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close this bookRenewable Energy Options for Decentralized Electricity Generation - Encology - Vol. 11, No. 2, July 1996 (Centre for Ecological Sciences, INDIA, 1996, 6 p.)
close this folderDecentralized Electricity Generation Options
View the document(introduction...)
View the document1. Solar Photovoltaic Power Systems
View the document2. Micro Hydel Power Systems
View the document3. Wind power generation
View the document4. Biogas based electricity generation system
View the document5. Woodgasifier based decentralized electricity system

4. Biogas based electricity generation system

India has a large domestic animal (cattle, sheep and goats) population. The biogas potential is extremely high. For example in Karnataka the dung available per day during peak (7 months) and lean (5 months) season is 0.109 million tonnes and 0.052 million tonnes respectively. With a dung yield of 3.5 kg/cattle/day during lean season and 7.3 kg/cattle/day during peak season and 35 litres of biogas/kg of dung, the total biogas potential available during lean and peak season is 3.8 and 1.8 m3/day respectively. Taking 0.57 m3 of biogas/kWh of electricity, total potential for electricity generation is 6.6 m kWh/day and 3.16 m kWh/day during peak and lean season respectively. In Karnataka 61% of rural households own cattle and every village has significant cattle population. Thus there is potential for electricity generation in every village through biogas route. However, biogas has another attractive alternate use as fuel for cooking. Use of biogas for cooking saves large amount of fuelwood resulting in slowing down of deforestation rate. It also reduces drudgery associated with cooking considerably.

The decentralized electricity generation system by a community biogas plant is tried out in 1987 in Pura village, Kunigal taluk, Tumkur district of Karnataka State to replace the traditional system of obtaining water, for illumination and fertilizer (for the fields). Improved wood stoves (called ASTRA ole) are being used for cooking which saves fuelwood significantly. Because of multiple advantages affecting directly the rural life like better and cheaper electric illumination than kerosene lamps, better and less effort to get improved water and better fertiliser in the form of sludge, and control of weeds in farms due to high Nitrogen content in the sludge, the biogas system is accepted and maintained by villagers themselves. At Pura village 5 kW electric generation unit using biogas - diesel engine - genset system caters the needs of pumping domestic water and partial lighting. The skill upgradation and training is provided to the two village youths in the operation and maintenance of biogas system. This decentralized system has provided challenging jobs for these two youths. A dung delivery fee is paid to those who deliver the dung to the plant and take back the sludge. Also, this system provides revenue for the village to the extent that the total payment received for the system outputs delivered inside the houses exceeds the expenses for diesel and dung delivery charges. Because of all these a distinct improvement in the quality of life of villagers is noticed especially with regard to health due to safer water and better illumination facilities.

Fig. 1. Unit Cost of Biogas Electricity Effect of Capacity @ 12%

Reddy and Balachandra (1991) have carried out a detailed economic analysis of the community biogas plant electricity generating system based on Pura village data, based on the total life cycle costing method. The cost of electricity at the present rate of capacity utilization (of 4.3 hours/day) is Rs. 2.75/kWh. It can be observed from Figure 1 that as the capacity utilization increases to 15 hours/day the cost/kWh is about half of that. This is comparable with cost figures of centralized systems. Unlike centralized power generation plants, a substantial percentage of the expenditure are incurred locally. The system inturn stimulates local prosperity. The authors have also compared the decentralized biogas system with that of a nuclear power plant. The findings show that in capital starved situations where the real discount rates are high, the cost/kW of installed capacity is lower for biogas system compared to nuclear power plants. Thus it is necessary to explore the biogas option for electricity generation. Infact recent development of usage of cellulose materials like tree leaves, weeds etc as feed stock in biogas plant has boosted biogas potential for power generation.