On Mar 22, 5:06 am, David Walker <d.a.wal... from sheffield.ac.uk> wrote:
> "Algae yields have not yet been accurately determined, but DOE is
> reported as saying that algae yield 30 times more energy per acre than
> land crops such as soybeans, and some estimate even higher yields up to
> 15000 gpa"
>> I read statements such as the above with increasing scepticism. Does
> anyone have verifiable figures (in tons per acre per year) of biomass
> for algae such as Chlorella or Spirulina ?
Other people have questioned this number (reference 1) and thought is
was incorrect. The origin seems to be from a 1998 DOE report
summarizing research on biodiesel from algae from 1978 to 1996
(reference 2). The report noted
"microalgae are capable of producing 30 times the amount of oil per
unit area of land, compared to terrestrial oilseed crops"
but provided no reference for that claim.
Under open pond conditions, DOE research found a maximum daily yield
of 50 g dry matter per square meter per day but long term productivity
of only 10. They also noted that low temperatures in the New Mexico
desert greatly limited algae productivity in open ponds.
The research in the Executive Summary of the DOE report is
surprisingly preliminary. They grew algae and measured productivity
but there was no mention of an actual pilot algae biodiesel project to
determine just how much biodiesel could be produced per hectare per
year outdoors in the open ponds.
It also appears that the enticing figure of 60% oil content for some
algae species only occurs under silicon-deficient or nitrogen-
deficient conditions, so is misleading. Mineral nutrient deficiencies
would lower the overall oil production of the algae.
The statement you quoted is contradictory because if algae yields have
not been "accurately determined" it could not be known that algae
yields are 30 times better than soybean. It is likely that the DOE
used rose-colored glasses to get the most optimistic prediction
possible. To do this one could take the highest daily algae yield
(i.e. 50 g per square meter per day) and extrapolate to long term
field conditions. To make as big a difference as possible one could
compare an average soybean yield with one crop per year to continuous
algae culture under optimal conditions. The productivity difference
between the two is magnified greatly because the soybean field is
fallow more than half the year. They may have also have used the
misleading 60% oil content figure for algae. Soybean is only about 15
to 20% oil and that for just the seed, not the entire organism as in
There is a lot of hype associated with biofuels. The Bush
Administration has so politicized U.S. government science agencies
that one can no longer believe everything that they report. The U.S.
corn ethanol program is clearly a boondoggle. Dr. Tad Patzek of the
University of California, Berkeley and Professor David Pimentel of
Cornell have carefully analyzed the energy cost of converting corn
grain to ethanol. Pimentel concluded "It takes more [fossil fuel]
energy to make ethanol from grain than the combustion of ethanol
produces." (reference 3).
David R. Hershey
1. 2004. Algae as a biomass source.
2. 1998. A Look Back at the U.S. Department of Energy's Aquatic
Species Program: Biodiesel from Algae.
3. 2001. Ethanol fuel from corn faulted as 'unsustainable subsidized
food burning' in analysis by Cornell scientist.