lithium batteries from every manufacturer it could find and
narrowed the decision down to two companies: A123Systems and LG Chem, a
Korean giant that made its name in electronics. Only in late October did the
contract reportedly go to LG Chem, which has a stronger base and a longer
history on the manufacturing side. LG Chem has already partnered with the
Korean car manufacturer Hyundai to supply 7,000–10,000 lithium-battery packs
for a pair of hybrid vehicles that will begin rolling off the line in 2009.
Soonho Ahn, LG Chem's vice-president for battery research and development,
says that his company isn't expecting to make money on its automotive batteries
for some time but wants to be ready when the market takes off. He notes that
the battery market in Asia is in "equilibrium" after several years of stiff
competition in the electronics sector. "We have some time to look at the next
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mega-application, and the next mega-application is the automotive industry," he
says. "We're pretty sure that the market is coming."
Making connections
So what will the market be like when it does come? Plug-in hybrids such as the
Volt represent a leap beyond battery-augmented cars that merely make better
use of petrol. They also give drivers the freedom to run on electricity for short
trips while still making long trips, albeit guzzling gas on the way. But some car
manufacturers say that the best path forward would be an all-electric vehicle,
which could one day all but eliminate oil consumption in the transportation sector.
Getting rid of the petrol motor greatly lessens costs and complexity and opens up
space for more battery power. "In terms of a solution, both from a carbon dioxide
point of view and from a technical point of view, the hybrid and the plug-in hybrid
do not provide the technical breakthrough that the electric vehicle could provide,"
says Serge Yoccoz, who is in charge of electric vehicles at Renault. "And from
what we've seen, the plug-in hybrid is definitely more expensive [than an electric
car would be], even if you take into account the need to develop a charging
infrastructure."
So while researchers search for the technical breakthrough, entrepreneurs are
trying to get around the high costs by rethinking the way we market cars,
batteries and ultimately energy.
Click for larger image.
One such innovator, Better Place of Palo Alto, California, is aiming for nothing
short of a wholesale conversion of the transportation sector. The company likens
itself to a cell-phone network for all-electric cars: you buy the car from a Better
Place partner and then sign up for one of its various user plans. Better Place then
provides a network of charging spots — at home, work and retail outlets — as
well as stations at which used battery packs could be swapped for recharged ones
by a robotic arm in a matter of minutes (see graphic, right).
But to accomplish all this, Better Place needs a computer system that can track
electricity charges wherever they are incurred. It also needs to partner with
governments and industry, including the automotive, battery and utility sectors.
So far, Better Place has lined up partnerships with an alliance between Nissan and
Renault to pursue electric cars, and the company plans to roll out its system in
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Israel, Denmark, Australia and California, with the first deployments scheduled
for 2010.
The scheme is ambitious, but Sidney Goodman, head of automotive alliances at
Better Place, says that's the only way to do it. "We don't believe we can do this
on a small scale. It's one of these projects where either you do it big or you don't
do it".
Better Place is aiming to provide family sedans that have a 160-kilometre range
in an effort to attract all drivers, not just city commuters with an environmental
bent. Goodman runs through some rough numbers — assuming that a battery
costs US$15,000 (which is likely to be on the high end of the scale, he stresses),
an electric vehicle would cost about 6 cents per kilometre to power. That
compares with just under 12 cents per kilometre for conventional cars in the
United States, and twice that in Europe.
A Norwegian company called Th!nk is taking a similar route with its all-electric
commuter car, which is due to hit roads in Norway, Denmark and Sweden in
coming months. With an initial price tag of about 200,000 Norwegian krone
($30,000), the car will cost about 20% more than the same-sized petrol-powered
car and will drive some 180 kilometres on a charge. Customers then pay a
monthly lease to cover the cost of electricity and the battery. "We'll get the costs
of our car down to somewhat similar to the cost of a petrol-powered car, and
then we'll have a very strong proposition going forwards," says Richard Canny,
Th!nk's chief executive.
Tapping the matrix
Utility firms are eager to cooperate. Although making electric vehicles a reality
will require unprecedented cooperation between two industries that have until
now had little in common, utilities actually see many more benefits than
headaches. The fundamental fact is that most of the charging would take place at
night, which creates a new source of revenue at a time when utilities typically
have excess capacity.
In the end, this should translate into substantial reductions in greenhouse-gas
emissions, even in countries such as the United States that get much of their
electricity from coal. A plug-in hybrid running on electricity generated entirely
from coal is roughly equivalent to a conventional hybrid in terms of emissions,
but utilities say that in the early years, electric vehicles will frequently draw
power from spare generating capacity that uses cleaner-burning natural gas.
Scaled up, millions of batteries — either in cars or in a future after-market for
used batteries — could provide utilities with a flexible storage system that could
soak up renewable power, particularly from wind turbines at night.
Assuming that plug-in hybrids will make up 60% of the US automobile market in
2050, electric transport would consume as little as 8% of the nation's electricity,
according to a joint modelling study conducted in 2007 by the Electric Power
Research Institute — a non-profit research organization in Palo Alto — and the
Natural Resources Defense Council, an environmental advocacy group based in
New York. The resulting report, The Power to Reduce CO2 Emissions, predicts that
the nation would use 15–20% less oil and reduce its greenhouse-gas emissions
by 450 million tonnes, which is akin to pulling 82.5 million internal-combustion
vehicles off the road.
"Our fundamental conclusion from this study is that the number one driver of
benefits is really the number of vehicles," says Mark Duvall, programme manager
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of electric transportation at the Electric Power Research Institute. "Don't worry
about charging them from some perfect grid of the future – just get the cars out
there. They don't have to be perfect."
Utilities such as Southern California Edison in Rosemead are already thinking
about how to integrate cars into the electricity system, allowing them to charge
up at work or park in 'smart garages' that coordinate activities between the car
and the grid. In the early days, advanced charging equipment would
communicate with the utility to time the charging so that everybody's vehicle is
fully juiced when it needs to be — but not necessarily before. That would help
ensure that millions of vehicles don't create a sudden surge on the electricity
system when people return from work, when they also tend to turn on lights and
crank up their appliances. Further out, this process could be reversed, allowing
batteries to provide power to the grid when it is needed most — so long as they
are fully charged when it comes to time to drive.
