Biomass gasification for decentralized power generation: The Indian perspective

Abstract

This article attempts to highlight the technical and economical issues related to decentralized power generation in India using biomass gasification. Biomass-based energy has several distinct advantages such as wide availability and uniform distribution that puts it ahead among the renewable energy options for India. The estimated potential of power generation through renewable sources in India is 85 GW with biomass power contributing approximately 20 GW. Especially, in the remote areas and hilly terrains of India, biomass gasification-based power generation offers a highly viable solution for meeting energy demands of small villages and hamlets, which would not only make them independent but will also reduce burden on state electricity boards. This paper reviews various technical options for biomass gasification-based low-, medium- and large-scale power generation. We essentially discuss the merits and demerits (operational and other problems) of different systems. Further, we also deal with economics of these systems and discuss principal factors influencing the viability of the biomass-based power generation. Finally, we review some case studies of biomass-based power generation for meeting energy needs, both thermal and electrical.

Introduction

For a developing country like India, energy is the fundamental input for economic growth. The current target of economy growth rate is 10% and the energy demand in various sectors such as agriculture, industry, transport, commercial and domestic is fast rising. Electricity is perhaps the most vital form of energy input required for infrastructural development of the country in agriculture and industry, and it also plays a critical role in socio-economic development. The total installed capacity of power generation through various sources (as on February 2009) is about 147.72 GW with gross generation of more than 700 billion kWh [1]. The distribution of power generation through different sources, however, is uneven as shown in Fig. 1. The thermal power contribution to this is ∼63% followed by hydropower contributing ∼25%. The share of nuclear power is the smallest with ∼3%, and the power generation through renewable sources contributes the remaining ∼9% [2], [3]. The exact distribution of the power scenario in various states of India is given in Table 1. After grouping of the states into various regions, the distribution of power generation is shown in Fig. 2. The reason behind this uneven distribution is that India has over 200 billions tons of coal deposits. Thus, the generation is mainly dominated by coal-based thermal power plants. However, the coal reserves are mainly concentrated in the north and northeastern states of India and not uniformly spread in the country (refer to Table 2 for distribution of coal deposits in various states). Presently the generation capacity is far insufficient to meet the demands. Although per capita electricity consumption in India during the past 5 years has risen from 566.7 to 704.2 kWh (refer to Fig. 3), it is still far below the global average of 2000 kWh [4]. Currently, the estimated average gap between supply and demand of electricity (peak demand) is about 14%. The transmission and distribution losses are estimated between 26 and 32%. With rapid urbanization and industrialization, this gap is bound to rise fast. In addition, rural electrification has also posed a major challenge to India's growth. The major hurdles in rural electrification are extension of the grid to remote areas, large transmission losses and low peak loads due to small and isolated population [5], [6], [7]. Unlike urban areas, the primary electricity need of the rural population is for domestic lighting, running of irrigation pumps and small-scale commercial activities such as floor mill and other rural industries. The National Electricity Policy (NEP) announced by Government of India along with other activities such as Rajiv Gandhi Grameen Vidyutikaran Yojana has given high priority to rural electrification. The primary aim of this is to achieve complete rural electrification by 2010. Table 3 gives a more detailed account of the status of rural electrification in various states of India. In order to present a realistic picture of rural electrification, Ministry of Power of Government of India has modified the definition of an “electrified village”. Earlier definition of electrified village was “a village in which electricity is being used within its revenue area for any purpose whatsoever”. In 2004–2005, this definition was given four important criteria as follows [8], [9]:

• Provision of basic infrastructure such as distribution transformer and distribution lines in the inhabited locality.

• Provision of electricity to public places like schools, Panchayat offices, health centers, etc.

• Access of electricity to a minimum of 10% households in the village.

• Compulsory certification from Gram Panchayat regarding completion of village electrification.

Although the overall rural electrification stands at an impressive figure of 82%, the actual number of households accessing the electricity is mere 44% [10]. Presently, the rural electrification is growing at a rate of 3–6% annually [9], [11]. In very remote areas where extensive of grid is not feasible, decentralized power generation through renewable sources offers a viable solution for meeting the electricity needs of the local population [12], [13], [14]. In fact, the NEP insists on use of both conventional and renewable sources of electricity generation, as long as they are economically viable. In order to reduce load on grid and state electricity boards, NEP emphasizes use of renewable energy even in areas with access to grid, provided renewable sources are as economic as conventional ones. Options for decentralized generation through renewable sources for are wind energy systems, solar photovoltaics, biomass gasifiers and small hydropower systems, etc. [10]. The most economic option depends on the location of area and natural resources available [15]. Another motive for exploration of renewable sources for power generation is the fluctuating economy of the conventional sources. The principal sources of energy are fossil fuels such as coal, oil and gas. However, the prices of oil and gas are highly fluctuating and there is also a fear of their acute shortage in the future. Moreover, emancipated use of fossil fuels also causes environmental pollution problems such as emission of greenhouse gases. Thus, there is an urgent need for harnessing the large potential of renewable energy sources in a planned and strategic manner to reduce the gap between demand and supply. Promotion of energy conservation and increased use of renewable energy are the twin planks of a sustainable energy supply [14], [16]. In this paper, we have attempted to review the feasibility of the decentralized power generation through biomass gasification and technical and economic aspects related to this. The estimated annual biomass production in India is 200 million tons, which (unlike coal) is distributed almost evenly in the country (greater details about this are given in section 3). This is equivalent of 20 GW of installed capacity. In addition, agro-residues and woody bio-residues from wastelands (estimated at 60 million hectares) could add another 100–300 million tons, which amount to 45 GW of installed capacity. However, the total installed capacity of biomass-based power generation (inclusive of bagasse and non-bagasse cogeneration and biomass gasifiers; as of September 2007) is 838 MW [17]. This capacity is mainly through cogeneration (692.3 MW through bagasse fired boilers), which is an inefficient method of utilization of the biomass energy. This indicates that the vast potential of biomass power remains almost unused, and there is an urgent need of utilization of this resource through more efficient technologies such as biomass gasification.