Energy 29 (2004) 155–166 www.elsevier.com/locate/energy
Sustainability of decentralized woodfuel-based power plant: an experience in India Sonaton Ghosh a, Tuhin K. Das b, Tushar Jash a, a
b
School of Energy Studies, Jadavpur University, Calcutta 700032, India Department of Economics, School of Energy Studies, Jadavpur University, Calcutta 700032, India Received 22 August 2001
Abstract In accordance with the long-term policy objectives of the government of India for rural electrification, an off-grid woodfuel-based power plant for generation of grid quality electricity has been installed in a remote island of West Bengal. The present study focuses on technical performance of the largest biomass gasifier based power plant in India. Sustainability of such a power plant has been reviewed with respect to diesel replacement, fuelwood supply, cost of electricity generation and pollution load. # 2003 Elsevier Ltd. All rights reserved.
1. Introduction Since the sixth 5-year plan (1980–1985), India has been providing budgetary support for implementation of various renewable energy programmes for meeting ever-increasing energy demand in rural areas. The government of India has proposed to provide electricity by means of solar, biomass, small hydro and wind energy to all the 18 000 remote and inaccessible villages out of total 80 000 presently unelectrified villages and the households therein in a phased manner by the year 2012 [1]. In accordance with long-term objectives, the government of India has given priority to this rural electrification programme using decentralized biomass-based power plants along with other new and renewable energy technologies. Small power plants of different capacities based on this technology have been installed and are operating in different parts of the country. The major emphasis is on electrification of remote villages where geographical location makes it almost economically impossible to extend conventional grid power lines. The
Corresponding author. Tel.: +91-33-473-2853; fax: +91-33-24146853. E-mail address:
[email protected] (T. Jash).
0360-5442/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0360-5442(03)00158-0
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government has been providing capital subsidy (60–100% depending on the plant size and implementing agency) for such programmes. For sustainable wood supply to the wood-fuel based power plant, the government has also initiated dedicated energy plantation programmes. However, almost all such power plants in India biomass fuels are supplied from other sources since the plantation programmes are not yet mature enough to sustain the fuelwood supply at a level necessary for year-round operation of the power plants. Biomass based power plants in India have been generating electricity for the last 6–7 years. Biomass gasifiers have been in use since the late 1980s in the country, but only for thermal applications or for operating irrigation pump sets [2]. Installation of biomass based power plants for generation of grid quality electric power started in the mid-1990s. In these power plants, dual-fuel internal combustion engines run by diesel and gasifier gas are used to rotate the generators. Although the manufacturers of closed-top biomass gasifiers in India are claiming a diesel substitution of over 70% in such power plants, no study appears to have been reported regarding the actual level of diesel substitution in field conditions based on long-term operational data. Mukunda et al. [3] reported a diesel replacement of more than 80% in open-top wood gasifiers. In addition to other factors, substitution of diesel by gasifier gas also depends on load condition. No work has been reported on the dependence of diesel substitution on electrical load in a relatively large power plant. For this reason, it was decided to study the performance of the first commercially run largest biomass gasifier based power plant in India. The objectives of the present investigation were: (1) to monitor the technical performance of the 500 kW biomass power plant at Gosaba in Sunderbans, for a longer period (2 12 years); (2) to study the effect of variation in electrical load on diesel substitution; (3) to study the impact on energy consumption pattern and the consequent rural development, if any, after commissioning of the power plant; (4) to estimate the cost of electricity generation and sustainability of the wood-based power plant; and finally (5) to estimate the environmental pollution load due to the power plant.