ADVERTISEMENT
Levelling out the daily demand cycles would allow utilities to manage the grid
more efficiently, potentially lowering costs to consumers. "The more cars that
come onto the energy system, the better off it is for the energy system," says Ed
Kjaer, director of electric transportation for Southern California Edison. And Kjaer
says that the vehicles will become cleaner over time as utilities expand their
renewable electricity offerings.
That kind of logic has convinced many researchers that electric cars are a must if
the planet is to deal with global warming, even if they ultimately raise the stakes
on efforts to produce carbon-free electricity. "We've got to electrify the
transportation system and then clean up the grid," says Timothy Lipman,
research director at the University of California's Transportation Sustainability
Research Center in Berkeley. "It's the easiest path."
See Editorial, page 421
See also Correspondence: Choosing between batteries or biomass to stay on
the road
Comments
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
Very interesting article on electric vehicles. Too bad that the clunky looking Chevy
Volt was the head-liner. It still has an internal combustion engine! Not one mention of an
all-electric, 200 mile range vehicle that is already on the road - the Tesla Roadster, soon
to be followed by the White Star Sedan - from the same company in San Carlos California!
Imagine if that company got some additional financing from the government to move
more rapidly into the general market, and out of the expensive boutique market. Their
slick looking electrics would be common place on the daily commuter trip! And this would
be going on without all of the dripping oil, fluids, and crap into the air. It is easier to
control pollution at the stationary source of electric generation than on a billion mobile
polluting units called cars. One of many obstacles to getting that block of oil burning
metal out of American cars - the UAW! Just think for a moment: Making a vehicle with 5
moving parts that runs on electricity as opposed to making internal combustion engines
and drive-line with hundreds of parts would eliminate a lot of union jobs! What about the
after market racket on spare parts? I believe that much innovation in our auto industry
has been stifled by a union strangle-hold, and that there has been little incentive to
change the status quo. Electrics won't replace the heavy lifting to be done by trucks, but
as an alternative to the millions of folks sitting in their 6,000 lb. 20 ft. long SUVs, the
daily commute in an electric makes some sense for me. Soarhead
o
Report this comment
o
01 Dec, 2008
o
Posted by: Gary Filice
Published online 13 August 2008 | Nature 454, 816-823 (2008) | doi:10.1038/454816a
News Feature
Energy alternatives:
Electricity without carbon
Quirin Schiermeier , Jeff Tollefson , Tony Scully , Alexandra Witze & Oliver Morton
This article is best viewed as a PDF.
Electricity generation provides 18,000 terawatt-hours of energy a year,
around 40% of humanity's total energy use. In doing so it produces more
than 10 gigatonnes of carbon dioxide every year, the largest sectoral
contribution of humanity's fossil-fuel derived emissions. Yet there is a
wide range of technologies — from solar and wind to nuclear and
geothermal — that can generate electricity without net carbon emissions
from fuel.
The easiest way to cut the carbon released by electricity generation is to
increase efficiency. But there are limits to such gains, and there is the
familiar paradox that greater efficiency can lead to greater consumption.
So a global response to climate change must involve a move to carbonfree sources of electricity. This requires fresh thinking about the price of
carbon, and in some cases new technologies; it also means new
transmission systems and smarter grids. But above all, the various
sources of carbon-free generation need to be scaled up to power an
increasingly demanding world. In this special feature, Nature's News
team looks at how much carbon-free energy might ultimately be
available — and which sources make most sense.
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Hydropower
J. TAYLOR
The world has a lot of dams — 45,000 large ones, according to the World Energy
Council, and many more at small scales. Its hydroelectric power plants have a
generating capacity of 800 gigawatts (for a guide to power, see ‘By the numbers’),
and they currently supply almost one-fifth of the electricity consumed worldwide.
As a source of electricity, dams are second only to fossil fuels, and generate 10
times more power than geothermal, solar and wind power combined. With a
claimed full capacity of 18 gigawatts, the Three Gorges dam in China can
generate more or less twice as much power as all the world's solar cells. An
additional 120 gigawatts of capacity is under development.
One reason for hydropower's success is that it is a widespread resource — 160
countries use hydropower to some extent. In several countries hydropower is the
largest contributor to grid electricity — it is not uncommon in developing
countries for a large dam to be the main generating source. Nevertheless, it is in
large industrialized nations that have big rivers that hydroelectricity is shown in
its most dramatic aspect. Brazil, Canada, China, Russia and the United States
currently produce more than half of the world's hydropower.
Cost: According to the International Hydropower Association (IHA), installation
costs are usually in the range of US$1 million to more than $5 million per
megawatt of capacity, depending on the site and size of the plant. Dams in
lowlands and those with only a short drop between the water level and the
turbine tend to be more expensive; large dams are cheaper per watt of capacity
than small dams in similar settings. Annual operating costs are low — 0.8–2% of
capital costs; electricity costs $0.03–0.10 per kilowatt-hour, which makes dams
competitive with coal and gas.
Capacity: The absolute limit on hydropower is the rate at which water flows
downhill through the world's rivers, turning potential energy into kinetic energy
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as it goes. The amount of power that could theoretically be generated if all the
world's run-off were 'turbined' down to sea level is more than 10 terawatts.
However, it is rare for 50% of a river's power to be exploitable, and in many
cases the figure is below 30%.
Those figures still offer considerable opportunity for new capacity, according to
the IHA. Europe currently sets a benchmark for hydropower use, with 75% of
what is deemed feasible already exploited. For Africa to reach the same level, it
would need to increase its hydropower capacity by a factor of 10 to more than
100 gigawatts. Asia, which already has the greatest installed capacity, also has
the greatest growth potential. If it were to triple its generating capacity, thus
harnessing a near-European fraction of its potential, it would double the world's
overall hydroelectric capacity. The IHA says that capacity could triple worldwide
with enough investment.
