Wood energy
Wood energy is a renewable resource primarily derived from the burning of wood, which has served as a crucial source of heat for centuries. It encompasses various forms of biomass, including firewood, charcoal, wood chips, pellets, and sawdust, and is characterized by a complex composition of cellulose, hemicellulose, and lignin. The energy extraction process varies based on the type of wood used and its physical and chemical properties, such as moisture content and density, which influence caloric value and combustion efficiency.
Globally, wood energy is essential for over 2 billion people, especially in developing countries, where it is pivotal for heating and power generation. Environmentally, it presents advantages over fossil fuels, as it is a renewable energy source that can potentially reduce greenhouse gas emissions. The carbon dioxide emitted during its combustion is roughly equal to the amount released as the wood decomposes, making its net impact on carbon emissions minimal compared to fossil fuels.
Despite its benefits, the management of wood energy resources is critical to avoid environmental degradation, such as deforestation and desertification. The future of wood energy hinges on finding a sustainable balance and establishing effective policies that promote its development and utilization, especially in light of increasing concerns about climate change and energy security. As technologies advance and consumption patterns evolve, wood energy is expected to continue growing in relevance as a sustainable energy source.
Subject Terms
Wood energy
Summary: The burning of wood is the earliest source of energy for heating. Wood energy is a renewable resource. It is used by millions and it has great potential as a sustainable resource, given innovative energy conversion and agricultural technologies.
Wood energy is available through firewood (such as logs, bolts, and blocks), charcoal, chips, sheets, pellets, and sawdust. It is a form of biomass, which is the result of plants’ conversion of radiant (or solar) energy, carbon dioxide, and hydrogen (from water), via photosynthesis, into chemical energy, which the plants store in the form of complex molecules (polymers) with high energy content. The main polymers of biomass are cellulose, hemicellulose, and lignin. Cellulose is the main component of wood, about 50 percent of dry weight.
Characteristics of Wood Fuels
Wood fuels are characterized by extreme heterogeneity in composition, size, and shape, from logs to wood chips to sawdust, for example. The way these forms are converted into energy varies widely, depending on the physicochemical properties of the materials and the type of power plant that uses them. The aim of these operations is to obtain the most energy from the resource and convert it for greatest ease of use.
Wood fuels contain significant amounts of inorganic compounds: calcium, magnesium, sodium, potassium, silicon, and other elements that, after combustion for energy, remain in the ashes. The percentage of inorganic compounds varies, depending on several factors, such as the land in which the wood grew, the species of plant or tree from which it originated, and the organ or part of the plant (such as bark, roots, or stems and branches) from which it derives. These minerals and the ashes themselves can be repurposed for a range of uses, including soil amendments and agricultural applications.
Physical characteristics of wood that can have an impact on the process chosen to convert it into usable energy include its moisture and specific weight. Moisture content is important because, in addition to acting on the mechanisms of combustion, it has an influence on the chemical characteristics of wood and its specific weight. The amount of water in the wood is extremely variable at the time of cutting and can be affected by the species, age, part of the plant, and season in which it was harvested. The density is the most common indicator of the quality of wood fuel. In fact, the caloric value of the wood is directly proportional to its density.
An effective indicator of the value of an energy source is the energy content, which is defined as the amount of heat produced by complete combustion of a unit of weight of an energetic material. The caloric values of forest biomass vary greatly, depending on the physical characteristics and chemical composition of the material. A comparison of the heating value of wood and other fuels must take into account not only their caloric values but also the efficiency of the burning process. In modern systems, the efficiency of wood heat production ranges from 60 to 80 percent of caloric value, depending on several factors, including the efficiency of the boiler or stove.
Environmental Advantages
Wood energy is the main source of energy for more than 2 billion people, particularly in households in developing countries, and is used primarily for heat and power generation. It is an environmentally sound source of energy that provides a potential substitute for fossil fuels and has the ability to help reduce greenhouse gas (GHG) emissions. However, in some cases the shortage of suitable firewood has resulted in local populations damaging huge tracts of bush, which has led to desertification.
Wood energy has several environmental advantages over fossil fuels, first that it is a renewable resource, offering a sustainable, dependable supply when managed correctly. Carbon dioxide (CO2) released from burning wood is equal to the carbon wood releases as it rots, suggesting that the net impact of carbon emissions is null. The amount of CO2 emitted during the burning process is typically 90 percent less than when burning fossil fuels.
Wood energy shows significant promise in the near and mid-terms for reducing GHG emissions and meeting renewable energy goals quickly, cleanly, efficiently, and affordably. Wood fuel contains minimal amounts of sulfur and heavy metals. It is not a threat to acid rain pollution, and particulate emissions are controllable. Wood energy production and consumption have increased in recent years and are expected to continue to grow in view of concerns about climate change as well as energy security. Recent studies have reported a growth trend in final consumption of forest products, both for industrial and for energy uses. Finding a sustainable balance and establishing a sufficient policy framework to encourage the development and management of wood energy will, however, be paramount for the future of this resource. Three main factors should be considered in outlining the evolution of demand for this source of biomass energy: the development of final consumption of wood, the processes of globalization in the industry, and the replacement process.
The use of wood for energy is nevertheless supported by increasingly specialized production technologies, such as short rotation coppices and forestry that will tend to replace seminatural forests in the supply of raw materials coming into direct competition with alternative sources of biomass. One US study, for example, determined that American forests could sustainably produce 368 million dry tons of wood for energy per year.
About 2.1 percent of annual total energy consumption in the United States in 2022 was from wood and wood waste such as bark, sawdust, and paper mill residues. Some coal-burning power plants burn a combination of wood chips and coal to decrease sulfur dioxide emissions.
Bibliography
"Biomass Explained: Wood and Wood Energy." US Energy Information Administration, 12 June 2023, www.eia.gov/energyexplained/biomass/wood-and-wood-waste.php. Accessed 7 Aug. 2024.
Hoffmann, Peter, and Byron Dorgan. Tomorrow’s Energy: Hydrogen, Fuel Cells, and the Prospects for a Cleaner Planet. Cambridge, MA: MIT Press, 2012.
Shmulsky, Rubin, and P. David Jones. Forest Products and Wood Science. Chichester, UK: Wiley-Blackwell, 2011.
US Forest Service. “Woody Biomass Utilization Strategy.” www.fs.usda.gov/Internet/FSE‗DOCUMENTS/fsbdev2‗028768.pdf.