Enduring Understanding:

• Humans use energy from a variety of sources, resulting in positive and negative consequences.

Learning Objective:

• Describe the effects of the use of biomass in power generation on the environment.

Essential Knowledge:

• Burning of biomass produces heat for energy at a relatively low cost, but it also produces carbon dioxide, carbon monoxide, nitrogen oxides, particulates, and volatile organic compounds.  The overharvesting of trees for fuel also causes deforestation.

• Ethanol can be used as a substitute for gasoline.  Burning ethanol does not introduce additional carbon into the atmosphere via combustion, but the energy return on energy investment for ethanol is low.

Process

• Biomass stores energy from the sun, from photosynthesis

  • Remember the first law of thermodynamics: Energy cannot be created or destroyed

• Biomass is the leading renewable energy worldwide

  • Burning biomass is a direct source of heat for many in developing nations

  • Examples of biomass used for heat include:

    • Wood, peat, charcoal, crop residue, and manure

  • In this way, it can be used for heating, cooking fires, light, etc.

Types

Biofuel

• Biofuels are liquid fuels made from plant matter that can be used as substitutes for conventional petroleum products

• Ethanol

  • Made by fermenting plant-based starches into sugars and eventually alcohol

  • Typically mixed with gasoline to create ‘gasohol;’ 90% gas and 10% ethanol

  • E-85 and flex-fuel vehicles can run on a mixture of 85% ethanol and 15% gas

  • Switchgrass is being looked into as a better alternative

• Sources

  • Corn from the US, sugarcane from brazil, and sugar beets from both

Biodiesel

• Extracted and chemically modified oil from plants

  • Can be a direct substitute for diesel fuel

• Sources

  • Soybeans from Brazil and the US, oil palms from Southeast Asia, and rapeseed from Europe

• Using biofuels and biodiesel uses infrastructure that is already in place

• Straight Vegetable Oil (SVO) and algae could be more sustainable sources

Advantages and Disadvantages

Benefits

• Combustion in carbon neutral

  • This is modern carbon meaning the carbon was already cycling actively

  • Fossil fuels add carbon dioxide that was not actively cycling

• Potentially renewable is used sustainably

• Can be produced domestically

Drawbacks

• Net energy is low

  • More gasohol is needed to go the same distance

• Harvesting of crops for ethanol has potential for…

  • Increased use of fossil fuels in harvest

  • Increased deforestation

  • Reduction in fertility of agricultural land

Environmental Consequences

Positive Consequences

• Easily accessible

• Relatively inexpensive

• Can be used for heating and cooking easily

• Can produce electricity

  • This is, however, a longer process

Negative Consequences

• Pollutes the air

  • CO2, CO, nitrogen oxides, particulates, and volatile organic compounds

• Typically burned indoors, intensifying health effects of pollutants

• Overharvesting of trees for fuelwood and result in deforestation