Throughout history, humans have used fuels made from plant and animal matter for heating and cooking. Today, technological advances and society's increasing demand for energy have led to an expanded role for these biomass fuels. The term bioenergy, or biomass, means any plant-derived organic matter available on a renewable basis, including crops and trees, agricultural food and feed crops, agricultural crop wastes and residues, wood and wood wastes and residues, aquatic plants, animal wastes, municipal wastes, and other waste materials. These sources can provide energy in the form of electricity, heat, steam and fuels and provide about three percent of all the energy used in the United States.

Biomass fuels get their energy from the sun. Photosynthesis converts solar energy striking the leaves of plants into chemical energy, which is stored in the plants themselves. Animals that eat plants store some of this energy in their bodies; some of it is also ultimately stored in manure and other wastes. Biomass fuels are a renewable resource because they can be replaced fairly quickly (within a human lifetime) without permanently depleting Earth's natural resources. By comparison, fossil fuels such as petroleum and coal, require millions of years of natural processes to be produced. Therefore, drilling for petroleum is considered a nonrenewable process as it depletes Earth's resources for thousands of generations.

Wood
Wood was once the main energy resource used during the early history of the United States, but now it plays only a small role in meeting the nation's energy needs (3%). Still, in certain parts of the country, including Wisconsin, wood provides people with a cheap and plentiful source of energy for heating. About 20 percent of U.S. homes get some heat from burning wood, while about four percent use it as their primary fuel. The forest products industry (pulp and paper manufacturers, mills, etc.) consumes almost two-thirds of all fuel wood.

Wood gets its energy from the sun. Photosynthesis converts sunlight that strikes the tree leaves into chemical energy, which is stored in the wood itself. Wood is a renewable resource, which means that additional resources can be grown to replace any wood that is cut down.

Wood for heating is sold in units called cords. A cord is a stack of wood 8 feet long, 4 feet high, and 4 feet wide (128 cubic feet). A face cord is a stack 8 feet long, 4 feet high, and 12 to 16 inches wide (32 to 40 cubic feet). A cord of hardwood such as maple, oak, or hickory may contain twice as much energy as a cord of softwood such as pine or balsam fir. This variation in energy is because a cord of hardwood weighs up to twice as much as a cord of softwood. For example, about twelve cords of white pine are needed to heat an average home is Wisconsin for the year, while only about seven cords of white oak are needed to provide the same amount of heat. These figures assume that the average Wisconsin home needs 80 million Btu for heating each year and uses a woodstove with an efficiency of 50 percent.

Forests cover about one-third of the total land area of the United States (737 million acres). About two-thirds of this forest is productive enough to grow commercially valuable trees. About 15.4 million acres (44 percent) of Wisconsin's land area was covered by forest in 1983, with about 96 percent of this forest land used for growing trees commercially. The potential amount of wood energy from Wisconsin sources is about 200 trillion Btu, an amount that could heat about 2.5 million average-sized Wisconsin homes each year.
          Photo Courtesy of NREL

Methods for harvesting wood range from simply cutting down a tree with an ax or saw to removing all the trees from a large area (clear-cutting) using chainsaws and other heavy equipment. Other than drying, wood does not require much processing before being used as a fuel. Some homeowners may burn wood pellets that are manufactured from finely ground wood fiber, which requires more processing. Wood pellets for burning in power plants are made by harvesting and shredding whole trees. Pellet fuel can also be made from sawdust and shavings leftover from processing trees for lumber and other wood products.

About two million cords of wood are cut and burned for energy in Wisconsin each year. The total amount of wood energy used in Wisconsin in 2003 was 52 trillion Btu, about three percent of all the energy used in the state. Worldwide, one-half of all wood that is cut down is used for fuel, while in developing countries 90 percent is used for fuel. Sweden is a world leader in using wood as an energy source; most of the wood they use is for fueling district heating plants.

Certain electric power plants in the United States and the rest of the world burn wood to generate electricity. Like coal and fuel oil, wood is burned in a boiler that heats water into steam. The steam then spins a turbine connected to an electric generator. Power plants usually burn wood along with other fuels; they rarely burn wood exclusively. Over 300 power plants in the United States burn wood to produce and sell electricity. Small (5-25 megawatt) wood-burning plants located near wood fuel sources provide four percent of the electricity used in New England. The Bay Front Plant in Ashland, Wisconsin, and the French Island Plant in LaCrosse, Wisconsin, burn significant amounts of wood to generate electricity. Together these power plants burn a total of over 338,000 tons of wood per year.

Wood is a major fuel source for industries that produce wood products. About 1,000 wood-fired power plants currently operate in the United States, two-thirds of which are owned by industries such as the paper and pulp industry. Many of these industries use wood energy to provide steam, heat, and electricity (this multiple use is called cogeneration).

In parts of the U.S. where wood is plentiful, many rural homeowners burn wood for space heating. Roughly 500,000 homeowners in Wisconsin burn wood to meet some or all of their space heating needs. Wisconsin residents use about one-half of all wood fuel, while the other half is used for commercial and industrial purposes.

Wood is also used to make building materials, pulp, and paper. Other uses include consumer products (e.g., toys, sporting equipment, pencils, and musical instruments) and chemicals. Wood and its derivatives are used in as many as 10,000 products. Generally, wood harvested to make wood products does not come from the same sources as wood harvested for energy.