2. Gosaba power plant A 500 kW (5 100 kW) biomass gasifier based power plant has been installed and commissioned in Gosaba island of Sundarbans, West Bengal, in July 1997 for electrification of five villages comprising more than 10 000 people. Gosaba island is located at a distance of 115 km from Calcutta and is surrounded by a large number of creeks and rivers. As it was almost impossible to extend conventional grid power line, the island remained unelectrified till the commissioning of the power plant. The Gosaba power plant consists of five 100 kW down draft closed-top gasifiers. Each 100 kW unit is equipped with a water-sprayed gas cooling system, a two-stage gas cleaning system, a blower, a Ruston engine (165 HP) coupled with a 125 kVA alternator and several pump sets (1.5 HP) for circulating water in the gas cooling tower and for removal of ash from the reactor. One vibrator is also employed with each gasifier reactor. The capital cost of the project was IRs.10000000. The total number of consumers was 439 in December 1999 (250 domestic and 189 commercial). An energy plantation, exclusively for the power plant, has been carried out in 75 ha of waste land. But at present, fuelwood is supplied to the plant from the local saw mills. A rural energy co-operative (Gosaba Rural Energy Co-operative Society) has been formed for regular operation of the plant and for revenue collection from the
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consumers. The co-operative now gives power to the domestic consumers at IRs.3.25 per unit and at IRs.3.75 per unit to the commercial consumers. The operation has been restricted to 6 h per day from 4.30 to 10.30 in the evening. 3. Methodology and data sources Data sources were empirical as well as collected from secondary sources. To study the effect of variation in electrical load on diesel substitution experiments were carried out for 30 days during January to March 1998. Electricity generations and per day wood and diesel consumption data were collected from the daily log book of the power plant for 30 months (July 1997 to December 1999). Project details and other techno-economic components were obtained from Gosaba Rural Energy Co-operative Society (GRECS) and West Bengal Renewable Energy Development Agency (WBREDA). A total of 60 consumers (about 15% of the total connections) were selected from the consumers’ list (using systematic random sampling technique) and surveyed through personal interview method to gather the required relevant information. A formatted questionnaire was used to record the primary information. Environmental pollution load per kWh of electricity generation has been estimated stoichiometrically. 4. Performance of the power plant The Gosaba power plant has been in continuous operation since July 1997. Initially 183 connections were made. That number increased by 29% per annum. Total electricity generated during the period July 1997 to December 1999 was 351 798 kWh. Average fuelwood and diesel consumption per kWh of electricity generated were 0.822 kg and 0.135 lt, respectively. The diesel replacement was about 59% of the total requirement if the plant would run by diesel only. Reported performance data of 20 kW wood gasifier-based power plants installed in Hosahali and Hanumanthanagara villages in Karnataka, India, showed a fuelwood consumption of 1.25 kg per unit of electricity generated [4]. Overall efficiency of the Gosaba plant was calculated at 19%. Transmission and distribution loss was nearly 13% and internal consumption was 10% of the total power generated. Table 1 shows the generation, consumption and other performance parameters of the power plant. Mukunda et al. [3] have reported an overall efficiency of 24 to 26% for the 100 kW open-top wood gasifier installed in Port Blair. In the Gosaba power plant, engine lubrication oil needs to be changed and the turbo chargers require cleaning after about 225 h of operation. Water is circulated separately at a flow rate of 2880 lt/h through the gas cooling tower and the ash removal system. In both cases water needs a replacement by fresh water after about 220 h of operation. In the gas cleaning system wood dust filter bed and the cotton filter need to be changed after 48–50 h of operation. 5. Effect of the electrical load on diesel substitution Percent of diesel replacement against different electricity loads for the Gosaba power plant were measured and has been plotted in Fig. 1. From the figure it is observed that substitution of diesel by gasifier gas first increases with the increase in load, reaches maximum at 58% load
289 136
35 180
351 798
270 368
Internal conTotal electricity Total wood sumption, kWh consumption at fuel consumption, kg users’ end, kWh
Total electricity generation, kWh
47 782
Total diesel consumption, litre 69 484
Total diesel saved, litre 13
59
Diesel reTransmission and Distribution placement, % loss, %
19
Overall efficiency of the power plant, %
Table 1 Generation, consumption and performance parameters of Gosaba biomass gasifier power plant for July 1997 to December 1999
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Fig. 1. Diesel replacement against load for the decentralized power plant based on woodfuel.
condition, then decreases at a lower rate. Diesel replacement obtained at the optimum load condition was 64%. Raja et al. [5] obtained maximum diesel replacement at 50% load for a small (3.75 kW) gasifier.
