Thursday, May 22, 2008

Some comments on Algae yields

For anyone involved in the recent hype about Algae cultivation for Biofuels it is very difficult to get a grip on what production values you should believe and more over how you should compare apples and apples. In this blog I try to analyse the actual potential and the differences between an Open Pond system and a Photo Bioreactor.

I have used the information available on the web from Dr. Gedaliah Shelef who made some interesting research of Open Pond systems back in the late 70's maybe in the 80's, no date mentioned. Now remember that 1978 is 30 years ago and I was just starting secondary first, so some progress must have been made, I guess.

The second information is the information available from AlgaeLink, I have used the example of their 10 ton production plant for comparison, however the numbers are the same for all their production equipment.

Now when comparing the two systems there is one very important factor to keep in mind, Open Pond systems normally calculate yield in gram Algae per square meter per day (g/m2/day). The norm for Photo Bioreactors are to use gram Algae per cubic meter per day (g/m3/day). Now this is causing a lot of confusion and I guess that one way of sorting this out is to measure the yields in ton per area.

This make sense, since in the end the critical factor will be the area available for cultivation, not the volume. This is at least true for current solutions, both open pond and Photo Bioreactor, and until there is a solution for growing vertically the area used will be the biggest limitation.

Now when we are talking about yield per area there is also confusion between Hectares (1 Ha = 10.000 m2) and Acres (1 Acre = 4. 047m2). So to try to make some sense to the story, here is a summary:

You may want to download your own copy to play with here.

Now let us analyse this for a moment. To explain the columns the two first ones are based upon the Open pond system with the first column has the actual numbers and the second one a "guesstimation" about potential yield 30 years down the road (increase from 28 to 50 g/m2/day).

The three last columns are based upon AlgaeLink numbers, the first one has a yield of 1.500 g/m3/day as stated in their website, however this seems to me like rather wishful theory and hence I have reduced the two following columns to more realistic 600 g/m3/day and 300 g/m3/day.

What we get out of this analysis is that the Open Pond yield is somewhere between 35-60 ton/ha/year and that a Photo Bioreactor has a yield of 75-365 ton/ha/yr. This would indicate that the Photo Bioreactor is between 2-6 times as more effective, probably somewhere in between, lets say something like 3 times more effective.

So let us put this in perspective.

If we can achieve the theoretical targets of 15.000 gallons/acre/yr of BioDiesel from Algae (note I am using US units here to make it easier) in a Photo Bioreactor, we should be able to get out 5.000 gallons/acre/year from an Open Pond system, compare this to Palm Oil, 600 gal/ac/yr and Jatropha 60 gal/acr/yr.

This has some rather interesting implications for the future applications of Open Pond and Photo Bioreactors and the different potential application areas and market segments, however more about that some other time....

Stay tuned.


Dr. Gedaliah Shelef, article here.
AlgaeLink, technical specification here.

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