Advantages: The fact that hydroelectric systems require no fuel means that they
also require no fuel-extracting infrastructure and no fuel transport. This means
that a gigawatt of hydropower saves the world not just a gigawatt's worth of coal
burned at a fossil-fuel plant, but also the carbon costs of mining and transporting
that coal. As turning on a tap is easy, dams can respond almost instantaneously
to changing electricity demand independent of the time of day or the weather.
This ease of turn-on makes them a useful back-up to less reliable renewable
sources. That said, variations in use according to need and season mean that
dams produce about half of their rated power capacity.
Hydroelectric systems are unique among generating systems in that they can, if
correctly engineered, store the energy generated elsewhere, pumping water
uphill when energy is abundant. The reservoirs they create can also provide water
for irrigation, a way to control floods and create amenities for recreational use.
Disadvantages: Not all regions have large hydropower resources — the Middle
East, for example, is relatively deficient. And reservoirs take up a lot of space;
today the area under man-made lakes is as large as two Italys. The large dams
and reservoirs that account for most of that area and for more than 90% of
hydro-generated electricity worldwide require lengthy and costly planning and
construction, as well as the relocation of people from the reservoir area. In the
past few decades, millions of people have been relocated in India and China.
Dams have ecological effects on the ecosystems upstream and downstream, and
present a barrier to migrating fish. Sediment build-up can shorten their operating
life, and sediment trapped by the dam is denied to those downstream. Biomass
that decomposes in reservoirs releases methane and carbon dioxide, and in some
cases these emissions can be of a similar order of magnitude to those avoided by
not burning fossil fuels. Climate change could itself limit the capacity of dams in
some areas by altering the amount and pattern of annual run-off from sources
such as the glaciers of Tibet.
Because hydro is a mature technology, there is little room for improvement in the
efficiency of generation. Also, the more obvious and easy locations have been
used, and so the remaining potential can be expected to be harder to exploit.
Small (less than 10 megawatts) 'run-of-river' schemes that produce power from
the natural flow of water — as millers have been doing for four millennia — are
appealing, as they have naturally lower impacts. However, they are about five
times more expensive and harder to scale than larger schemes.
Verdict: A cheap and mature technology, but with substantial environmental
costs; roughly a terawatt of capacity could be added.
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Nuclear fission
J. TAYLOR
When reactor 4 at the Chernobyl nuclear power plant in Ukraine melted down on
26 April 1986, the fallout contaminated large parts of Europe. That disaster, and
the earlier incident at Three Mile Island in Pennsylvania, blighted the nuclear
industry in the West for a generation. Worldwide, though, the picture did not
change quite as dramatically.
In 2007, 35 nuclear plants were under construction, almost all in Asia. The 439
reactors already in operation had an overall capacity of 370 gigawatts, and
contributed around 15% of the electricity generated worldwide, according to the
most recent figures from the International Atomic Energy Agency (IAEA), which
serves as the world's nuclear inspectorate.
Costs: Depending on the design of the reactor, the site requirements and the
rate of capital depreciation, the light-water reactors that make up most of the
world's nuclear capacity produce electricity at costs of between US$0.025 and
$0.07 per kilowatt-hour. The technology that makes this possible has benefited
from decades of expensive research, development and purchases subsidized by
governments; without that boost it is hard to imagine that nuclear power would
currently be in use.
Capacity: Because nuclear power requires fuel, it is constrained by fuel stocks.
There are some 5.5 million tonnes of uranium in known reserves that could
profitably be extracted at a cost of US$130 per kilogram or less, according to the
latest edition of the 'Red Book', in which the IAEA and the Organisation for
Economic Co-operation and Development (OECD) assess uranium resources. At
the current use of 66,500 tonnes per year, that is about 80 years' worth of fuel.
The current price of uranium is over that $130 threshold.
Geologically similar ore deposits that are as yet unproven — 'undiscovered
reserves' — are thought to amount to roughly double the proven reserves, and
lower-grade ores offer considerably more. Uranium is not a particularly rare
element — it is about as common a constituent of Earth's crust as zinc. Estimates
of the ultimate recoverable resource vary greatly, but 35 million tonnes might be
considered available. Nor is uranium the only naturally occurring element that can
be made into nuclear fuel. Although they have not yet been developed, thoriumfuelled reactors are a possibility; bringing thorium into play would double the
available fuel reserves.
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Furthermore, although current reactor designs use their fuel only once, this could
be changed. Breeder reactors, which make plutonium from uranium isotopes that
are not themselves useful for power production, can effectively create more fuel
than they use. A system built on such reactors might get 60 times more energy
out for every kilogram of natural uranium put in, although lower multiples might
be more realistic.
With breeder reactors, which have yet to be proven on a commercial basis, the
world could in principle go 100% nuclear. Without them, it is still plausible for the
amount of nuclear capacity to grow by a factor of two or three, and to operate at
that level for a century or more.
Advantages: Nuclear power has relatively low fuel costs and can run at full blast
almost constantly — US plants deliver 90% of their rated capacity. This makes
them well suited to providing always-on 'baseload' power to national grids.
Uranium is sufficiently widespread that the world's nuclear-fuel supply is unlikely
to be threatened by political factors.
Disadvantages: There is no agreed solution to the problem of how to deal with
the nuclear waste that has been generated in nuclear plants over the past 50
years. Without long-term solutions, which are more demanding politically than
technically, growth in nuclear power is an understandably hard sell. A further
problem is that the spread of nuclear power is difficult to disentangle from the
proliferation of nuclear weapons capabilities. Fuel cycles that involve recycling,
and which thus necessarily produce plutonium, are particularly worrying. Even
without proliferation worries, nuclear power stations may make tempting targets
for terrorists or enemy forces (although in the latter case the same is true of
hydroelectric plants).
A long-term commitment to greatly increased use of nuclear power would require
public acceptance not just of existing technologies but of new ones, too —
thorium and breeder reactors, for instance. These technologies would also have
to win over investors and regulators (for nuclear fusion, see ‘Farther out’).