6. Change in energy consumption pattern Electricity supply from this newly installed wood-based power plant motivated households having electricity connection to conserve woodfuel through adoption of improved chulas (IC). It was observed that 25% of the surveyed households had started using ICs for cooking. Statistical analysis of wood fuel consumption per household before and after installation of the woodbased power plant has been given in Table 2. The reason behind this is the purchase of fuelwood from the local market by the power plant—a practice almost non-existent before commissioning of the plant. The local people have become aware of the fact that if substantial amount of fuelwood produced from their homestead lands or collected from the wasteland could be saved then this fuelwood could be sold in the market at a reasonably high price. As the only low cost option available to the rural households to save fuelwood was to install ICs, they had started using this device. Moreover, their fuel preferences had changed in favour of commercial fuels like LPG for cooking. From Table 3, it is clear that with electricity, the per capita, per annum gross energy consumption decreased by 10%, while per capita per annum effective energy consumption increased by 6.7%. This is because of efficient utilization of both commercial and traditional energy sources. So far as electricity consumption is concerned it can be seen from
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Table 2 Per household annual woodfuel consumption for cooking before and after the installation of the wood based power plant Scenario
Before installation of the power plant
After installation of the power plant
Item
IC users
Overall
IC users
Non-IC users
Overall
100
25
75
100
1865.5 2528.1 135.5
1135 665.2 58.6
1779 2972.4 167.1
1643.4 2591.5 157.7
Non-IC users
% of household 0 100 Woodfuel consumption per households, kg/yr Mean 1865.5 SD 2528.1 CV 135.5
Note: S.D., standard deviation; CV, coefficient of variation; IC, improved chulha.
Table 4 that the variability of electricity consumption over the years decreased from 17.7 to 14.3%. Also, from trend analysis it has been calculated that average electricity consumption per household per month was 31.6 kWh. These data may provide input to the planners to optimize plant size.
7. Impact on rural development In general, access to electricity has a positive impact on standard of living since electricity is considered as a basic input of modern life. Thus access to electricity in remote areas like an island can be considered as a boost to the growth of village economy. The growth of commercial establishments, the availability of credit from financial institutions like the nationalized bank, and a rise in employment can be considered as indicators of the impact of the power plant on rural development. According to ‘Business Samiti’, Gosaba, the annual growth rate of commercial establishments has increased from 1.8% in 1995–1996 to 7.2% in 1998–1999. This growth can be explained by the emergence of power-dependent establishments like telephone booths, photocopier shops, X-ray and pathological testing laboratories, medicine shops, hotels, restaurants, etc. Information was collected from the State Bank of India (Gosaba branch), new and old commercial establishments and union of rickshaw peddlers to assess the impact of power plant on employment generation and growth in commercial activities. It was found that before 1996–1997 the loans for self-employment schemes were negligible, but after commissionTable 3 Per capita annual energy consumption for cooking and lighting before and after the installation of the wood-based power plant Before installation of the power plant
After installation of the power plant
Energy consumption
Cooking, kCal
Lighting, kCal Total, kCal
Cooking, kCal
Lighting, kCal
Total, kCal
Gross Effective
1 711 062 213 323
135 199 3394
1 572 650 223 728
89 720 7555
1 662 370 231 284
1 846 261 216 717
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Table 4 Average monthly electricity consumption for a domestic consumer (1997–1999), kWh Year
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean
SD
CV
1997 1998 1999
0 35.5 26.2
0 27.2 28.7
0 34.5 33.0
0 32.7 26.6
0 39.8 28.7
0 22.4 31.5
39.0 26.4 34.75
35.4 32.7 37.2
26.8 36.5 38.2
29.8 36.1 35.4
24.0 33.5 25.1
32.6 26.2 34.9
31.3 32.0 31.7
5.5 5.2 4.5
17.7 16.4 14.3
Note: S.D., standard deviation; CV, coefficient of variation.
ing of the power plant, bank disbursed loans amounted to 1 380 000 Indian rupees under various government sponsored self-employment schemes. The total number of direct and indirect employment has been estimated at 300. This indicates a definite link between employment generation and the operation of the biomass plant. The employment includes trade, transport and operation and maintenance of the power plant. Groscurth et al. [6] also reported that the employment effects of biomass plants was small but positive. In addition, in Gosaba power plant, there would be employment generation of the order of 28 000 man-days during the plantation period [5].
