Archive for February, 2010

Algae Energy Analysis, or You Do The Math: The Clarens Paper
February 8, 2010

Instead of getting into algae economics right away, I am in this post responding to a current event of interest…

The algae cycle? from

The headline sure looks bad: “Engineers Find Significant Environmental Impacts With Algae-Based Biofuel.”  The New York Times, U.S. News and World Report, and Science Daily all join the hue and cry:

“The U.Va. research, just published in the journal Environmental Science & Technology, demonstrates that algae production consumes more energy, has higher greenhouse gas emissions and uses more water than other biofuel sources, such as switchgrass, canola and corn.”

Algae has been sold on its green-ness, so this is a stab at the very heart of the nascent industry.  The Algae Biofuel Association fired back the next day, pointing out that much of the data used by the study was from the 70’s and 80’s, and that newer algaculture techniques invalidate the numbers they used.
Now, I have no doubt that new technology will improve algae biofuel’s carbon footprint.  But having read the paper and the online supporting materials, I don’t think that simply invoking the promise of new technology really gets at what the paper was about.

I’d like to do that here.

Part 1:
Is a pile of sticks really the same as a tank of gas?

The authors open their paper with a premise that wipes many of algae’s advantages off the map at the outset.  They declare that they will compare algae to corn ethanol, soy biodiesel, and switchgrass ethanol on a purely energy basis, including the stalks and leaves as equal in value to the starch and oil portions that are currently used for fuel.  Now, plants make their structure out of materials evolutionarily designed to be resistant to breakdown — cellulose, hemicellulose, and lignin — and so making it into fuel requires highly specialized, finicky organisms, or high temperatures to decompose these tough compounds.  All this requires a lot of infrastructure, and a lot of energy (which is why it takes about as much energy as is in corn ethanol to make it), as does gathering up and chopping up plant materials until they are digestible chunks sitting in a bin in a biorefinery.

Algae are a very different picture, and this is one of the main reasons for all the interest in them.   Their biomass can be over 50% vegetable oil (compared to 2-3% for typical conventional oil crops), which can be pumped and pipelined to a standard refinery and transformed with conventional, low-energy methods into gasoline, diesel, and jet-fuel equivalents.    Uncle Joe can also make it into biodiesel in his garage with minimal inputs or even know-how. Try doing that with a pile of damp switchgrass.

But this is a minor objection compared to what the authors did next.

Part 2:
These algae are made for recycling, and that’s just what they’ll do

From the headline, one might assume that the excessive energy use claimed arises from the operations of the algae farm — paddlewheels, centrifuges, and such — after all, it seems like a higher-tech form of farming, involving more gear — but a quick glance at the energy breakdown shows that something altogether different is going on.  In fact, over 97% of the claimed water use and 94% of the energy use arises from the manufacture of fertilizer, CO2, and other chemicals.  Now the technology for synthetic fertilizer (the Haber-Bosch process) was originally developed for explosives, so it should come as no surprise that their manufacture consumes a lot of energy.  That the authors take this into account is valid in theory, but they make an assumption that runs against the most basic economic considerations of algae farming — that the farmers, after extracting the lipid fraction of their algal harvest, will inexplicably burn the remaining fraction for the meager heating value retained therein, then throw the nutrient-rich ash into a landfill.  Assuming that the algae farmer has even a lick of sense, she’ll put those nutrients back into the pond.  The ability to recycle nutrients almost completely is one of the great advantages of algae farming over traditional farming.

Nutrient recycling, plus the use of exhaust for CO2 (which every biofuel algae farmer I’ve ever met intends to do), profoundly changes the analysis, and in fact reverses the result that was trumpeted across all the headlines.  With 100% nutrient recycle, using the authors’ numbers, algae biofuels come out well ahead of corn, canola, and switchgrass, even using the authors’ approach of equating haybales and barrels.  With 95% nutrient recycle, algae still comes out on top of all comers except a slight loss to switchgrass on water use.  This is comparing apples to oranges, though, as switchgrass requires scarce fresh water, and algae can grow in salt- and waste-water.

Part 3:
The Land will have the last word.

The authors chose to ignore the greenhouse gas impacts of indirect land-use changes, which can be a hundred times greater than the annual emissions thought to be saved by land crop-based biofuels, and really, IMO, should rule out any land crop-based biofuel not grown on truly marginal land.  Algae do not use arable land, and so avoid this impact as well as competition with food production.


So a little digging reveals that the media’s presentation of the results of this paper are entirely misleading.  I do agree with the authors regarding the advantages of the use of wastewater (the NASA project I’m working on is designed to use wastewaster for nutrients and exhaust for CO2), and as far as source-separated urine as an algae nutrient source goes, this has been a favorite research area of mine (bottom line: it works great!), so we don’t disagree about everything.

But it’s hard to overlook the fact that a result so contrary to the algae industry’s founding notions is music to the ears of some in the ethanol crowd, who are beginning to feel some competition from algae for the title of “fuel of the future”.

P.S. If you wonder about my qualifications to evaluate the quality of another scientist’s energy analysis, please take a look at my recent paper comparing energy use in organic farming to that of conventional methods, (here’s a link to a pdf of my slides) in unprecedented detail (which turns out to be pretty important).  I have also written a consulting report on biofuel energy balances, so I feel qualified to say that these guys are way off the mark, for reasons much more fundamental than those cited by the ABO.

But I encourage you all to look at the paper itself, and to give comments and feedback.  Thanks!