NC State Extension Publications


This publication defines addresses many of the questions often asked about biomass-based energy, the associated technologies, and producing woody biomass. These questions and their answers will help you understand terms and concepts commonly associated with biomass energy.

Woody Biomass Defined

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Q: What is biomass?

A: It is a term for living or recently living plant material harvested and used for energy production.

Q: What is woody biomass?

A: Woody Biomass is any biomass from woody plants and includes wood residues from manufacturing, logging residues following harvesting, trees harvested for fuel, usually because they have no higher commercial value, or trees harvested from dedicated energy tree crops.

Q: Is there an abundant supply of woody biomass in North Carolina?

A: To date, establishment of dedicated wood energy crops has been minimal. However, some studies estimate that there may be as much as 9 million green tons of woody biomass that can be produced during harvesting operations annually. In addition are un-quantified volumes of wood from land 3 clearing as well as materials from tree trimming and other urban forestry activities.

Q: What are the most frequently used units of measurement for woody biomass?

A: Woody biomass is usually measured in green tons or dry tons, but may also be measured in energy content such as btu’s (British Thermal Units). Energy content per unit of weight varies by species, but especially by moisture content, which may be as high as 40- 50% for “green chips” from live trees. Green tons include moisture. Dry tons are the equivalent weight oven dried.

Dedicated Energy Wood Plantations

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Q: What are dedicated energy plantations (also called “purpose-grown energy plantations”?

A: Dedicated energy plantations, also referred to as short-rotation woody crops or purpose-grown energy plantations, are densely planted stands of fast-growing species such as hybrid willow, hybrid poplar, or cottonwood planted solely for the purpose of being harvested entirely for energy. Because claims have been made that these crops can be harvested in as few as three to five years after planting, interest is high. Although research is still needed to document establishment costs and production rates for specific species on specific sites, it is generally assumed that because establishment and management costs will be high, they will not produce a positive economic return until wood-energy markets are relatively mature bringing higher prices for woody biomass.

Q: With abundant forestland in North Carolina and the South, why establish dedicated wood plantations?

A: Woody biomass co-produced from the forest during conventional harvesting is subject to the variability of timber markets, and as a feedstock, woody biomass thus produced will be variable in physical and chemical properties depending on the mix of species being harvested. Woody biomass from dedicated plantations will be more uniform in characteristics, which are especially important for ethanol production and can be harvested without consideration of other timber markets.

Q: Where will dedicated energy wood plantations be established?

A: In theory, dedicated energy wood plantations can be established anywhere. However, establishment practices are very intensive and agriculture-like, thus it is widely believed that they will mostly be established on marginal agriculture lands rather than in recently harvested forests. These plantations can also be established on lands where food crops cannot be grown such as brown fields, municipal waste treatment spray fields, or agricultural land receiving animal lagoon effluents. is possible. However, wood gasifiers are now commercially manufactured that can remove a home or business from the electric grid. Where substitution makes the most sense is where biomass can be used in technologies where minimum adaptation is required or where substitution of biomassusing technology provides a significant benefit such as long-term cost savings. The most readily feasible opportunities for substitution are in gasifiers or boilers.

Q: Can biomass be used with other fuels?

A: Biomass can be mixed with other fuels in gasifiers and boilers depending on the specific design and fuels being mixed.

Q: What is the difference between biofuels, biopower, and bioproducts?

A: These terms refer to three generally different end uses — transportation, electric power or heat, and products such as chemicals and materials. "Biofuel" is short for biomass fuel. We use the term biofuels for liquid transportation fuels produced from biomass, such as ethanol, bio-oil, and biodiesel. "Biopower" refers to biomass power systems that generate electricity or industrial process heat and steam, such as combined heat and power (CHP) systems. "Bioproduct" is short for biomass products and can be used to describe a chemical, material, or other product.

Q: Why is there such an early emphasis in power production from biomass?

A: Whereas commercial-scale production of transportation fuels may be a few years away, electricity can easily be made today using co-firing in gasification systems or boilers or by using biomass in dedicated biomass boilers or gasifiers.

Q: What is co-firing?

A: Co-firing refers to the blending of biomass with coal a conventional coal-fired power plant boiler or gasifier. Between 5% and 15% biomass (by heat content) may be used in such facilities. Although simple in concept, the blending can present challenges depending on the plant technology being used. For example, where coal is pulverized prior to combustion, high-moisture wood chips have to be dried and sometimes sizereduced prior to pulverization.

Q: What is gasification and are there any advantages to these technologies?

A: Gasification of biomass is where biomass is heated in a reduced oxygen environment so that a combustible synthetic gas is produced instead of direct combustion of the biomass. The gas can then be used to make electricity or liquid fuels depending on the technology used.

Q: What are wood pellets and what are they used for?

A: Sawdust and green wood chips from in-woods harvesting operations are loose and not very energy dense (heat value per unit volume). Densifying woody biomass by compressing it into solid forms such as pellets, bricks, or briquettes improves energy density for shipment and handling for some systems. Some stoves and furnaces are designed for pellets and there has especially been recent interest in shipping pellets overseas to power plants. Pellets can be bagged for home-size stoves or shipped in bulk. Bagged pellets are also used for animal bedding and litter.