8. Cost of electricity generation The cost of generation of 1 kW-h of electricity from the biomass power plant has been estimated as presented in Table 5. The economics was carried out taking into consideration two scenarios—the reference year and the future year (2012). The cost parameters like load, number of hours of operation per year, capital cost, fuel cost, labour cost, cost of O&M and specific fuel consumption were obtained from actual data provided by WBREDA and GRECS. The life of the power plant and rate of interest on the capital investment has been assumed as 20 years and 6% per annum, respectively. The capital cost includes all the system components of the power plant and the building. Some components may require replacement in less than 20 years’ time which have been assumed to be accommodated within the O&M charges. If the present trend continues, the load on the power plant will be 400 kW in the year 2012 (i.e. 80% of the capacity utilization) and the hours of operation of the plant will have to be increased to at least 12 h per day. The O&M cost has been projected as 1% of the capital cost in the year 2012. The unit cost of generation was 4.27 Indian rupees in the reference year and 4.15 Indian rupees in 2012 exclusive of the capital cost. However, the same was estimated as 9.35 Indian rupees and 4.65 Indian rupees, respectively, when the capital cost was included [7].
9. Sustainability Sustainability of such a power plant has been analyzed with respect to electricity demand, biomass supply and management of the plant. Demand anlysis reveals an increasing demand of electricity overtime in the island as C ¼ ð225:6Þ e0:242t
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Table 5 Economics of electricity generation from the wood-based power plant Cost parameters
Reference year (1999)
Rated capacity (kW) Load (kW) Number of hours per year Capital cost of power plant (IRs) Life time of the plant (years) Cost of wood per ton (IRs) Cost of diesel per litre (IRs) Labour cost per hour (IRs) O&M cost (% of capital cost) Specific wood consumption per kWh (kg) Specific diesel consumption per kWh (litre) Cost of lubricating oil (% of fuel cost) Interest rate (% per annum) Salvage value Cost estimation (IRs)
500 74 2190 10 000 000 20 500 15.39 88 0.08 0.822 0.135 10 6 Nil With capital cost 5.379770 2.737515 1.189189 0.049364 9.355839
Capital cost per kWh Fuel cost per kWh Labour cost per kWh O&M cost per kWh Total cost of electricity generation per kWh
Future year (2012)
500 400 4380 10 000 000 20 1000 20 88 1 0.822 0.135 10 6 Nil Without capital With capital costa cost 0.497629 2.737515 3.874200 1.189189 0.220000 0.049364 0.057078 4.276068 4.648906
Without capital costa 3.874200 0.220000 0.057078 4.151277
1US$ ¼ 47:5 Indian rupees. 0 a The central government and the state government have borne the capital cost as a demonstration project.