Nuclear power is also extremely capital intensive; power costs over the life of the
plant are comparatively low only because the plants are long lived. Nuclear power
is thus an expensive option in the short term. Another constraint may be a lack of
skilled workers. Building and operating nuclear plants requires a great many
highly trained professionals, and enlarging this pool of talent enough to double
the rate at which new plants are brought online might prove very challenging.
The engineering capacity for making key components would also need enlarging.
In light of these obstacles, predictions of the future role of nuclear power vary
considerably. The European Commission's World Energy Technology Outlook —
2050 contains a bullish scenario that assumes that, with public acceptance and
the development of new reactor technologies, nuclear power could provide about
1.7 terawatts by 2050. The IAEA's analysts are more cautious. Hans-Holger
Rogner, head of the agency's planning and economic study section, sees capacity
rising to not more than 1,200 gigawatts by 2050. An interdisciplinary study
carried out in 2003 by the Massachusetts Institute of Technology described a
concrete scenario for tripling capacity to 1,000 gigawatts by 2050, a scenario
predicated on US leadership, continued commitment by Japan and renewed
activity by Europe. This scenario relied only on improved versions of today's
reactors rather than on any radically different or improved design.
Verdict: Reaching a capacity in the terawatt range is technically possible over
the next few decades, but it may be difficult politically. A climate of opinion that
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came to accept nuclear power might well be highly vulnerable to adverse events
such as another Chernobyl-scale accident or a terrorist attack.
Biomass
J. TAYLOR
Biomass was humanity's first source of energy, and until the twentieth century it
remained the largest; even today it comes second only to fossil fuels. Wood, crop
residues and other biological sources are an important energy source for more
than two billion people. Mostly, this fuel is burned in fires and cooking stoves, but
over recent years biomass has become a source of fossil-fuel-free electricity. As
of 2005, the World Energy Council estimates biomass generating capacity to be at
least 40 gigawatts, larger than any renewable resource other than wind and
hydropower. Biomass can supplement coal or in some cases gas in conventional
power plants. Biomass is also used in many co-generation plants that can capture
85–90% of the available energy by making use of waste heat as well as electric
power.
Costs: The price of biomass electricity varies widely depending on the availability
and type of the fuel and the cost of transporting it. Capital costs are similar to
those for fossil-fuel plants. Power costs can be as little as $0.02 per kilowatt-hour
when biomass is burned with coal in a conventional power plant, but increase to
$0.03–0.05 per kilowatt-hour from a dedicated biomass power plant. Costs
increase to $0.04–0.09 per kilowatt-hour for a co-generation plant, but recovery
and use of the waste heat makes the process much more efficient. The biggest
problem for new biomass power plants is finding a reliable and concentrated
feedstock that is available locally; keeping down transportation costs means
keeping biomass power plants tied to locally available fuel and quite small, which
increases the capital cost per megawatt.
Capacity: Biomass is limited by the available land surface, the efficiency of
photosynthesis, and the supply of water. An OECD round table in 2007 estimated
that there is perhaps half a billion hectares of land not in agricultural use that
would be suitable for rain-fed biomass production, and suggested that by 2050
this land, plus crop residues, forest residues and organic waste might provide
enough burnable material each year to provide 68,000 terawatt-hours. Converted
to electricity at an efficiency of 40%, that could provide a maximum of 3
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terawatts. The Intergovernmental Panel on Climate Change pegs the potential at
roughly 120,000 terawatt-hours in 2050, which equates to slightly more than 5
terawatts on the basis of a larger estimate of available land.
These projections involve some fairly extreme assumptions about converting land
to the production of energy crops. And even to the extent that these assumptions
prove viable, electricity is not the only potential use for such plantations. By
storing solar energy in the form of chemical bonds, biomass lends itself better
than other renewable energy resources to the production of fuel for
transportation (see page 841). Although turning biomass to biofuel is not as
efficient as just burning the stuff, it can produce a higher-value product. Biofuels
might easily beat electricity generation as a use for biomass in most settings.
Advantages: Plants are by nature carbon-neutral and renewable, although
agriculture does use up resources, especially if it requires large amounts of
fertilizer. The technologies needed to burn biomass are mature and efficient,
especially in the case of co-generation. Small systems using crop residues can
minimize transportation costs.
If burned in power plants fitted with carbon-capture-and-storage hardware,
biomass goes from being carbon neutral to carbon negative, effectively sucking
carbon dioxide out of the atmosphere and storing it in the ground (see 'Carbon
capture and storage'). This makes it the only energy technology that can actually
reduce carbon dioxide levels in the atmosphere. As with coal, however, there are
costs involved in carbon capture, both in terms of capital set-up and in terms of
efficiency.
Disadvantages: There is only so much land in the world, and much of it will be
needed to provide food for the growing global population. It is not clear whether
letting market mechanisms drive the allocation of land between fuel and food is
desirable or politically feasible. Changing climate could itself alter the availability
of suitable land. There is likely to be opposition to increased and increasingly
intense cultivation of energy crops. Use of waste and residues may remove
carbon from the land that would otherwise have enriched the soil; long-term
sustainability may not be achievable.
Bioenergy dependence could also open the doors to energy crises caused by
drought or pestilence, and land-use changes can have climate effects of their own:
clearing land for energy crops may produce emissions at a rate the crops
themselves are hard put to offset.
Verdict: If a large increase in energy crops proves acceptable and sustainable,
much of it may be used up in the fuel sector. However, small-scale systems may
be desirable in an increasing number of settings, and the possibility of carbonnegative systems — which are plausible for electricity generation but not for
biofuels — is a unique and attractive capability.
Wind
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J. TAYLOR
Wind power is expanding faster than even its fiercest advocates could have
wished a few years ago. The United States added 5.3 gigawatts of wind capacity
in 2007 — 35% of the country's new generating capacity — and has another 225
gigawatts in the planning stages. There is more wind-generating capacity being
planned in the United States than for coal and gas plants combined. Globally,
capacity has risen by nearly 25% in each of the past five years, according to the
Global Wind Energy Council.
