6.12 Energy from Biomass

What is biomass energy?

Biomass is renewable organic material from plants and animals (wood, crop residue, animal waste, dedicated energy crops) burned or converted for energy. It's considered carbon-neutral in theory because plants absorb CO2 while growing, offsetting emissions from burning — though land clearing and processing add real-world emissions.

Forms of biomass energy

Common sources include fuelwood, charcoal, methane biogas from decomposing manure/waste in anaerobic digesters, and biofuels like ethanol (from corn or sugarcane) and biodiesel (from vegetable oils). Many developing countries rely heavily on wood/dung for cooking and heating, while developed nations blend ethanol into gasoline.

Advantages and drawbacks

Biomass is renewable, reduces waste, and can use agricultural residues. Drawbacks: burning releases particulates and CO2, large-scale crops (like corn ethanol) compete with food production and cause deforestation/habitat loss, and net energy return on investment (EROI) can be low once farming, harvesting, and transport are counted.

Key terms

Biomass

Renewable organic material (wood, crop residue, animal waste, energy crops) used as an energy source.

Carbon-neutral (biomass)

The idea that CO2 released from burning biomass is offset by CO2 absorbed during plant growth.

Biogas

Methane gas produced by anaerobic digestion of manure or organic waste.

Ethanol vs. Biodiesel

Ethanol: alcohol fuel from fermented corn/sugarcane. Biodiesel: fuel made from vegetable oils or animal fats.

Drawback of large-scale biofuel crops

Can compete with food production, drive deforestation, and have low net energy return (EROI).

Try an AP-style question

Why is biomass sometimes called carbon-neutral?

1. It captures CO₂ from engines
2. It is made from fossil fuels
3. Regrowing plants reabsorb the CO₂ released
4. It releases no CO₂ when burned