where C is the number of electricity connections per month and time t is in years. Thus the annual growth rate of new connections is 29%. It was also revealed from the sample survey that only 48% of the demanded load (including lighting, TV and fan) was met by the power plant. So there was an appreciable gap between demand and supply of electricity. It has been observed that 25% of the surveyed households (domestic) used SPV systems to meet their electricity demand beyond the time schedule. Contingent valuation technique (CVT) has been applied in Gosaba to judge peoples’ sensitivity towards the power plant. People in general agreed to pay an electricity tariff higher than the present rates if supply of electricity was extended beyond 6 h. Households were willing to pay tariff 5 to 20% higher than the present one, while the commercial consumers were ready to pay 10 to 25% higher tariff. This reflects their urge to have uninterrupted electricity supply. For continuous supply of input woodfuel and also to avoid degradation of existing forests, energy plantation in 75 ha of waste land has been done alongwith the setting up of the power plant. At present, woodfuel of the types Acacia arabica Wild, Albizzia blbck Benth and Tamarindus indica of the Leguminoscal family are supplied from local sawmills. High growth species such as Casuarina equisetifolia, Eucalyptus grandis are normally recommended in India for energy plantation. But due to high salinity of the plantation site mangrove species have been planted. The growth of mangrove trees are lower (6 t/ha/year) than the growth rate of the suggested energy plantation (30 t/ha/year) [5]. Based on the gasifier performance data, electricity
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Table 6 Electricity generation, and woodfuel supply under different scenarios Item
Reference
Scenario 1
Scenario 2
Year
1999
2003a
2012
2003
2012
Hours of electricity supply Annual electricity consumption (kWh) Annual electricity generation (kWh) Annual woodfuel consumption (kg) Annual diesel consumption (litre) Annual wood growth from energy plantation (kg) Annual deficit/surplus of wood for electricity generation from energy plantation (kg) Average load (kW)
6 133 708
6 436 342
6 479 976b
12 610 879c
12 671 967b
161 405
566 676
623 345
793 349
872 684
134 316
471 474
518 623
660 066
726 073
21 747
76 501
84 151
107 102
117 850
450 000
450 000
450 000
450 000
450 000
(+) 315 684
() 21 474
() 68 623
() 210 066
() 276 073
74
259
284
362
398
Note: (+) Indicates surplus and () indicates deficit. 0 a 100% connection will be completed at an annual growth rate of 29%. b 10% increase in electricity consumption is assumed due to induced demand. c 40% increase in electricity demand is assumed for additional 6 h during daytime.
generation and wood requirement of the Gosaba plant have been estimated and presented in Table 6. It is evident from the table that in scenario 1, the demand for wood will exceed the supply of wood, if the supply is restricted to that from dedicated energy plantation only. This deficit will increase further if the electricity consumption increases either due to induced demand or increased hours of electricity supply or both. Now the third aspect, i.e. participation of the local people in the management of the plant, is considered as an important component for sustainability of the decentralized power plant. GRECS is functioning efficiently in managing operation and maintenance of the Gosaba plant. This can be considered as one of the positive steps towards sustainability of the project.
10. Environmental pollution load Total annual emissions of atmospheric pollutants like CO2 and oxides of sulphur and nitrogen from the Gosaba plant have been estimated and summarized in Table 7. In estimating the NO2 emission, only the fuel NOx has been considered. Table 7 reveals that the power plant emits 1743 g of CO2, 1.6 g of SO2 and 3.4 g of NO2 per kWh of electricity generation. However, the present pollution load due to CO2 is neutralized by the energy plantation of the 75 ha undertaken exclusively for the power plant [8]. But the SO2 and NO2 emitted by the plant will increase the pollution load both locally and globally. Moreover, CO2 will also contribute as an
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Table 7 Estimated annual emission of pollutants from the wood gasification based power plant Pollution load CO2 emission from Total CO2 emission
Emission, kg % Emission/ kWh, kg
wood
diesel
222211 79 1.3767
59069 21 0.3659
281280 100 1.7427
SO2 emission from Total SO2 emission
NO2 emission from
wood
diesel
wood
diesel
72 28 0.0004
186 72 0.0012
488 89 0.0030
61 11 0.0004
258 100 0.0016
Total NO2 emission 549 100 0.0034