Wind Power Monthly estimates that the world's installed capacity for wind as of
January 2008 was 94 gigawatts. If growth continued at 21%, that figure would
triple over six years.
Despite this, the numbers remain small on a global scale, especially given that
wind farms have historically generated just 20% of their capacity.
Costs: Installation costs for wind power are around US$1.8 million per megawatt
for onshore developments and between $2.4 million and $3 million for offshore
projects. That translates to $0.05–0.09 per kilowatt-hour, making wind
competitive with coal at the lower end of the range. With subsidies, as enjoyed in
many countries, the costs come in well below those for coal — hence the boom.
The main limit on wind-power installation at the moment is how fast
manufacturers can make turbines.
These costs represent significant improvements in the technology. In 1981, a
wind farm might have consisted of an array of 50-kilowatt turbines that produced
power for roughly $0.40 per kilowatt-hour. Today's turbines can produce 30 times
as much power at one-fifth the price with much less down time.
Capacity: The amount of energy generated by the movement of Earth's
atmosphere is vast — hundreds of terawatts. In a 2005 paper, a pair of
researchers from Stanford University calculated that at least 72 terawatts could
be effectively generated using 2.5 million of today's larger turbines placed at the
13% of locations around the world that have wind speeds of at least 6.9 metres
per second and are thus practical sites (C. L. Archer and M. Z. Jacobson J.
Geophys. Res. 110, D12110; 2005).
Advantages: The main advantage of wind is that, like hydropower, it doesn't
need fuel. The only costs therefore come from building and maintaining the
turbines and power lines. Turbines are getting bigger and more reliable. The
development of technologies for capturing wind at high altitudes could provide
sources with small footprints capable of generating power in a much more
sustained way.
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Disadvantages: Wind's ultimate limitation might be its intermittency. Providing
up to 20% of a grid's capacity from wind is not too difficult. Beyond that, utilities
and grid operators need to take extra steps to deal with the variability. Another
grid issue, and one that is definitely limiting in the near term, is that the windiest
places are seldom the most populous, and so electricity from the wind needs
infrastructure development — especially for offshore settings.
Average power of the world's
winds during the boreal winter (top) and summer. The recoupable energy
is some two orders of magnitude lower because of turbine spacing and
engineering constraints. Courtesy: W. T. Liu et al. Geophys. Res. Lett. 35,
L13808 (2008).
As well as being intermittent, wind power is, like other renewable energy sources,
inherently quite low density. A large wind farm typically generates a few watts
per square metre — 10 is very high. Wind power thus depends on cheap land, or
on land being used for other things at the same time, or both. It is also hard to
deploy in an area where the population sets great store by the value of a turbinefree landscape.
Wind power is also unequally distributed: it favours nations with access to windy
seas and their onshore breezes or great empty plains. Germany has covered
much of its windiest land with turbines, but despite these pioneering efforts, its
combined capacity of 22 GW supplies less than 7% of the country's electricity
needs. Britain, which has been much slower to adopt wind power, has by far the
largest offshore potential in Europe — enough to meet its electricity needs three
times over, according to the British Wind Energy Association. Industry estimates
suggest that the European Union could meet 25% of its current electricity needs
by developing less than 5% of the North Sea.
Such truly large-scale deployment of wind-power schemes could affect local, and
potentially global, climate by altering wind patterns, according to research by
David Keith, head of the Energy and Environmental Systems Group at the
University of Calgary in Canada. Wind tends to cool things down, so temperatures
around a very large wind farm could rise as turbines slow the wind to extract its
energy. Keith and his team suggest that 2 TW of wind capacity could affect
temperatures by about 0.5 °C, with warming at mid-latitudes and cooling at the
poles — perhaps in that respect offsetting the effect of global warming (D. W.
Keith et al. Proc. Natl Acad. Sci. USA 101, 16115–16120; 2004).
Verdict: With large deployments on the plains of the United States and China,
and cheaper access to offshore, a wind-power capacity of a terawatt or more is
plausible.
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Geothermal
J. TAYLOR
Earth's interior contains vast amounts of heat, some of it left over from the
planet's original coalescence, some of it generated by the decay of radioactive
elements. Because rock conducts heat poorly, the rate at which this heat flows to
the surface is very slow; if it were quicker, Earth's core would have frozen and its
continents ceased to drift long ago.
The slow flow of Earth's heat makes it a hard resource to use for electricity
generation except in a few specific places, such as those with abundant hot
springs. Only a couple of dozen countries produce geothermal electricity, and only
five of those — Costa Rica, El Salvador, Iceland, Kenya and the Philippines —
generate more than 15% of their electricity this way. The world's installed
geothermal electricity capacity is about 10 gigawatts, and is growing only slowly
— about 3% per year in the first half of this decade. A decade ago, geothermal
capacity was greater than wind capacity; now it is almost a factor of ten less.
Earth's heat can also be used directly. Indeed, small geothermal heat pumps that
warm houses and businesses directly may represent the greatest contribution
that Earth's warmth can make to the world's energy budget.
Costs: The cost of a geothermal system depends on the geological setting.
Jefferson Tester, a chemical engineer who was part of a team that produced an
influential Massachusetts Institute of Technology (MIT) report on geothermal
technology in 2006, explains the situation as being “similar to mineral resources.
There is a continuum of resource grades — from shallow, high-temperature
regions of high-porosity rock, to deeper low-porosity regions that are more
challenging to exploit”. That report put the cost of exploiting the best sites —
those with a lot of hot water circulating close to the surface — at about US$0.05
per kilowatt-hour. Much more abundant low-grade resources are exploitable with
current technology only at much higher prices.
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Absolute capacity: Earth loses heat at between 40 TW and 50 TW a year, which
works out at an average of a bit less than a tenth of a watt per square metre. For
comparison, sunlight comes in at an average of 200 watts per square metre. With
today's technology, 70 GW of the global heat flux is seen as exploitable. With
more advanced technologies, at least twice that could be used. The MIT study
suggested that using enhanced systems that inject water at depth using
sophisticated drilling systems, it would be possible to set up 100 GW of
geothermal electricity in the United States alone. With similar assumptions a
global figure of a terawatt or so can be reached, suggesting that geothermal
could, with a great deal of investment, provide as much electricity as dams do
today.
