Biomass materials are used since millennia for meeting myriad human needs including energy. Main sources of biomass energy are trees, crops and animal waste. Until the middle of 19th century, biomass dominated the global energy supply with a seventy percent share (Grubler and Nakicenovic, 1988). Among the biomass energy sources, wood fuels are the most prominent. With rapid increase in fossil fuel use, the share of biomass in total energy declined steadily through substitution by coal in the nineteenth century and later by refined oil and gas during the twentieth century. Despite its declining share in energy, global consumption of wood energy has continued to grow. During 1974 to 1994, global wood consumption for energy grew annually by over 2 percent rate (Figure 1). Presently, the biomass sources contribute 14% of global energy and 38% of energy in developing countries (Woods and Hall, 1994). Globally, the energy content of biomass residues in agriculture based industries annually is estimated at 56 exajoules, nearly a quarter of global primary energy use of 230 exajoules (WEC, 1994). 

ADVANCEMENTS IN BIOMASS ENERGY TECHNOLOGIES

Technological advancement in biomass energy is derived from two spheres - biomass energy production practices and energy conversion technologies. A rich experience of managing commercial energy plantations in varied climatic conditions has emerged during the past two decades (Hall et al, 1993). Improvements in soil preparation, planting, cultivation methods, species matching, bio-genetics and pest, disease and fire control have led to enhanced yields. Development of improved harvesting and post harvesting technologies have also contributed to reduction in production cost of biomass energy. Technological advancements in biomass energy conversion comes from three sources - enhanced efficiency of biomass energy conversion technologies, improved fuel processing technologies and enhanced efficiency of end-use technologies. Versatility of modern biomass technologies to use variety of biomass feedstock has enhanced the supply potential. Small economic size and co-firing with other fuels has also opened up additional application.

For electricity generation, two most competitive technologies are direct combustion and gasification. Typical plant sizes at present range from 0.1 to 50 MW. Co-generation applications are very efficient and economical. Fluidized bed combustion (FBC) are efficient and flexible in accepting varied types of fuels. Gasifiers first convert solid biomass into gaseous fuels which is then used through a steam cycle or directly through gas turbine/engine. Gas turbines are commercially available in sizes ranging from 20 to 50 MW. Technology development indicates that a 40 MW combined cycle gasification plant with efficiency of 42 percent is feasible at a capital cost of 1.7 million US dollars with electricity generation cots of 4 cents/ KWh (Frisch, 1993).

Biomass contributes over a third of primary energy in India. Biomass fuels are predominantly used in rural households for cooking and water heating, as well as by traditional and artisan industries. Biomass delivers most energy for the domestic use (rural - 90% and urban - 40%) in India (NCAER, 1992). Wood fuels contribute 56 percent of total biomass energy (Sinha et. al, 1994). Consumption of wood has grown annually at 2 percent rate over past two decades (FAO, 1981; FAO, 1986; FAO, 1996).

Problems of Traditional Biomass Energy Use

Most biomass energy in India is derived from owned sources like farm trees or cattle, or is collected by households from common property lands. The biomass energy consumption is primarily limited to meet cooking needs of households and traditional industries and services in rural areas. In absence of a developed energy market in rural areas, most biomass fuels are not traded nor do they compete with commercial energy resources. In developing countries, due to excess labour, biomass acquires no resource value so long as it is not scarce. In the absence of an energy market, the traditional biomass fails to acquire exchange value in substitution. Absence of market thus acts as a barrier to the penetration of efficient and clean energy resources and technologies.