Forget hydrogen. Algae may be the fuel of the future.
A study by researchers at Pacific Northwest National Laboratory finds algal fuel could replace 17 percent of the petroleum the United States imports for transportation fuel each year.
Of course, one of the major concerns about algae is the volume of water needed to produce it. But the researchers note that water use can be significantly curtailed by raising algae in the humid climates of the Gulf Coast, Southeastern Seaboard and Great Lakes regions.
“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 hydrologist and lead author of the study, in a statement. “This research provides the groundwork and initial estimates needed to better inform renewable energy decisions.”
Algal fuels are made by extracting and refining the lipids within algae. Algae are attractive biofuel feedstock because it grows quickly and thrives in everything from seawater to irrigation runoff to sewage. Such fuels could go a long way toward meeting the Energy Independence and Security Act. That law requires that biofuels replace more than 10 percent of our current petroleum consumption by 2022. Half of that biofuel must come from something other than corn.
The PNNL study provides an in-depth assessment of the United States’ annual algal fuel potential given the available land and water.
The researchers, who detail their findings in Water Resources Research, analyzed currently available data to determine how much algae can be grown in open, outdoor ponds of fresh water — as is typical — using current tech.
First, they created a database analyzing topography, population, land use and other data about the contiguous United States. The info, spaced every 100 feet, allowed them to determine which areas are ideally suited to raising algae.
Then they gathered 30 years of weather info to determine how much sunlight the algae could realistically photosynthesize and how warm the ponds would become. They used that data in a mathematical model to calculate how much algae could be produced each hour at a given site.
Using that model, they say 21 billion gallons of algal oil could be produced domestically. That’s equivalent to 17 percent of the petroleum the United States imported for transportation fuel in 2008.
Growing all that algae would require land roughly the size of South Carolina and 350 gallons of water for each gallon of algal oil. All told, that comes to about 25 percent of the water we currently use for crop irrigation. (The researchers say that’s on par with ethanol.)
“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.”
If we went for broke and maxed out our capacity to produce algae, we could cut petroleum imports by 48 percent, the researchers say. But we’d need several times our annual consumption of irrigation water to do so. It isn’t terribly practical.
John Timmer, a biochemist who writes for our sister publication Ars Techica, offers some interesting analysis of the study.
He says the 48 percent figure is based on unrealistic assumptions. Even the possibility of replacing 17 percent of our oil imports with algal fuel must be taken with a grain of salt.
“Even for the more realistic scenarios, the list of caveats is pretty extensive,” he writes. “Water and nutrients are unlimited, only evaporation is considered, only open ponds are used, and the authors ignore the energy demand involved in keeping the ponds from freezing or processing the algae into fuel. ”
The authors identified areas that could be used for open ponds and focused on land that is relatively flat and isn’t farmland or parkland. That includes roughly 5 percent of the country’s land. If we used it all for biofuel production, we could produce 220 gigaliters a year, or about half our current oil imports, Timmer writes.
But we don’t have the water needed to do that.
With that in mind, Timmer writes, the researchers balance productivity and water requirements. That left the Gulf Coast, Southeast Seaboard and Great Lakes as ideal locations. And that led them to conclude we could replace 17 percent of our imported oil while consuming one-quarter of the water used each year for agriculture irrigation.
“That’s still quite high, but remember that this assumes unpolluted freshwater,” Timmer writes. “The areas along the Gulf and Atlantic cost could easily use a combination of saltwater and municipal waste. The latter source could potentially provide for facilities in some of the areas in the Southwest that are otherwise ruled out due to their high water use.”
Such details were beyond the scope of the PNNL study, but critical to consider, Timmer writes. The authors hope other researchers use their model to conduct further studies.
“Ideally, if they’re taken up on this offer,” Timmer writes, “we’ll have a clearer picture of the potential of algal biofuels.”
Photo: Raceway alge ponds in Southern California. /Pacific Northwest National Laboratory.
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