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Algae Biodiesel

Although algae biodiesel production is not commercial yet, it is a promising field. As you already know, biofuels are solar energy captured by plants and converted into chemical energy through photosynthesis. This stored energy takes the form of oils, carbohydrates, proteins, etc. Algaes are among the most photosynthetically efficient plants. Some species reach over 50% w/w oil and have high growth rates. It has been estimated that algae farms in the future could completely replace petroleum as a transportation fuel in the US.

The Office of Fuels Development, a division of the Department of Energy, funded a program under the National Renewable Energy Laboratory (NREL) known as the "Aquatic Species Program". The focus of this program was originally to use fast-growing algae to sequester carbon in CO₂ emissions from coal power plants. Then, because of the high content of oil of some species of algae, the focus of the project shifted to wide scale biodiesel production.

Although, there are several technological problems yet to be solved, algae biodiesel has great potential. For example, algae farms could use waste streams from animal farms as a food source. Besides oil for biodiesel, nutrients can also be extracted from algae for the production of a fertilizer high in nitrogen and phosphorous. This makes a full cycle that provides a safe and clean method of fertilizing than spreading manure or wastewater treatment plant bio-solids on farmland.

The following is an excerpt from UNH Biodiesel Group researcher Michael Briggs in “The Answer is Biodiesel”. The UNH Biodiesel Group is working on improving the technology for growing algae on waste streams for biodiesel production. UNH has filed a provisional patent application and is seeking partners to develop the technology.

For more information contact Michael Briggs at msbriggs@cisunix.unh.edu.

NREL's research showed that one quad (ten billion gallons) of biodiesel could be produced from 200,000 hectares of desert land (200,000 hectares is equivalent to 780 square miles, roughly 500,000 acres), if the remaining challenges are solved (as they will be, with several research groups and companies working towards it, including ours at UNH).

We have found that to replace all transportation fuels in the US, we would need 140.8 billion gallons of biodiesel, or roughly 19 quads (one quad is roughly 7.5 billion gallons of biodiesel). To produce that amount would require a land mass of almost 15,000 square miles. To put that in perspective, consider that the Sonora desert in the southwestern US comprises 120,000 square miles.

Enough biodiesel to replace all petroleum transportation fuels could be grown in 15,000 square miles, or roughly nine percent of the area of the Sonora desert. (Note for clarification — I am not advocating putting 15,000 square miles of algae ponds in the Sonora desert. This hypothetical example is used strictly for the purpose of showing the scale of land required.) That 15,000 square miles works out to roughly 9.5 million acres — far less than the 450 million acres currently used for crop farming in the US, and the over 500 million acres used as grazing land for farm animals.

These projected yields of course depend on a variety of factors, sunlight levels in particular. The yield in North Dakota, for example, wouldn't be as good as the yield in California. Spreading the algae production around the country would result in more land being required than the projected 9.5 million acres, but the benefits from distributed production would outweigh the larger land requirement.

In "The Controlled Eutrophication process: Using Microalgae for CO2 Utilization and Agircultural Fertilizer Recycling", the authors estimated a cost per hectare of $40,000 for algal ponds. In their model, the algal ponds would be built around the SaltonSea (in the Sonora desert) feeding off of the agircultural waste streams that normally pollute the Salton Sea with over 10,000 tons of nitrogen and phosphate fertilizers each year.

The estimate is based on fairly large ponds, 8 hectares in size each. To be conservative (since their estimate is fairly optimistic), we'll arbitrarily increase the cost per hectare by 100% as a margin of safety. That brings the cost per hectare to $80,000. Ponds equivalent to their design could be built around the country, using wastewater streams (human, animal, and agricultural) as feed sources. We found that at NREL's yield rates, 15,000 square miles (3.85 million hectares) of algae ponds would be needed to replace all petroleum transportation fuels with biodiesel. At the cost of $80,000 per hectare, that would work out to roughly $308 billion to build the farms.

The operating costs (including power consumption, labor, chemicals, and fixed capital costs) taxes, maintenance, insurance, depreciation, and return on investment worked out to $12,000 per hectare. That would equate to $46.2 billion per year for all the algae farms, to yield all the oil feedstock necessary for the entire country. Compare that to the $100-150 billion the US spends each year just on purchasing crude oil from foreign countries, with all of that money leaving the US economy.

These costs are based on the design used by NREL — the simple open-top raceway pond. Various approaches being examined by the research groups focusing on algae biodiesel range from being the same general system, to far more complicated systems.

As a result, this cost analysis is very much just a general approximation. Some systems could be considerably more expensive, but could also see considerably higher yields, resulting in less land being required. How exactly the economics play out will hopefully be decided over the next few years as some of these groups research algal biodiesel bring their systems to commercialization status.

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