Today, many biomass materials can be used to produce energy and new materials are currently being considered. Biomass fuels are all types of organic materials produced in a renewable manner often coming from industrial activities residues. Three categories of biomass fuels are traditionally considered. Vegetal fuels and animal wastes comprise the vast majority of available biomass fuels while municipal solid waste close the loop. These three categories encompass raw materials such as: forestry products & byproducts, mill residues, agricultural residues, urban wood and yard wastes, biomass crops, chemical recovery fuels, animal wastes, and dry animal manure.
In general, biomass materials tend to have high moisture content. When considering using those for heating, moisture content is central as it decreases combustion performance. It also adds weight and volume which increase transportation costs and make storage harder. That is why biomass fuels have often lower energy density when compared to fossil fuels and it explains why biomass are typically consumed on-site or transported on short distances only.
Wood pellets directly address these central concerns, making wood pellets a unique fuel of its kind. In 
fact, pellets are made from wood that is condensed under heat and pressure. The natural plant components hold the pellets together without glues but natural binders (e.g. starch) could be added to further improve the pellet quality. Pellets commonly used in Europe have less than 10% water content and a uniform density. The energy content of wood pellets is approximately 4.6 – 5.1 MWh/tonne¹. In other words, one ton of wood pellets has the energy equivalency of +/- 500 l of heating oil! When used in high-efficiency wood pellet stoves and boilers, pellets typically offer combustion efficiency of over 85%. There are even condensing pellet boiler offering the best efficiency achievable. Thanks to their excellent energy density, wood pellets are also limiting the cost of transport and storage which make them competitive compared to fossil fuel. Typically, wood pellets are stored in a silo (similar to those housing grain) or other type of tank. Wood pellets can be conveniently stored for years.
These technical assets linked to the availability of its resources explains the great success of the wood pellet, which has gone from a niche product to a well developed energy commodity.
¹ Lower Heating Value as received