The diversity of potential sources is not the least of biomass’s advantages. Made up of organic matter from living organisms, the term encompasses wood materials and crops, crop by-products and wastes, waste from activities such as paper mills and sawmills, and the organic fraction of industrial, household and agricultural wastes.
Whether derived from plants, wood, fiber, waste, algae or other sources, biomass is one of the world’s most renewable resources. Its potential applications are just as versatile, from "traditional" uses in cooking, construction, heating, textiles and pharmaceuticals to other markets, including steam and power generation, gaseous, liquid and solid fuels of all types, hydrogen and alternative feedstock for chemical and plastic manufacturing (green chemistry).
Potential still checked by severe constraints
As plants grow, they utilize solar energy through photosynthesis and store carbon dioxide as the chemical bonds of carbon molecules. When converted into biofuels, for example, these carbon molecules will release their carbon dioxide during combustion. Yet the carbon dioxide released will be fixed again by other plants. So the use of biomass as an energy source is part of a natural short carbon cycle and, in theory, the amounts absorbed and released should more or less balance each other out.
On the other hand, biomass provides less concentrated energy than fossil fuels, which is not surprising since oil, gas and coal are in fact the result of biomass accumulated over very long periods. Thus, biomass delivers an average of five to seven gigajoules (GJ, or 1 billion joules) per million metric tons when it still contains water (wet biomass) and 17 to 20 GJ a metric ton when dry, versus 42 to 45 GJ a metric ton for crude oil.
Biomass’s low energy density and scattered sources push up the cost of logistics (collection, transportation, storage) and processing (pretreatment, conversion), and undercut carbon performance for the full life cycle. Thus, based on current technologies, only the most efficient — especially energy-efficient — cultivation and conversion processes perform well.
Consequently, the increased use of biomass as an energy source under conditions that are fully acceptable is only feasible in the medium and long term.
Not counting biofuels, biomass today meets about 10%(1) of the planet’s primary energy(2) needs, about a third of which from the traditional use of firewood, charcoal and manure, especially for heat and cooking in developing countries.
(1) International Energy Agency, World Energy Outlook 2008.
(2) Primary energy: Energy that exists in a naturally occurring form, such as coal, crude oil, sunlight and uranium, and that has not yet undergone any anthropogenic — derived from human activity — conversion or transformation process.