Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibers, chemicals or heat. Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum.

Plants use solar energy during photosynthesis, and store it as organic material as they grow. Burning or gasifying biomass reverses the process and releases the energy which can then be used to generate heat or electricity, or can provide fuel for transportation.
This idea is certainly not new - humans have been burning wood for cooking and heating for thousands of years and many still do. It is hard to say for certain how extensive the use of biomass is as an energy source today because some of the more traditional and non-commercial uses tend to be difficult to account accurately or go unreported. However, some statistics put its current contribution to the global energy mix between 10-14% (between 33-35% on average in developing countries and as high as 90% in the poorest nations).

There are several processes by which biomass is converted into a usable energy. The simplest, fairly inefficient and widely utilized in the developing world, is for the provision of heat, primarily for cooking and as a rudimentary source of lighting. Several African countries have developed improved versions of cookstoves that have been able to improve efficiencies of traditional cookstoves by about 200%. Some of these new cookstoves are able to capture over 40% of the potential energy in wood, compared to the less than 10% conversion rate of traditional models.

In colder climates especially in Scandinavia, Germany and Austria, domestic biomass fired heating systems are used fairly extensively. Some of these can achieve efficiencies of up to 70% with strongly reduced atmospheric emissions - considerable efficiencies over open fireplaces with chimneys due to the heat losses associated with chimneys.

Biomass is also used to generate electricity commercially in many parts of the world. This is called Biopower. There are four major types of biopower systems: direct-fired, co-fired, gasification, and small, modular systems.

Most of the biopower plants in the world use direct-fired systems. They burn biomass feedstocks directly to produce steam which is captured by a turbine, and then converted into electricity by a generator. The steam can also be used for certain manufacturing processes. In Malaysia, Thailand and Indonesia, wood scraps from lumber and paper industries are sometimes directly fed into boilers to produce steam for manufacturing processes and/or to heat buildings.

Many coal-fired power plants can use cofired systems to significantly reduce emissions, especially sulfur dioxide emissions. This also involves using bioenergy feedstocks as a supplementary energy source in high efficiency boilers.

Gasification systems use high temperatures and an oxygen-starved environment to convert biomass (usually wet organic domestic waste, organic industrial wastes, manure, sludges etc.) into a gas (a mixture of hydrogen, carbon monoxide, and methane). This gas fuels a gas turbine which turns an electric generator. For large-scale gasification projects the gas is thoroughly cleaned prior to its combustion.

The decay of biomass in landfills also produces methane, a greenhouse gas, which can be burned in a boiler to produce steam for electricity generation or for industrial processes. To release the methane, wells are drilled into a landfill. Then pipes from each well carry the gas to a central point where it is filtered and cleaned before burning.

A small, modular system is either a direct-fired, cofired, or gasification system that generates electricity at a capacity of 5 megawatts or less. This system is designed for use at the small town or individual household level. In India, there is widespread production of biogas from animal and other biomass wastes using this method. The gas has a variety of uses including cooking, lighting and some power generation. Wet biomass materials are very well suited for this system of biomass conversion.

Biomass is the only renewable energy source that can be converted directly into liquid fuels - biofuels - for transportation needs (cars, trucks, buses, airplanes, and trains). The two most common types of biofuels are ethanol and biodiesel.

Ethanol is an alcohol, the same found in beer and wine. It is made by fermenting any biomass high in carbohydrates (e.g. sugar cane, maize and corn) through a process similar to brewing beer. Ethanol is mostly used as a fuel additive to cut down a vehicle's carbon monoxide and other smog-causing emissions. Flexible-fuel vehicles, which run on mixtures of gasoline and up to 85% ethanol called gasohol, are now available. Brazil runs the largest program of commercial biomass utilization in the world.

Biodiesel, however, is not an alcohol but is an ester, which is similar to vinegar. Many vegetable oils, animal fats, algae, or even recycled cooking greases are used to produce biodiesel. It is used as a diesel additive to reduce vehicle emissions or in its pure form to fuel a vehicle.

Other biofuels include methanol and reformulated gasoline components. Methanol, commonly called wood alcohol, is produced through the gasification of biomass. After gasification, the resulting hot gas is sent through a tube and then converted into liquid methane. Most reformulated gasoline components produced from biomass are pollution-reducing fuel additives, such as methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE).

