Biomass is any renewable organic material that comes from plants and animals. Electricity that is generated from biomass is called biopower.
The sources for biopower are classified by their organic origins (agriculture, forestry, sewage) and by their physical form (solid, liquid, gaseous). Some forms of biomass are cultivated explicitly as a commercial energy source, such as switchgrass, a fast-growing perennial grass species in North America. Other forms of biomass are byproducts of forestry and agricultural operations, such as the collection and utilization of branches, foliage, and roots that remain after timber harvest.
Countries have distinct patterns of fuel use based on their geography, natural resources, level of technical development, and government policies. The government of Brazil aggressively promotes the use of ethanol and biodiesel as transportation fuels. As of 2022, a law requires that ethanol must comprise at least 27% of a liter of gasoline. The fermentation of sugarcane is the main source of ethanol. Sugarcane processing produces a pulpy fibrous material called bagasse that is burned to produce heating and electricity.
Countries with rich forest resources such as Canada and Sweden rely on trees for biopower. Wood products come in a variety of forms. Black liquor is a liquid form of energy produced as a byproduct of digesting pulpwood into paper pulp. It is gasified and then combusted in a gas turbine to generate electricity. Wood pellets are a solid fuel made by compressing lumber scrap, sawdust, or wood chips into small uniform pieces. Wood chips are small- to medium-sized pieces of wood produced by cutting or “chipping” larger pieces of wood. Pellets and chips are burned in a manner similar to fossils in which steam turbines power electric generators.
Refuse (municipal solid waste) contains energy-rich materials such as paper, plastics, leather, yard waste, and wood products. Waste-to-energy plants burn refuse and use the heat to drive steam turbines that power electric generators. Refuse is most common in countries such as Germany and the United States where landfilling waste is both expensive and faces strong, public opposition, creating a market for electricity generation.
China’s vast food production system generates biomass residues from the harvest of rice, corn, wheat, and other crops that are harvested to generate electricity in thermal power plants. China also has invested in waste-to-energy facilities that are concentrated in densely settled areas such as Guangdong province, the country’s most populous region.
What is the impact of biopower on climate change? At first glance, biopower might appear to be carbon neutral. The carbon removed from the atmosphere during the process of photosynthesis is released back into the atmosphere when the biomass is combusted. But the climate story of biopower (and biofuels) is much more complicated. Many bioenergy systems use substantial fossil fuels across their entire life cycles. Dedication of significant land area to grow biomass for energy will have large-scale impacts that ripple through land-use change, nutrients, cycles, water use, habitat for biodiversity, and potential competition for food, production, and other alternative uses.1
There is a range of estimates for the climate impacts of biopower. The most recent research suggests that using wood pellets produced from the harvest of standing trees and low-grade wood–is far from climate-neutral. Biopower carbon dioxide emissions are comparable to fossil fuels and they have very long atmospheric lifetimes, two attributes that would disqualify them as a climate-friendly, sustainable source of electricity.2,3,4
1 Heck, V., Gerten, D., Lucht, W. et al. Biomass-based negative emissions difficult to reconcile with planetary boundaries. Nature Clim Change 8, 151–155 (2018).https://doi.org/10.1038/s41558-017-0064-y
2 Dwivedi, Puneet, M. Khanna, and Madisen Fuller. “Is Wood Pellet-Based Electricity Less Carbon-Intensive than Coal-Based Electricity? It Depends on Perspectives, Baselines, Feedstocks, and Forest Management Practices.” Environmental Research Letters 14, no. 2 (January 2019): 024006. https://doi.org/10.1088/1748-9326/aaf937.
3 Natural Resources Defense Council, “A Bad Biomass Bet: Why the Leading Approach to Biomass Energy with Carbon Capture and Storage Isn’t Carbon Negative,” Issue Brief IB: 21-010-A, October 2021,https://www.nrdc.org/bio/sami-yassa/forest-biopower-far-carbon-neutral
4 Sterman, John, William Moomaw, Juliette N. Rooney-Varga, and Lori Siegel. “Does Wood Bioenergy Help or Harm the Climate?” Bulletin of the Atomic Scientists 78, no. 3 (May 4, 2022): 128–38. https://doi.org/10.1080/00963402.2022.2062933.