Advantages: Geothermal resources require no fuel. They are ideally suited to
supplying base-load electricity, because they are driven by a very regular energy
supply. At 75%, geothermal sources boast a higher capacity factor than any other
renewable. Low-grade heat left over after generation can be used for domestic
heating or for industrial processes.
Surveying and drilling previously unexploited geothermal resources has become
much easier thanks to mapping technology and drilling equipment designed by
the oil industry. A significant technology development programme — Tester
suggests $1 billion over 10 years — could greatly expand the achievable capacity
as lower-grade resources are opened up.
Disadvantages: High-grade resources are quite rare, and even low-grade
resources are not evenly distributed. Carbon dioxide can leak out of some
geothermal fields, and there can be contamination issues; the water that brings
the heat to the surface can carry compounds that shouldn't be released into
aquifers. In dry regions, water availability can be a constraint. Large-scale
exploitation requires technologies that, although plausible, have not been
demonstrated in the form of robust, working systems.
Verdict: Capacity might be increased by more than an order of magnitude.
Without spectacular improvements, it is unlikely to outstrip hydro and wind and
reach a terawatt.
Solar
J. TAYLOR
Not to take anything away from the miracle of photosynthesis, but even under
the best conditions plants can only turn about 1% of the solar radiation that hits
their surfaces into energy that anyone else can use. For comparison, a standard
commercial solar photovoltaic panel can convert 12–18% of the energy of
sunlight into useable electricity; high-end models come in above 20% efficiency.
Increasing manufacturing capacity and decreasing costs have led to remarkable
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growth in the industry over the past five years: in 2002, 550 MW of cells were
shipped worldwide; in 2007 the figure was six times that. Total installed solar-cell
capacity is estimated at 9 GW or so. The actual amount of electricity generated,
though, is considerably less, as night and clouds decrease the power available. Of
all renewables, solar currently has the lowest capacity factor, at about 14%.
Solar cells are not the only technology by which sunlight can be turned into
electricity. Concentrated solar thermal systems use mirrors to focus the Sun's
heat, typically heating up a working fluid that in turn drives a turbine. The mirrors
can be set in troughs, in parabolas that track the Sun, or in arrays that focus the
heat on a central tower. As yet, the installed capacity is quite small, and the
technology will always remain limited to places where there are a lot of cloud-free
days — it needs direct sun, whereas photovoltaics can make do with more diffuse
light.
Costs: The manufacturing cost of solar cells is currently US$1.50–2.50 for a
watt's worth of generating capacity, and prices are in the $2.50–3.50 per watt
range. Installation costs are extra; the price of a full system is normally about
twice the price of the cells. What this means in terms of cost per kilowatt-hour
over the life of an installation varies according to the location, but it comes out at
around $0.25–0.40. Manufacturing costs are dropping, and installation costs will
also fall as photovoltaic cells integrated into building materials replace freestanding panels for domestic applications. Current technologies should be
manufacturing at less than $1 per watt within a few years (see Nature 454, 558–
559; 2008).
The cost per kilowatt-hour of concentrated solar thermal power is estimated by
the US National Renewable Energy Laboratory (NREL) in Golden, Colorado, at
about $0.17.
Capacity: Earth receives about 100,000 TW of solar power at its surface —
enough energy every hour to supply humanity's energy needs for a year. There
are parts of the Sahara Desert, the Gobi Desert in central Asia, the Atacama in
Peru or the Great Basin in the United States where a gigawatt of electricity could
be generated using today's photovoltaic cells in an array 7 or 8 kilometres across.
Theoretically, the world's entire primary energy needs could be served by less
than a tenth of the area of the Sahara.
Advocates of solar cells point to a calculation by the NREL claiming that solar
panels on all usable residential and commercial roof surfaces could provide the
United States with as much electricity per annum as the country used in 2004. In
more temperate climes things are not so promising: in Britain one might expect
an annual insolation of about 1,000 kilowatt-hours per metre on a south-facing
panel tilted to take account of latitude: at 10% efficiency, that means more than
60 square metres per person would be needed to meet current UK electricity
consumption.
Advantages: The Sun represents an effectively unlimited supply of fuel at no
cost, which is widely distributed and leaves no residue. The public accepts solar
technology and in most places approves of it — it is subject to less geopolitical,
environmental and aesthetic concern than nuclear, wind or hydro, although
extremely large desert installations might elicit protests.
Photovoltaics can often be installed piecemeal — house by house and business by
business. In these settings, the cost of generation has to compete with the retail
price of electricity, rather than the cost of generating it by other means, which
gives solar a considerable boost. The technology is also obviously well suited to
off-grid generation and thus to areas without well developed infrastructure.
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Both photovoltaic and concentrated solar thermal technologies have clear room
for improvement. It is not unreasonable to imagine that in a decade or two new
technologies could lower the cost per watt for photovoltaics by a factor of ten,
something that is almost unimaginable for any other non-carbon electricity source.
Disadvantages: The ultimate limitation on solar power is darkness. Solar cells
do not generate electricity at night, and in places with frequent and extensive
cloud cover, generation fluctuates unpredictably during the day. Some
concentrated solar thermal systems get around this by storing up heat during the
day for use at night (molten salt is one possible storage medium), which is one of
the reasons they might be preferred over photovoltaics for large installations.
Another possibility is distributed storage, perhaps in the batteries of electric and
hybrid cars (see page 810).
Another problem is that large installations will usually be in deserts, and so the
distribution of the electricity generated will pose problems. A 2006 study by the
German Aerospace Centre proposed that by 2050 Europe could be importing 100
GW from an assortment of photovoltaic and solar thermal plants across the
Middle East and North Africa. But the report also noted that this would require
new direct-current high-voltage electricity distribution systems.
A possible drawback of some advanced photovoltaic cells is that they use rare
elements that might be subject to increases in cost and restriction in supply. It is
not clear, however, whether any of these elements is either truly constrained —
more reserves might be made economically viable if demand were higher — or
irreplaceable.
