A new Pacific Northwest National Laboratory (PNNL) study shows finds that oil from algae grown in outdoor raceway ponds located in the Gulf Coast, the Southeastern Seaboard and the Great Lakes could replace 17% of the United States’ imported oil for transportation.
The study also found that shows that water use for algae cultivation is much less if algae are grown in the US regions that have the sunniest and most humid climates: the Gulf Coast, the Southeastern Seaboard and the Great Lakes. The paper is published in the journal Water Resources Research.
Algae has been a hot topic of biofuel discussions recently, but no one has taken such a detailed look at how much America could make—and how much water and land it would require—until now. This research provides the groundwork and initial estimates needed to better inform renewable energy decisions.—Mark Wigmosta, lead author and a PNNL hydrologist
Wigmosta and his co-authors provide the first in-depth assessment of America’s algal biofuel potential given available land and water. The study also estimated how much water would need to be replaced due to evaporation over 30 years. The team analyzed previously published data to determine how much algae can be grown in open, outdoor ponds of fresh water while using current technologies. Although algae can also be grown in salt water and covered ponds, the authors focused on open, freshwater ponds as a benchmark for this study; much of today's commercial algae production is done in open ponds.
First, the team developed a comprehensive national geographic information system database that evaluated topography, population, land use and other information about the contiguous United States. That database contained information spaced every 100 feet throughout the US—a much more detailed view than previous research. This data allowed them to identify available areas that are better suited for algae growth, such as those with flat land that isn’t used for farming and isn’t near cities or environmentally sensitive areas like wetlands or national parks.
Next, the researchers gathered 30 years of meteorological information. That helped them determine the amount of sunlight that algae could realistically photosynthesize and how warm the ponds would become. Combined with a mathematical model on how much typical algae could grow under those specific conditions, the weather data allowed Wigmosta and team to calculate the amount of algae that could realistically be produced hourly at each specific site.
The researchers found that 21 billion gallons of algal oil, equal to the 2022 advanced biofuels goal set out by the Energy Independence and Security Act, can be produced with American-grown algae. That’s 17% of the petroleum that the U.S. imported in 2008 for transportation fuels, and it could be grown on land roughly the size of South Carolina. But the authors also found that 350 gallons of water per gallon of oil—or a quarter of what the country currently uses for irrigated agriculture—would be needed.
The study also showed that up to 48% of the current transportation oil imports could be replaced with algae, though that higher production level would require significantly more water and land. So the authors focused their research on the US regions that would use less water to grow algae, those with the nation’s sunniest and most humid climates.
The authors also found that algae’s water use isn’t that different from most other biofuel sources. While considering the gas efficiency of a standard light-utility vehicle, they estimated growing algae uses anywhere between 8.6 and 50.2 gallons of water per mile driven on algal biofuel. In comparison, data from previously published research indicated that corn ethanol can be made with less water, but showed a larger usage range: between 0.6 and 61.9 gallons of water per mile driven. Several factors—including the differing water needs of specific growing regions and the different assumptions and methods used by various researchers—cause the estimates to range greatly, they found.
Because conventional petroleum gas doesn’t need to be grown like algae or corn, it doesn’t need as much water. Previously published data indicated conventional gas uses between about 0.09 and 0.3 gallons of water per mile.
Looking beyond freshwater, the authors noted algae has several advantages over other biofuel sources. For example, algae can produce more than 80 times more oil than corn per hectare a year. And unlike corn and soybeans, algae aren’t a widespread food source that many people depend on for nutrition. As carbon dioxide-consuming organisms, algae are considered a carbon-neutral energy source. Algae can feed off carbon emissions from power plants, delaying the emissions’ entry into the atmosphere. Algae also digest nitrogen and phosphorous, which are common water pollutants. That means algae can also grow in—and clean— municipal waste water.
Next up for Wigmosta and his colleagues is to examine non-freshwater sources like salt water and waste water. They are also researching greenhouse ponds for use in colder climates, as well as economic considerations for algal biofuel production.
The research was funded by DOE’s Office of Energy Efficiency and Renewable Energy.
Mark S. Wigmosta, Andre M. Coleman, Richard J. Skaggs, Michael H. Huesemann, Leonard J. Lane (2011) National Microalgae Biofuel Production Potential and Resource Demand. Water Resources Research. doi: 10.1029/2010WR009966