Q: What is an RPS or REPS?

A: RPS (or, in NC an REPS) is a 7 Renewable Portfolio Standard. In general terms, it is state legislation that requires public electric utilities to generate a portion of their power with renewable sources although they may contain other provisions. In August 2007, the North Carolina General Assembly passed the Renewable Energy Portfolio Standard that requires public utilities to generate a minimum of 7.5% renewable retail electricity by 2021. Rural electric coops have a somewhat different requirement. They can meet another 5% by renewable energy or energy efficiency measures. It is thought that in North Carolina most of the renewable requirement will be met with wood biomass.

Q: What has transpired in North Carolina since passage of the REPS?

A: Passage of the bill has resulted in wood availability studies, site studies for private electric plants and permitting for co-firing studies by the electric utilities, and studies on co-firing techniques.


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Q: How is woody biomass harvested?

A: In most cases, woody biomass is harvested by adding a whole-tree chipping machine to the mix of conventional logging equipment during an otherwise conventional-product harvest. Some loggers also use tub grinders to reduce material to a smaller size. Limbs, tops, small trees, and otherwise nonmerchantable trees are collected and chipped. This can also be done during thinnings where normal merchantable stems to be thinned are harvested for conventional markets and tops and limbs are chipped. Woody biomass fuels can be produced by using tub grinders to grind up stumps, tree pieces too large for in-woods chippers, and other concentrated piles of debris such as from storms. Not all woody biomass using facilities will accept tub grinding material due to dirt content.

Q: Will woody biomass markets result in stems normally used for conventional forest product markets being used for energy?

A: Woody biomass is likely to always be among the lowest-value forest products, thus it would not make economic sense for a logger or buyer to chip stems salable for lumber, veneer, poles and pilings, or chip ‘n saw. However, it is conceivable that where demand for woody biomass is strong, it may compete for pulpwood or oriented strand-board.

Q: Will markets for woody biomass result in greatly increased harvesting including clearcutting?

A: Normally, because woody biomass is co-produced during logging for conventional products, little increase in harvesting levels would be expected. An exception might be harvesting unmerchantable degraded stands where woody biomass energy markets might allow a landowner to remove the poor stems to create a productive stand. Woody Biomass and Forest Health

Q: Will harvesting woody biomass improve or reduce forest health?

A: Harvesting for any products should be done with forest health in mind. Considerations include avoiding or limiting damage to soils and remaining standing trees. However, harvesting woody biomass provides opportunities to improve forest health by providing markets for diseased, damaged, off-site species, and otherwise cull trees that utilize space and resources. 9 Removal of these trees leaves site resources for the best quality and healthiest trees.

Woody Biomass and the Environment

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Q: Will use of woody biomass for energy improve or degrade air quality?

A: Fossil fuels, especially coal that is especially used for electricity production, produces sulfur and nitrogen compounds (referred to as SOx and NOx that are compounds associated with acid rain). Combustion gasses from woody biomass are typically relatively low in these compounds. However, when burned in older boilers not properly retrofitted, woody biomass can produce elevated levels of particulates.

Q: How can use of woody biomass contribute towards climate change solutions?

A: The principal greenhouse gas thought to be responsible for climate change (global warming) is carbon dioxide, a product of combustion. Use of woody biomass also produces carbon dioxide. However, biomass is grown by using atmospheric carbon to develop plant tissue. Thus, woody biomass is considered to be “carbon neutral” and can replace use of fossil fuels where carbon that has been sequestered for thousands of years is released into the atmosphere when burned. Some recent studies have disputed the notion of carbon neutrality of wood by in part noting that in some places it takes many years for standlevel carbon equal to pre-harvest levels following harvest. Only Life Cycle Analyses of specific scenarios can quantify impacts of using biomass for energy.

Q: Are there risks to the environment associated with harvesting of woody biomass?

A: There are no common documented environmental problems associated with harvesting woody biomass. However, because harvesting of woody biomass from the forest, especially clearcuts, represents higher rates of utilization, questions have been raised regarding maintaining longterm site productivity and other questions have been raised regarding structure and course woody debris for wildlife habitat. Adequate data for specific forest types and wildlife species has been identified as a research need. Generally speaking, it is assumed that following established Best Management Practices for timber harvesting will adequately protect water quality. However, some state have been developing BHGs to mitigate potential environmental impacts of biomass removal.

Q: What are BHGs?

A: BHGs are Biomass Harvesting Guidelines designed to maintain or improve ecosystem attributes when biomass is harvested. Currently they are state-based and have been developed only for a few states. Provisions differ from state to state, but most restrict the volumes of biomass that can be removed. A common complaint regarding BHGs is that little research has been conducted documenting their need or benefit.

Q: What is Life-Cycle Analysis (LCA)?