Agricultural Wastes
Agricultural wastes are plant parts left over after farmers have harvested their crops. These wastes include stalks, husks, prunings, straw and corn cobs. Agricultural wastes can be collected, dried, and burned to produce energy. Burning these wastes in small power plants can provide a convenient source of energy for rural areas and developing countries. The ash that remains can sometimes be used as a fertilizer. Agricultural wastes are used to produce energy in many parts of the world. In Hawaii and Brazil, bagasse, a residue left over after sugarcane is harvested and processed, is burned in power plants to produce electricity. In Denmark, straw is burned to produce heat for farms. Wisconsin produced about 1.7 trillion Btu of energy from crop residues in 1994, an amount equal to the energy used to heat about 20,000 average-sized Wisconsin homes.

Alcohol Fuels
Ethanol is ethyl (grain) alcohol (CH₃CH₂OH). It is made by an advanced distillation process from crops and vegetable matter such as corn, sugar beets, or grasses, or by fermenting by-products of cheese and paper manufacturing. With many Wisconsin farmers growing corn, there is potential for ethanol plants in Wisconsin, with others being proposed and planned.

There are three primary ways that ethanol can be used as a transportation fuel:

• As a blend of 10 percent ethanol with ninety percent gasoline known as E10 or gasohol (which you now see at most gas stations)
• As a component of reformulated gasoline, directly and/or as ethyl tertiary butyl ether (ETBE), or
• A mixture called E-85 that consists of 85 percent denatured ethanol blended with 15 percent gasoline; E-85 does not burn well in conventional vehicles, but flexible-fuel vehicles (FFV) are designed to run on all blends up to 85 percent.

View a list of stations in Wisconsin that carry E-85

Liquid ethanol can be used as a fuel when blended with gasoline or when in its original state. Ethanol can be used to increase octane levels, decrease engine emissions, and can extend the supply of gasoline. About 1.6 billion gallons of ethanol are produced annually in the United States. Each bushel of corn processed yields 2-4 gallons of ethanol  Photo Courtesy of NREL                           along with several valuable by-products. The first blends in the 1970's were 10% by volume (E10), while a blend of 85% by volume (E85) was introduced in the late 1990's. About one-third of Brazil's automobiles are powered by pure ethanol produced from sugarcane.

The U.S. produced about 2.8 billion gallons of ethanol in 2003. Midwestern states produce most U.S. ethanol because these states grow large amounts of corn. Very little ethanol produced in the U.S. is made from biomass; it is cheaper to manufacture it from natural gas. Analysts estimate potential ethanol production in Wisconsin to be over 900 million gallons annually - enough to meet a large portion of the state's transportation needs. Wisconsin's first ethanol plant opened in 1996 near Plover where it manufactured ethanol from cheese whey, vegetable waste, and paper waste. This plant no longer operates.

View Ethanol Biorefinery Locations

Methanol (wood alcohol), which is similar to ethanol, is the required racing fuel for major sport events such as the Indianapolis 500. Aside from being a component of fuel, methanol is also widely used as a solvent and in industrial applications. Methanol can be produced by heating wood in an enclosure that has little air and then using chemicals to convert the gases given off by the heated wood into a liquid. Methanol (CH₃OH), made by a non-natural destructive distillation of wood, is toxic and can cause blindness in small amounts, and death in larger amounts.

Both ethanol and methanol can be used to run cars, trucks, and buses, however, most motor vehicle engines that burn gasoline would need to be modified to use alcohol fuels.
                                                                                                                                                     

Animal Wastes
Animal waste products such as manure have long provided biomass fuel for rural societies. People in developing countries often burn dried manure for heating and cooking. Manure can also be placed in tanks called anaerobic digesters, where it is broken down by bacteria and various chemical processes to produce biogas (60% methane and 40% carbon dioxide). Small-scale production of biogas can provide fuel for space heating and cooking, while larger-scale production of biogas can generate electricity or provide heat for manufacturing processes. A number of small biogas-fueled power plants are in operation throughout the world. Plants in the U.S. use manure from farms and cattle feedlots. For example, one plant in California that burns cattle manure supplies electricity to as many as 20,000 homes. A small number of Wisconsin farms generate biogas from manure, although the state's dairy farms have the potential to produce more.
              
             Photo Courtesy of NREL

Municipal Solid Waste (MSW)
Waste disposed of by residents and businesses, called municipal solid waste (MSW), can provide a source of fuel. A large percentage of this waste is made up of organic materials such as wood, paper products, food waste, and yard waste. Therefore, some MSW is a form of biomass fuel. Specially equipped waste-to-energy power plants can use MSW to produce electricity or heat. The waste is separated and non-combustible materials are removed before the remaining waste is taken to the power plant to be burned. 116 waste-to-energy facilities in the United States burned about 100,000 tons of waste per day. Another source of fuel from MSW is landfill gas. This gas in produced by the breakdown of organic material. Landfill gas, which is similar to natural gas, can be added to natural gas pipelines or burned in small power plants. One-third of these facilities are located in California. Some also exist in Wisconsin. Wastewater treatment facilities can also be utilized to generate energy, through anaerobic digestion, in the form of methane gas. The methane gas can then be used to supplement natural gas which would normally be used to heat digester tanks which break down waste and kill pathogens in the waste. The benefits of this technique include odor control, waste reduction and valuable byproducts (mulch). McCain Foods in Plover, Wisconsin built a wastewater treatment facility on site that converts waste into energy. In 2002 this technology saved the company $50,000 in fuel bills. A plant in Madison, Wisconsin reports $370,000 in electrical savings and $75,000 in gas heating.