Biomass can also be chemically converted into liquid, gaseous and solid fractions by a process called pyrolysis. It occurs when biomass is heated in the absence of oxygen. The liquid product is called pyrolysis oil which can be burned like petroleum to generate electricity.

Pyrolysis oil has its advantages: it's easier to transport and store than solid biomass material, and it can be refined in ways similar to crude petroleum oil. Some coal plants may even use powdered coal mixed with pyrolysis oil to economically meet new environmental regulations.

A chemical called phenol can also be extracted from pyrolysis oil. This is used to make wood adhesives, molded plastic, and foam insulation, which are currently made from petroleum and natural gas - nonrenewable energy resources.

Other industrial uses of biochemicals are being researched, including the use of bioenergy feedstocks to cost-effectively manufacture high-volume chemical building blocks. A US government agency has developed an inexpensive process that can convert waste from landfills and paper mills into environmentally-friendly, biodegradable products, such as gasoline additives.

Generating electricity from biomass has typically been about 20% efficient. Technological improvements, such as converting biomass into gas and then burning it in a gas turbine, have significantly improved this efficiency.

Cogeneration (known as Combined Heat and Power in Europe) plants run on biomass, others on fossil fuel, with the common thread being increased efficiency.

Cogeneration plants typically burn a fuel to create electricity but rather than just venting the "waste" heat into the environment they hold onto it and use it to heat buildings and water. Some industrial plants like paper mills can use the residual steam, after it has turned a turbine, instead of boiling water with an entirely different system. Cogeneration plants can be tailored to a variety of sizes, from micro-single farm operations to standard electric utilities that supply heat to a whole town.

Although other renewable energy technologies are actually more efficient in exploiting the sun's energy - biomass captures less than 1% of the sun's available energy - biomass does have the added advantage of being easily stored for future use. Advances in technology are increasing the efficiency with which the stored energy in biomass is converted to useable form. In addition, the costs of producing energy from biomass are currently quite competitive.

A greater reliance on biomass could also mean a much-needed source of income for farmers and rural dwellers. However, there are some concerns for increasing global reliance on biomass as a power source.

Many current sources of biomass energy are also in demand for other purposes - for example, wood to make paper, or crops to feed animals and people. One possibility is to expand the use of agricultural or industrial residues that are considered waste products anyway. For example in the United States, the paper industry is able to meet 50% of its energy demand for heat and electricity using sawdust, scrap wood, and pulping waste. Denmark has made its largest agricultural waste product - straw - into a viable energy source that provides over 7% of its energy.

Some biomass supporters have suggested growing lower-grade crops - such as perennial grasses and fast-growing trees - specifically for energy use, but this prospect could create additional competition for an already limited supply of agricultural land. There will also be increased demand on water and soil resources, agrochemicals and biodiversity. Of course, it is possible to grow and harvest biomass crops more sustainably. For example, the perennial grasses such as switch or elephant grass can actually help control erosion. And rather than devoting entire fields to biomass stock, these crops can be grown in between other crops on existing fields which can actually be beneficial.

Biomass is the fuel most closely associated with energy-related health problems in developing countries. As dangerous as outdoor air pollution is to health, it is believed, indoor air pollution actually poses a greater health risk on a global scale. Exposure to particulates from biomass or coal-burning causes respiratory infections particularly in children and the elderly. Carbon monoxide has also been implicated in problems in pregnancy. Government and international organizations are beginning to look at these problems more closely and are promoting several solutions including better ventilation systems in huts and switching to alternative fuels such as gas and charcoal briquettes in several Asian countries.

Some experts see a much greater role for biomass energy use in the future, given its unique benefits such as ease of use and local adaptability. A greater reliance on biomass as part of a sustainable local and national energy system should assist in the development of rural areas through increases in rural incomes.

Additional Resources

US Department of Energy: Biomass
List of websites and reports dealing with biomass.

National Renewable Energy Laboratory
A branch of the Department of Energy. Details projects to develop and integrate biochemical and thermochemical conversion processes to create energy with biomass

National Biomass Initiative
A multi-agency effort to coordinate and accelerate Federal bioenergy research and development

IEA Bioenergy
An organization set up by the International Energy Agency to encourage the spread of information between countries with bioenergy programs.

Biomass Energy Research Association
An association of biofuel researchers promoting the education and research of renewable biomass energy

Renewable Energy Policy Project
A simple, easy-to-follow analysis of biomass as a potential energy source.