An aspect that is quite attractive in biomass utilization is its renewability that ultimately guarantees nondepletion of the resource. Considering all plants and plant-derived materials, all energy is originally captured, trans­formed, and stored via a natural process of photosynthesis. Strictly following the aforementioned definitions of biomass, it can be safely said that energy from biomass has been exploited by humans for a very long time in all geo­graphical regions of the world. The combustion, or incineration, of biological substances such as woody materials and plant oils has long been exploited to provide warmth, illumination, and energy for cooking. It has been estimated that, in the late 1700s, approximately two-thirds of the volume of wood removed from the American forest was for energy generation [3]. Because wood was one of the only renewable energy sources readily exploitable at the time, its use continued to grow until the mid-to-late 1800s, when petro­leum was discovered and town gas infrastructure based on coal gasification was introduced. It was reported that during the 1800s, single households consumed an average of 70 to 145 m3 of wood annually for heating and cooking [7, 8]. A small percentage of rural communities in the United States still use biomass for these purposes. Countries including Finland use the direct combustion of wood for a nontrivial percentage of their total energy consumption [9]. Furthermore, Finland has spent significant R&D efforts in biomass utilization programs and has successfully developed a number of advanced biomass conversion technologies. Finland and the United States are not the only countries that use biomass consumption for supplementing their total energy usage. In fact, the percentage of biomass energy of the total energy consumption for a country is far greater in African nations and many other developing countries.

An assessment by the World Energy Council (WEC) [10] reported that the 1990 biomass usage in all forms accounted for 1,070 MTOE, which is approxi­mately 12% of global energy consumption of 8,811 MTOE assessed for the same year. MTOE stands for metric tonnes of oil equivalent. In 2010, about 16% of global energy consumption came from renewables, of which about 10% was contributed from traditional biomass, which was mainly used for heating, 3.4% from hydroelectricity, and 2.8% from so-called "new renew­ables" which included small hydro, modern biomass, wind, solar, geother­mal, and biofuels [11]. The last category of new renewables has been growing very rapidly based on the development of advanced technologies as well as the global fear of depletion of conventional petroleum fuel.

On a larger scale, biomass is currently the primary fuel in the residential sector in many developing countries. Their biomass resources may be in the form of wood, charcoal, crop waste, or animal waste. For these countries, the most critical function of biomass fuel is for cooking, with the other principal uses being lighting and heating. The dependence on biomass for the critical energy supply for these countries is generally decreasing, whereas that for industrialized countries is more strategically targeted for new generation bio­mass energy. According to REN21 [11], the top five nations in terms of exist­ing biomass power capacity in 2011 are the United States, Brazil, Germany, China, and Sweden in order of one to five. The top two nations of this list are also the top two nations in bioethanol production, not coincidentally. In other words, the biomass power category has so far been propelled and dominated mostly by the bioethanol transportation fuel sector.