A few years back when I first joined Bobby's group here I wrote that I was
skeptical of the growth directions I received for Arthrospira Platensis
("spirulina") from Carolina Scientific which said:

"Blue-green algae have a tendency to bleach easily under high light
intensities. For this reason, we place our initial subcultures in an
area where they get only about 100 footcandles of light. Certain algae
such as Spirulina and Arthrospira never do well under direct light and
should be kept at very low light intensities at all times."

http://tech.groups.yahoo.com/group/oil_from_algae/message/246

During the experiments with A.S. (which I logged here) I convinced myself that
the claim was correct but also came to understand how raceway ponds in full
desert illumination worked: They exposed individual cells to full illumination
for only a fraction of the time -- during which the cells charged up their ATP
stores -- and submerged them to shield against bleaching while the cells
continued the photosynthesis process using up their ATP stores. The raceway
cells are exposed to PEAK light levels FAR in excess of what they can tolerate
as AVERAGE light levels!

This makes evolutionary sense -- just as do many other aspects of algae once you
get to know them. For another instance, the alkalinity of water in which algae
can thrive "coincidentally" scrubs air of its CO2 which, again, "coincidentally"
is just what the algae need to thrive. No -- this is no "coincidence", it is
what Richard Dawkins described as a fundamental aspect of ecological evolution
which he calles "the extended phenotype": altering the environment to be
suitable for the replication of the genes.

OK, so I understood why the Earth Rise Farms guys weren't idiots with their
raceway ponds. So I started thinking about the next problem, which is how to
lower the price per insolated algae pond to the point that the biodiesel output
could amortize the capital costs. Here I ran into a brick wall, because you
_have_ to cover the algae -- not so much because you have to keep the strains
free from contamination (Earthrise sells nutraceutical purity spirulina grown in
open ponds) -- but because you have to keep the temperature of the growth medium
high enough for the dark phase of photosynthesis (ATP metabolism) to proceed at
a high rate. My calculations showing the economic infeasibility of algae
biodiesel in covered raceway ponds were posted here:

http://tech.groups.yahoo.com/group/oil_from_algae/message/1557

At that time I decided the best course of action was to simply focus on the
production of EPA from Nannochlorposis and feed the remainder of the biomass to
algae grazing fish. Still think this is likely to be the best INITIAL route to
making algae ponds profitable. I saw the potential for a "biosphere home":

http://tech.groups.yahoo.com/group/oil_from_algae/message/1856

and even a circular "biosphere city" of 200,000 people based on a solar updraft
tower design which I posted here in a series with various corrections:

http://tech.groups.yahoo.com/group/oil_from_algae/message/1811

and which is consolidated into a single proposal proforma at my site:

http://www.geocities.com/jim_bowery/sutabs.html

I believe these to be the best current proposals (other than mariculture) for
realizing algae's tremendous potential to provide biomass from atmospheric CO2
and I eagerly await someone to provide better proposals. I've been waiting
years...

Well, there may be another approach to photobioreactors, depending on the peak
rate at which a single algae cell can convert light into ATP:

Rather than trying to disperse solar energy into the growth medium to achieve
the optimal AVERAGE illumination -- a strategy that raises the capital costs
above that which can be supported by any market other than, perhaps, EPA/DHA
nutraceuticals -- try, instead, to reduce the cost of to approach that of solar
mirrors which concentrate sun to expose high-flow-rate algae streams, similar to
the solar heating collectors:

http://www.dlr.de/en/Portaldata/1/Resources/portal_news/newsarchiv2007/Sopran_Os\
t.jpg

Obtaining the actual parameters of ATP creation would be necessary to reengineer
solar heating mirror systems to grow algae, but it seems that if
mirror-collected solar heat is a reasonable proposition to begin with, adding
algae biomass to its value stream should be feasible.

I understand that there have been proposals to do something like trough
collectors for algae biodiesel growth, but these generally are not trying to
minimize the capital cost of insolated area and they frequently resort to exotic
technologies like conversion of the unused portion of the spectrum to
electricity to then be used to further illuminate the algae. I am _very_
skeptical of the economics of this approach. Rather, I see the existing
application of solar heating as a sound basis for further extension -- keeping
the capital cost per insolated area minimized.