Oil produced by algae growing in an area roughly the size of South Carolina could replace a sizable chunk of the oil the United States imports for transportation, according to a new analysis that also contends that water use — a drawback to algal biofuel — could be minimized.
"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," said Mark Wigmosta, a U.S. Department of Energy hydrologist who was the lead researcher for the analysis. "This research provides the groundwork and initial estimates needed to better inform renewable energy decisions."
The researchers concluded that farmed algae could produce 21 billion gallons of oil, fulfilling a federal goal set for advanced biofuel production in 2022. Growing algae domestically would help reduce the U.S. dependence on foreign oil — in 2009, slightly more than half of the petroleum used in the U.S. came from abroad.
Algae grown in freshwater ponds in the country's most sunny and humid climates — the Gulf Coast, the southeastern seaboard and the Great Lakes — would require the least water, the researchers said.
Algae have some important advantages as a source of biofuel, which in this case would be made by extracting and refining oils called lipids produced by the simple plants. Algae can produce 80 times more oil than an equal area of corn does. And unlike with corn, which is used to make ethanol, algae grown for biofuel production wouldn't interfere with a food crop, since algae aren't a widespread food source. Algae also consume carbon dioxide, the primary greenhouse gas, and can grow in (and clean) municipal wastewater.
But algae, like other biofuels, require a lot of water to produce. This is not an issue with conventional petroleum, which is extracted from the Earth, not grown. [The Real Costs of Renewable Energy]
Wigmosta, who works at the DOE's Pacific Northwest National Laboratory, and his colleagues set out to assess just how much algae-derived oil the United States could produce and how much water that would require. Using geographic data, they identified areas suited for growing algae in freshwater ponds. Using weather data to estimate amount of sunlight (since algae rely on photosynthesis to grow) and temperature, the researchers calculated the amount of algae that could be produced hourly at each specific site.
They also estimated how much water would need to be replaced due to evaporation over 30 years, based on growing algae in open, outdoor, freshwater ponds using current technology.
They calculated that enough algae to produce 21 billion gallons of oil — 17 percent of the petroleum that the U.S. imported in 2008 for transportation fuels — could be grown on lands roughly totaling the size of South Carolina, using 350 gallons of water per gallon of oil produced. This amounts to a quarter of the water currently used for agriculture.
"Water is an important consideration when choosing a biofuel source," Wigmosta said. "And so are many other factors. Algae could be part of the solution to the nation's energy puzzle if we're smart about where we place growth ponds, and the technical challenges to achieving commercial-scale algal biofuel production are met."
The analysis appears in the journal Water Resources Research.