Verdict: In the middle to long run, the size of the resource and the potential for
further technological development make it hard not to see solar power as the
most promising carbon-free technology. But without significantly enhanced
storage options it cannot solve the problem in its entirety.
Ocean energy
J. TAYLOR
The oceans offer two sorts of available kinetic energy — that of the tides and that
of the waves. Neither currently makes a significant contribution to world
electricity generation, but this has not stopped enthusiasts from developing
schemes to make use of them. There are undoubtedly some places where, thanks
to peculiarities of geography, tides offer a powerful resource. In some situations
that potential would best be harnessed by a barrage that creates a reservoir not
unlike that of a hydroelectric dam, except that it is refilled regularly by the pull of
the Moon and the Sun, rather than being topped up slowly by the runoff of falling
rain. But although there are various schemes for tidal barrages under discussion
— most notably the Severn Barrage between England and Wales, which
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proponents claim could offer as much as 8 GW — the plant on the Rance estuary
in Brittany, rated at 240 MW, remains the world's largest tidal-power plant more
than 40 years after it came into use.
There are also locations well suited to tidal-stream systems — submerged
turbines that spin in the flowing tide like windmills in the air. The 1.2 MW turbine
installed this summer in the mouth of Strangford Lough, Northern Ireland, is the
largest such system so far installed.
Most technologies for capturing wave power remain firmly in the testing phase.
Individual companies are working through an array of potential designs, including
machines that undulate on waves like a snake, bob up and down as water passes
over them, or nestle on the coastline to be regularly overtopped by waves that
power turbines as the water drains off. The European Marine Energy Centre's test
bed off the United Kingdom's Orkney Islands, where manufacturers can hook up
prototypes to a marine electricity grid and test how well they withstand the
pounding waves, is a leading centre of research. Pelamis Wave Power, a company
based in Edinburgh, UK, for instance, has moved from testing there to installing
three machines off the coast of Portugal, which together will eventually generate
2.25 MW.
Costs: Barrage costs differ markedly from site to site, but are broadly
comparable to costs for hydropower. At an estimated cost of £15 billion (US$30
billion) or more, the capital costs of the Severn Barrage would be about $4 million
per megawatt. A 2006 report from the British Carbon Trust, which spurs
investment in non-carbon energy, puts the costs of tidal-stream electricity in the
$0.20–0.40 per kilowatt-hour range, with wave systems running up to $0.90 per
kilowatt-hour. Neither technology is anywhere close to the large-scale production
needed to significantly drive such costs down.
Capacity: The interaction of Earth's mass with the gravitational fields of the
Moon and the Sun is estimated to produce about 3 TW of tidal energy— rather
modest for such an astronomical source (although enough to play a key role in
keeping the oceans mixed — see Nature 447, 522–524; 2007). Of this, perhaps 1
TW is in shallow enough waters to be easily exploited, and only a small part of
that is realistically available. EDF, a French power company developing tidal
power off Brittany, says that the tidal-stream potential off France is 80% of that
available all round Europe, and yet it is still little more than a gigawatt.
The power of ocean waves is estimated at more than 100 TW. The European
Ocean Energy Association estimates that the accessible global resource is
between 1 and 10 terawatts, but sees much less than that as recoverable with
current technologies. An analysis in the MRS Bulletin in April 2008 holds that
about 2% of the world's coastline has waves with an energy density of 30 kW m −1,
which would offer a technical potential of about 500 GW for devices working at
40% efficiency. Thus even with a huge amount of development, wave power
would be unlikely to get close to the current installed hydroelectric capacity.
Advantages: Tides are eminently predictable, and in some places barrages really
do offer the potential for large-scale generation that would be significant on a
countrywide scale. Barrages also offer some built-in storage potential. Waves are
not constant — but they are more reliable than winds.
ADVERTISEMENT
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Disadvantages: The available resource varies wildly with geography; not every
country has a coastline, and not every coastline has strong tides or tidal streams,
or particularly impressive waves. The particularly hot wave sites include
Australia's west coast, South Africa, the western coast of North America and
western European coastlines. Building turbines that can survive for decades at
sea in violent conditions is tough. Barrages have environmental impacts, typically
flooding previously intertidal wetlands, and wave systems that flank long
stretches of dramatic coastline might be hard for the public to accept. Tides and
waves tend by their nature to be found at the far end of electricity grids, so
bringing back the energy represents an extra difficulty. Surfers have also been
known to object …
Verdict: Marginal on the global scale.
See Editorial, page 805.
Reported and written by Quirin Schiermeier, Jeff Tollefson, Tony Scully, Alexandra
Witze and Oliver Morton.

References
1.
2.
Key World Energy Statistics 2007 (International Energy Agency, 2007).
Hohmeyer, O. & Trittin, T. (eds) Proc. IPCC Scoping Meeting on Renewable
Energy Sources 20–25 January 2008, Lübeck, Germany (Intergovernmental Panel on
Climate Change, 2008).
3.
Smil, V. Energy in Nature and Society: General Energetics of Complex
Systems (MIT Press, 2008).
4.
Metz, B., Davidson, O., Bosch, P., Dave, R. & Meyer, L. (eds) Climate
Change 2007: Mitigation of Climate Change (Cambridge Univ. Press, 2007).
