Biomass more efficient if turned into electricity, study says

Using biomass to produce electricity is 80 percent more efficient than transforming the biomass into biofuel. In addition, the electricity option would be twice as effective at reducing greenhouse-gas emissions.

The results are from a study done by a collaboration between researchers at Stanford University, the Carnegie Institute of Science, and the University of California, Merced and published on the latest Science issue and imply that investment in an ethanol infrastructure, even if based on more efficient cellulosic processes, may prove misguided.

The researching team concludes, also, there is a potential of capturing and storing the carbon dioxide emissions from power plants that use switchgrass, wood chips, and other biomass materials as fuel – an option that doesn’t exist for burning ethanol.

When burned, biomass releases CO2 in the air. Overall, though, carbon dioxide production is lesser than with fossil fuels because plants grown to replenish the resource are assumed to reabsorb those emissions. Capturing those combustion emissions to sequester them underground would “result in a carbon-negative energy source that removes CO2 from the atmosphere,” according to the study.

Findings are based on scenarios developed under the Biofuel Analysis Meta-Model (EBAMM) created at the University of California, Berkeley. The analysis covered a range of harvested crops, including corn and switchgrass, and a number of different energy-conversion technologies. Data collected were applied to electric and combustion-engine versions of four vehicle types–small car, midsize car, small SUV, and large SUV–and their operating efficiencies during city and highway driving.

The study targeted the amount of energy required to convert biomasses into ethanol and electricity, as well as the energy intensiveness of manufacturing and disposing. results show bioelectricity far outperformed ethanol under most scenarios, although the two did achieve similar distances when the electric vehicles – specifically the small car and large SUV – weren’t designed for efficient highway driving.

The potential is even greater for the bioelectricity option because under the EBAMM model, “we did not account for heat as a [usable] by-product, which would make the electricity pathway even more advantageous,” says Elliott Campbell, lead author on the study and an assistant professor at the Sierra Nevada Research Institute, part of the University of California, Merced.

A similar but much broader study released in December by Mark Jacobson, a professor of civil and environmental engineering at Stanford University, focused more on the environmental effects of various energy options. Though he doesn’t support using biomass for either electricity generation or ethanol production, Mark Jacobson recognizes he isn’t surprised to find that the ethanol option performed worst for burning biomass, “is not necessarily an efficient way of generating electricity, but it’s more efficient than making biofuel.” It just makes sense, he adds: “Electric vehicles are four to five times more efficient than combustion vehicles.”

Montreal-based cellulosic ethanol producer Enerkem’s president, Vincent Chornet, says that it would be a mistake to pick winners: there’s room for both options, depending on local conditions of infrastructures.


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