A: In general terms, LCA is a technique to assess environmental impacts associated with all the stages of a product's life fromcradle- to-grave. In the case of energy, LCA assesses the complete energy of carbon impacts of a scenario. Market Value of Woody Biomass

Q: Can a landowner expect to make a lot of money selling woody biomass?

A: Because woody biomass is expected to be a relatively low-valued forest product, income from biomass will be low compared with most conventional forest products. However, when produced during conventional harvests, income will be in addition to that from conventional forest products. An exception will be dedicated wood-energy crops, if established where energy wood is the sole intended market.

Q: If woody biomass remains a relatively low-valued forest product, why would a forest landowner be interested in seeing these markets develop?

A: First, with the exception of dedicated energy plantations, income is usually in addition to that for conventional forest products. Second, when woody biomass is removed during final harvests, landowners can often avoid site preparation costs because of better utilization. Last, because diseased trees, crowded trees, off-site species, and otherwise undesirable trees can be removed as woody biomass, the productive capacity of the stand can be focused on the best trees resulting in higher volumes of high-value stems.

Biomass and State Economic Development

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Q: It seems use of biomass is just a substitution for other fuel sources. Can it really contribute to the state’s economic benefit?

A: For some forms of energy, biomass is indeed a substitution for other fuel sources – especially fossil fuels. However, North Carolina imports most energy from out-ofstate including gasoline, most diesel, natural gas, and coal. By using biomass produced in the state and converting it to energy in state-located facilities, new jobs are created and state, county and municipal tax revenues are improved.

Q: Is there a “green” economic benefit to the state in using biomass?

A: It is expected that the trend towards federally-funded incentives for green energy including biomass will continue and even increase. Biomass projects will allow the state to capture increasing shares of these available Federal dollars. The biomass-related energy industry will participate in and benefit from carbon markets if they develop which will result in private dollars flowing to projects. Impacts to Traditional Forest Industry

Q: How will development of markets impact traditional forest industry?

A: Paper mills purchase or harvest woody biomass in the form of dirty chips for boiler fuel. Both pulpwood and Oriented Strand Board (OSB) utilize low-value stems from the forests. In immature energy markets for woody biomass, there may well be competition for boiler fuel and OSB, but little competition for pulpwood. However, with traditionally low prices for pulpwood and with increasing energy-wood markets, it is reasonable to assume there may be competition in time in some regions. However, in areas with little or no markets for pulpwood, woody biomass for energy may be the only markets for low-value wood and even thinnings.

Marketing Considerations and Safeguards

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Q: Are there any precautions that a landowner should observe when selling woody biomass?

A: Forest landowners should always market timber in an intelligent and professional way. This means being informed regarding the volumes and quality of timber to be sold. They should especially be informed regarding the volumes of timber to be sold for each product class such as pine and/or hardwood sawtimber, chip ‘n saw, pine and hardwood pulpwood, material for oriented strand board, and woody biomass for energy. Buyers purchase timber regularly whereas the typical landowner may sell timber only once or several times during his or her ownership. It is often wise to have a professional consulting forester represent a landowner as an agent during timber sales so that equal knowledge is on both sides of the transaction. A landowner should be certain that because of different values for different product classes, a landowner is receiving correct values for volumes sold. As an example, a landowner would not want to receive biomass prices for material harvested and actually sold as chip ‘n saw. Landowners should make sure buyers are reputable and follow proper harvest practices.

Q: What factors may limit marketability of biomass on my forestland?

A: Some limiting factors are common to other forest products and some are mostly limiting for woody biomass for energy. First, there have to be local markets. Because woody biomass is a lower-value forest product and because about half the weight of green chips is water, woody biomass is not often economically hauled more than about 50 miles depending on delivered prices and the cost of diesel fuel for harvesting and transportation. The total value of the sale of all products and current market needs of local wood products industries determines the attractiveness of a potential sale offering to buyers. If there is a limited volume of woody biomass on your timber sale, it may not be worthwhile for a logger to bring in additional equipment just to harvest biomass.

Q: If a buyer is only offering a couple of dollars or even nothing per ton for woody biomass, am I as a landowner being taken advantage of?

A: Stumpage (the payment received by a landowners for timber products) is a residual value. That is, money available to pay the landowner by the buyer is essentially what is left over to the buyer after paying harvesting and transportation costs. Because biomass in less well developed markets may be the lowest value 15 product in the forest, there are times when the buyer can afford to pay little of nothing. In these cases, the value to the landowner of the biomass is reduced site preparation costs and often improved forest health. Because stumpage for biomass may remain lower than for other products, a landowner will want to be certain that (1) he or she is not receiving biomass stumpage when the stems were actually used for higher-value products, or (2) the logger did not chip potentially higher-value stems for biomass because of quotas or other factors. Working with a Registered Forester to avoid these situations is recommended.

Prepared by

Dennis Hazel, Extension Specialist and Associate Professor

Extension Forestry

NC Woody Biomass

“Nature’s renewable energy!”

Extension Forestry

Campus Box 8008

NC State University

Raleigh, NC 27695-8008


Extension Specialist and Associate Professor

Find more information at the following NC State Extension websites:

Publication date: Jan. 1, 2013

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