Energy from Biomass

How much energy can we really expect from miscanthus, switchgrass, and other types of biomass?

Energy produced from biological matter (biomass) currently provides about 10 percent of the world’s energy demands. Most experts predict that the contribution of bioenergy will only grow in the coming years, but there remains considerable debate about how much much energy we can really expect from corn, miscanthus, switchgrass, trees and other biomass sources. Some foresee explosive growth in biofuel production, while others see modest, even incremental gains.

A report from the UK Energy Research Center – Energy from Biomass: The Size of the Global Reserve -- attempted to clarify the picture through a systematic review of recent studies. Like the U.S.  Department of Energy’s “Billion Ton Update” on biomass availability, the report uncovered widely different assumptions about the basics of biofuel production, -- including the availability of land, competition for land and the productivity of food and fuel crops. Until researchers can settle on these basic concepts, disagreements about the future of bioenergy will rage on.

At the low end of the spectrum, the UK report found, some studies concluded that bioenergy will meet just up to 10 percent or less of current energy demands. Other studies projected that, in ideal situations, the true contribution could be as high as 60 to 150 percent. Most estimates fell in the middle ground.

The low-end estimates had several features in common: They assumed that little-to-no land will be set aside for energy crops, that there will be little or no change in crop yields, and and that non-crop sources of biomass—such as miscanthus and switchgrass— will be minor sources of bioenergy. At the other extreme, the high biomass estimates forecasted that vast amounts of land currently used to raise food crops could be converted to biofuel production, an unlikely scenario.

The Virgin Voyager, the UK’s first biodiesel train
(Photo: Adrian Dennis/AFP/Getty Images)

The report favored the most likely scenario: moderate estimates, which predict that biomass will meet between 10 and 60 percent of global energy demand.  These estimates projected that increased yields will improve supplies of both food and energy crops, which in turn will minimize conflicts over land use. Many models also assumed that energy crops could be grown on land that is too marginal for farmland.  

Many other variables push estimates in one direction or another. Some models predict a global shift to a more western-high meat diet, a move that would turn more land that could be used for energy crops into feedlots and pasture. On the other hand, one study suggests that biomass potential would more than double if global meat consumption declined.

Water is another important variable. While most of the models assume growing energy crops solely with rain water, sustainability would likely require effective management of water resources and more drought tolerant crops.  

In the end, the report didn’t end the controversy or answer the most pressing questions. But it successfully identified the key parameters that will drive the discussion in the coming years. When current unknowns such as crop yields and land use come into focus, the future of bioenergy will be much more clear.  As the authors conclude, “If biomass is believed to be a necessary component of the future global energy supply…then more needs to be done to make it a sustainable option.”




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