Wood (as energy source)

Biomass receives and stores energy from the sun. When burned, this energy is released as heat. Wood fuel (commonly referred to as fuelwood) serves a variety of heating purposes although the most common fuelwood-based practices around the world cooking and heating—especially in developing nations.

Calculating how much wood is harvested and burned each year is difficult to determine because fuelwood collection and use occurs predominantly through informal practices. As a result there is a dearth of precise data on wood energy use. This stands in contrast to non-biomass energy sources such as oil and natural gas, which have been subject to more in-depth analysis.

According to the United Nations Food and Agricultural Organization (FAO), biomass accounts for roughly 30 percent of the total energy consumed in developing nations-with fuelwood accounting for approximately half of this amount or 15 percent of the total energy. Other common types of biomass include agricultural matter and animal dung. In some countries, dependence on fuelwood is much higher. For example in Nepal and countries in SubSaharan Africa, fuelwood accounts for roughly 80 percent of the total energy requirements.

Developed nations use fuelwood to a much lesser extent, although fuelwood contributes to between 12 to 18 percent of total energy needs in Scandinavian and Central and East European countries primarily because of heating practices during cold winters. Still, dependence on fuelwood is most common in developing nations with the FAO estimating in 1998 that 50 percent of the world's fuelwood was consumed in five countries: Brazil, China, India, Indonesia and Nigeria.

Wood as a source of energy varies in its heating potential. Two major factors determining heat potential are wood density and dryness. Density is determined by tree species type. The potential heat content per kilogram is roughly equal between all types of wood so it is the density of that wood which influences its heat producing capacity. Broadly speaking, wood either comes from softwood or hardwood varieties. Softwood tree species include many conifers while hardwood species are typically broadleaf trees. Softwood trees are typically less dense than slower growing hardwood tree species and are therefore less desirable for fuelwood. There are some hardwoods such as Aspen or Poplar with lower density wood and some softwood trees like Western Larch and Yew with higher density fuelwood. Dryness is another important factor influencing the heating potential of fuelwood. Efficient combustion is greatest in wood that is well dried.

There are many benefits and conveniences associated with fuelwood that make it an optimal fuel choice for rural communities worldwide. In many regions, the most obvious benefit is that wood is free and readily available for individuals to collect. A renewable energy source, fuelwood can be managed in ways that replenish tree stocks and maintain a consistent local supply.

This is a claim that other common domestic fuel types such as kerosene, Liquid Petroleum Gasoline (LPG) and coal cannot easily make. Wood fuel is also a desirable form of household energy because it produces smoke that can serve practical purposes. For example, many households use wood smoke to cure meats while other homes with thatched roofing and siding find smoke a useful mechanism for repelling pests and insects.

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