Comments
Reader comments are usually moderated after posting. If you find something offensive or
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
Thanks for much needed information on energy alternatives. Did the authors
consider the possibility of harvesting some of the 50,000 billion metric tons of Hydrogen
that the Sun discards each year in the solar wind? Until there is better evidence that CO2
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causes global warming, it may be premature to report, "So a global response to climate
change must involve a move to carbon-free sources of electricity."
http://myprofile.cos.com/manuelo09
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13 Aug, 2008
o
Posted by: O M

Excellent review of energy generation alternatives. Two quick comments. First, the
article says that hydropower is "second only to fossil fuels". It says this same thing about
biomass. Which is it? Second, in the disadvantages for hydropower, the release of
methane and CO2 from decomposing biomass is sited. I have heard this quoted from
anti-dam people before and it strikes me as a little deceptive. Are you saying that without
the dam, the biomass would *not* decompose? That's a bit like saying that the reason
leaves fall off trees is because of nearby dams. Also, it is important to note the CO2
generated by rotting vegetation was only recently pulled from the atmosphere. This is a
net zero carbon emission and is part of the normal seasonal cycle of the earth as seen in
the Keeling curve. One might even argue that a dam facilitates the removal of carbon
from the atmosphere because some of the biomass is captured as sediment which is not
released from the bottom of the catchment basin. But that's probably miniscule.
o
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14 Aug, 2008
o
Posted by: David Myer

Thanks for a great summary of energy generation pros and cons! However, I think
the debate on energy technologies misses one critical element: our behaviour as energy
users. Clearly, sustainable and carbon-free energy generation is a great goal and some
very innovative solutions are appearing. It would be equally impressive to see some of
the same enthusiasm directed toward 'energy education', or seeking ways to simply use
less. Ultimately, we will need to question the assumption that energy generation capacity
must always increase. Better to do it sooner than later. regards
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14 Aug, 2008
o
Posted by: adam steer

David: hydropower is second in terms of electricity generation capacity, while
biomass is second overall: most biomass is burned in fires and stoves, though, not used
to generate electricity Oliver Morton
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16 Aug, 2008
o
Posted by: Oliver Morton

This is an excellent review but, further to Adam's comment, we tend to
concentrate on the supply side and neglect improving energy efficiency which,
particularly in the case of housing, can have considerable health and wellbeing impacts. I
live in Christchurch, NZ, and at the current price of electricity here (ca. 8p a unit)it is
estimated that some 54 000 households out of the 386 000 in the city are affected by
'fuel poverty'(>10% of income is required to achieve adequate warmth). Improvements
in insulation etc. would give substantial social and health benefits that increasing power
generation would not deliver
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17 Aug, 2008
o
Posted by: T F J Taylor

For David Myer's question:
http://www.google.com/search?q=biomass+reservoir+decomposition+anoxic+methane
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18 Aug, 2008
o
Posted by: hank roberts

Not to belabor the point made in other postings on increasing efficiency as a
carbon-free strategy for meeting electricity demand, but there is much hard data
available on the costs and potential of this approach. Setting higher efficiency standards
for appliances, establishing building codes requiring high efficiency lighting, better
insulation so that air conditioning costs are lower and use of natural light are all examples
of how we can use electricity more efficiently. Harvesting these "negawatts" may be the
fastest and cheapest way to cut carbon emissions. Amory Lovins and his Rocky Mountain
Institute have spent decades studying this approach.
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19 Aug, 2008
o
Posted by: Harry Read

I was very disapointed that algea farming was not mentioned under bio mass
anergy. Algea can produce 20000 gallons of suel oil per acre per year. One tenth the
state of New Mexico could provide all of the oil we need. No imported oil and the oil
supplied would be carbon neutrol. If you don't believe it look up algea farming on the
internet.
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21 Aug, 2008
o
Posted by: john clark

The capacity factor of solar cited is of course quite location sensitive, so it
inappropriate to quote a single capacity factor as you do when you write, "Of all
renewables, solar currently has the lowest capacity factor, at about 14%." As a counterexample, the capacity factor of the Stirling Energy Systems plant being built in Victorville,
CA for Southern California Edison is estimated as 23.9%. The company Ausra claims to
have a cost-effective Thermal Energy Storage for their Concentrated Solar Power system.
They claim in their whitepaper that they could power the U.S. 24x365. They write, "The
2005/6 U.S. national grid had a generating capacity of 1067 GW and non-coincident peak
load of 789 GW. Based on the current technology, a CLFR with SM3 and storage would
require 1.5 square miles for 177 MW, translating a national land requirement equal to
23,418 km^2 or a square with 153 km sides."
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29 Aug, 2008
o
Posted by: Earl Killian
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
"Algea", nothing. The energy problems of the world will be solved by a website I
went to that reduced my computer's electricity consumption to -2 kW. I know I wrote
down the URL somewhere. There was frost on the cooling air outlet. I think energy
carriers are important (http://www.eagle.ca/~gcowan/235_248.pdf ).
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30 Aug, 2008
o
Posted by: Graham Cowan

The biomass portion of this article neglects the large possibilities from
bioengineering of algae and plants to produce easily extracted liquid fuels and
biochemical products using tailored biosynthetic pathways. Current genetic engineering
techniques now make readily feasible the ideas put forth by Melvin Calvin over 40 years
ago. He was just a bit ahead of his time. For example one can readily imagine large
expanses of poor quality land being used to produce fuel from algae using sewage as a
source of nutrients and salt water as the water source. This would avoid the use of
farmland for biofuels with the concommitant effect on food prices we already see
happening.
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30 Aug, 2008
o
Posted by: Donald Condliffe

You appear to have neglected solar power satellites - perhaps not feasible
immediately, but the obstacles are engineering ones, not theoretical breakthroughs. One
of the above technologies (probably nuclear) could provide enough capacity until a
workable solar power satellite system could be developed. We don't have to limit
ourselves to the sunlight that hits the earth...
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02 Sep, 2008
o
Posted by: Alan Barker

A wellcome overview! Just to mention that a summary of this review has appeared
en français at http://www.sauvonsleclimat.typepad.fr/ It contains a couple of critical
comments on some of the proposed figures for the future.
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05 Sep, 2008
o
Posted by: Jean-Marc Bonneville

One thing is for sure. Liquid fuels, biofuels or otherwise, are going to become a
precious commodity worth their weight in gold. We need to prioritize finding ways to use
as little as possible. I'm skeptical we will find ways to produce liquid biofuels without
destroying carbon sinks and biodiversity or driving up the cost of food, especially in the
short term. And if we ever do, you can bet that producing them will be incredibly
expensive compared to simply pumping an energy dense liquid out of a hole in the
ground.
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