NREL Researcher Kim Christensen analyzes an algae sample for oil content.
From NREL and Chevron: A Super Fuel
December 2008 / January 2009
Volume 6 Number 6
Put some algae in a shallow pond of water unfit for agricultural uses, stir in some simple nutrients and an exhaust gas that's threatening the Earth's climate and let it all cook in the sun for a few days. That's the National Renewable Energy Laboratory's recipe for a new sustainable fuel resource. If the recipe works, you can harvest a bumper crop of microscopic algae, or "microalgae," extract its oil and ship the oil to a petroleum refinery, which can turn it into renewable-source "green" diesel, jet fuel or even gasoline. The production of oil from microalgae could also be dramatically higher per acre than it is for soybeans and other oil seed crops—€”perhaps as much as 20 times higher.
Many species of microalgae naturally produce up to 20 percent of their body weight as lipids, fats or oils that can be converted to fuel. When these micro algae are starved of the nutrients they need, their lipid content can increase as much as 60 percent.
To make good use of this extraordinary oil-producing capability, NREL and Chevron Corporation signed a Department of Energy cooperative research and development agreement (CRADA) in October 2007. Under the agreement, NREL will develop ways to increase the productivity of these microalgae. Chevron anticipates using the resulting oil as a feedstock for renewable transportation fuels.
Microalgae oil production has everything going for it in terms of being an environmentally ideal recipe for biomass energy. For example, microalgae can be grown on land that's not suitable for conventional crops and in salty water that's unfit for conventional agricultural or domestic uses.
Growing microalgae could also be one of the most effective ways of reducing carbon dioxide emissions. Algae, like terrestrial plants, take up carbon dioxide directly from the atmosphere as they convert light energy into chemical energy by means of photosynthesis. But algae can be stimulated to grow more vigorously by being "fed" with carbon-dioxide-rich air streams from power plant flue gases or other sources.
From 1978 to 1996, the laboratory was a pioneer in the field with the Aquatic Species Program. In it, researchers screened and characterized more than 3,000 potential strains, shed light on the growth conditions that stimulate lipid production, demonstrated open ponds for mass production of biomass and made significant breakthroughs in genetic engineering. When the program ended, the technology was considered to be highly promising but not yet cost competitive with petroleum-based fuels.
Today, however, it's time to take the microalgae-fuel recipe off the back burner. While petroleum prices are up, new petroleum refinery processes are better able to handle algae-derived oils. Algae farming techniques have also changed. NREL used to grow algae in large, shallow outdoor ponds. Today, microalgae are grown within inexpensive plastic tubes or similar enclosed bioreactors. In fact, more than 50 companies have sprung up over the last several years to research microalgal oil production, focusing primarily on developing novel bioreactors while using existing algal strains. The most exciting change for NREL's researchers, however, is that the science has improved.
"In the —€˜80s and —€˜90s, efforts to increase oil production in algae were largely based on the Edisonian approach: —€˜try something and observe what happens.' Now, new biotechnologies give us far greater capability to understand how an organism responds to various environmental factors that influence growth," says Al Darzins, who is directing the Chevron CRADA work.
"The new excitement about microalgal oil has lots of people looking at engineering better bioreactor systems, but not as many at the underlying biology of the organisms, and that is crucial," says Darzins.
Howard Brown is a senior communicator at NREL.
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