Biodiesel From Algae - A Techies Viewpoint

Source: The Oil Drum
Date: May 11, 2007

During the oil crisis of the 1970s, Congress funded the National Renewable Energy Laboratory (NREL) within the Department of Energy to investigate alternative fuels and energy sources. The Aquatic Species Program (ASP) focused on the production of biodiesel from high lipid-content algae growing in outdoor ponds. These programs also used carbon-dioxide from coal fired plants to increase the growth rate and lipid content of algae. They estimated that under optimum growing conditions micro-algae will produce up to 4 lbs./sq. ft./year or 15,000 gallons of oil/acre/year. Micro-algae are the fastest growing photosynthesizing organisms. They can complete an entire growing cycle every few days. Based on this one can extrapolate that it would take about 10 million acres to produce 145 billion gallons of biodiesel which could supply the entire US gasoline requirements (assuming gasoline powered vehicles could be replaced over time). That is just 2.3% of total area used to grow crops in the US! So why isn't someone doing something constructive in this field?

There are at least 4 different ventures in the works, including Aquaflow Bionomic, Solio Biofuels, GS Cleantech, and GreenFuel Technologies. GreenFuel seems to be the most advanced in mass commercialization of this technology. GreenFuel Technologies along with De Beers in South Africa (no relationship to the diamond miner) have been making some rather audacious claims on this front. As mentioned here they plan to single handedly make peakists shake in their boots. Greenfield/De Beers plan to produce about 391,000 barrels per day in 5 years. That is no chump change. There are just a couple of major oil fields coming online within the next 5 years which produce anywhere close to that. So Should Chris Skrewbowski start including De Beers in his mega projects list? Not so fast.

According to GreenFuel's patent application a 1.3 sq. km. plant can generate 342,000 barrels of biodiesel per year. Now, I am not very familiar with km-acre relationship so I had to look it up. I got my wife to double check my numbers as I kept believing I screwed up somewhere. GreenFuel claims to be able to produce 45,000 gallons/ acre/ year. I have converted these to an easy to compare number to that of APS above. So GreenFuel is thus claiming to do 3 fold as well as, the highest estimate under super-optimistic conditions that has never been produced on a large scale. Also, ASP had dismissed closed photo bioreactors has prohibitively expensive but it was not clear what price of oil they were taking into their equation.

This last alliance of GreenFuel and De Beers which is making it's stand against the dark forces of peak oil is even convincing the common public that it can do this. De Beer's has sold shares to the common public (without a prospectus) and 29 franchises to build 91 plants (for 6 Million Rand each). Additionally they guarantee that each plant will produce more than 850 barrels of biodiesel per day.

Let's examine their claims in light of (pun intended) how much lipid photosynthetic organisms can synthesize.

Photosynthetic organisms (PO), such as algae, transform visible light in the 400-700 nm part of the spectrum - called photosynthetically active radiation (PAR) - into the chemical energy of carbon-containing compounds. PAR varies with latitude, seasonality and geographical factors. PAR in the southwest US is about 105w/sThe energy - in the form of biomass - that can be obtained via photosynthesis thus depends on the level of PAR and the efficiency of the conversion process Q.

Ebiomass = PAR x Q

Photosynthetic organisms use eight photons to capture one molecule of CO2 into carbohydrate (CH2O)n Given that one mole of CH2O has a heating value of 468kJ and that the mean energy of a mole of PAR photons is 217.4kJ, then the maximum theoretical conversion efficiency of PAR energy into carbohydrates is:

468kJ/(8 x 217.4kJ) = 27%

This is the ideal yield on PAR energy that is: (i) actually absorbed by the photosynthetic organism, (ii) in conditions where this organism operates with 100% photosynthetic efficiency (every photon that is absorbed is effectively used in photosynthetic reactions), and (iii) the organism does not waste any energy on any life-support functions, other than building biomass. We will call this efficiency Qtheo.

If 27% is theoretical maximum, then what is most likely? Dr. Dimitrov presents reasonable evidence to suggest that Q is likely to be around 10% at best. While that to some may sound like he is being overly pessimistic, it is my belief that he is in fact being a bit optimistic.
 
Here are his assumptions, 90% photosynthetic efficiency i.e how well an organism avoids photosaturation ...Q= 24.3 80% conversion of this amount for us..i.e the plant uses 28% energy for its own needs...Q=19.44 70% optical efficiency of the process, which measures optical coefficient, cleanliness and reflection of light from reactor wall..Q=13.60 98% efficiency in coverting biomass to biodiesel.. Q=13.33 98% plant efficiency (2% down time) Q=13.06

I have studied these in depth and I believe that getting anything over 15% is going to be an impossible task in the near future. A more likely situation is that Q will be around 10. Applying this to PAR of 105w/s/ sq.m or 3.3GJ/yr/sq.m. we get a maximum biofuel energy content of 0.89GJ/yr. Now, biodiesel has an  energy content of 0.133GJ/gallon. Greenfuel says that they plan on getting 342,000bbl per year from a 1.3 sq km plant. That is an energy content of 1.47 GJ/sq.m/yr.)