additional greenhouse gas when increase in power generation occurs in scenario 1 and 2 (Table 6). It can be recommended from Fig. 1 and Table 7 that the electrical load should be managed in such a way that maximum diesel replacement occurs and this will help in reducing the SO2 emission. Besides air pollutants, biomass gasifiers also produce liquid and solid waste. In Gosaba plant, at present, waste water is discharged into an open pond without any treatment. As the waste water contains large amounts of organics it is degrading the adjacent agricultural lands. The ash generated by the power plant is sold to the local incense stick manufacturers which shows that the ash contains considerable amount of unburnt fixed carbon. In a down-draft gasifier, fixed carbon of the biomass fuel remains unburnt and is removed with the ash, if (1) the gasifier is operated at an equivalence ratio which is lower than the prescribed range of 0.25 to 0.30 [9], and (2) sufficient retention time is not provided to convert the solid fuel into producer gas. This is one of the causes for low replacement of diesel and also low overall efficiency of the Gosaba power plant. 11. Conclusions (1) Though the Gosaba biomass power plant has been generating electricity since July 1997, the performance analysis of the plant revealed moderate success of the project with respect to diesel replacement (59%). (2) Electrical load on generator has a strong influence on replacement of diesel by biomass gasifier gas. In the Gosaba 500 kW power plant, maximum diesel replacement obtained at optimum load condition was 64% which is lower than the values reported in the literature [10], and also as claimed by the manufacturers [11]. (3) After commissioning of the power plant per capita gross energy consumption in the island decreased (10%), while the per capita useful energy consumption increased by 6.7%. A large number of households started using improved wood stoves, which were not popular here before 1997. Although the government of India launched the National Programme on Improved Chulha (NPIC) as early as 1983, it recorded little success [12,13] especially in the villages which are in close proximity to natural forests (like Gosaba island in Sundarbans). The study reveals that the reason behind people opting for ICs is purely economic, that is, to sell the fuelwood saved through ICs in the fuelwood market created after commissioning of the power plant. (4) Due to the biomass power plant, commercial activities in Gosaba have increased and the employment generated is small but positive. (5) Unit cost of electricity generation for the reference year has been estimated at IRs 4.27,
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which is higher than the present tariff. As the state nodal agency (WBREDA) has been providing the salaries of the operators and the labourers, the plant at present is operating on no-profit, no-loss basis. To sustain the operation of the power project and also to make it commercially viable, either to higher electricity tariff (to at least IRs 5/kWh) or increased hours of operation or both can be recommended. It is better to fulfill the second option immediately and then to increase the tariff in stages. (6) Thirteen percent T&D loss is quite high for a small, decentralized power plant operating in a relatively closed network. Care should be taken on this aspect in planning such a power plant. (7) At present, the power plant is self-sufficient so far as woodfuel requirement (if it is assumed that 75 ha of plantation will have matured within 2 years) and local management are concerned. But there will be shortage of fuelwood if both electricity demand and hours of operation increase in future. There then arises the question of sustainability of such wood-based power plant. Under such circumstances the best option is more energy plantation and for this planners should consider two aspects—availability of land and the soil condition of the region. There are large areas of foreshore land on the river banks of Sundarbans, and the area in the Indian part of Sundarbans has been estimated to be 0.15 million hectare of which 50 000 ha is suitable for plantation [14]. Thus extensive energy plantation is possible to sustain the wood-based power plant. As the soil is highly saline only mangrove plantation should be undertaken. (8) The fresh water demand and the amount of contaminated water discharged by the power plant are both quite high. To overcome the problem, either the wet cooling systems should be replaced by dry cooling systems (e.g. through large-area metal surfaces) or an effluent treatment plant should be installed within the plant site. (9) The time between change of fresh wood dust and cotton filter in the gas cleaning systems and engine overhaul do not coincide which will pose a serious problem in increasing the hours of operation of the power plant in future. (10) About 75% of the SO2 emitted by the power plant comes from diesel (Table 7). Two technological options for reducing SO2 emission are available: (a) use of boilers and steam turbines instead of burning gasifier gas in dual fuel internal combustion engines; (b) use of 100% producer gas engines for electricity generation. The first option will also reduce the NOx emission as NOx emission (thermal NOx) strongly depends on the conversion technology [6]. However, engines may be the only economically viable option for decentralized power generation in isolated areas with low electricity demand. The solution thus lies in the introduction of 100% gasifier gas-based IC engines. References [1] Ministry of Non-conventional Energy Sources. Annual Report, 1997–98. Block No. 14, C.G.O. Complex, Lodi Road, New Delhi-3, Government of India, 1998. [2] Raman P, Dhingra S, Munda S, Kishore VVN. Development of a biomass gasifier-based power plant for rural electricity. Asian Energy Update 1998;1(1):15–8. [3] Mukunda HS, Dasppa S, Shrinivasa U. Open-top wood gasifier. In: Johanson TB et al., editors. Renewable energy—sources for fuels and electricity. California: Island Press; 1993. p. 699–728. [4] Ravindranath NH, Rao KU, Natarajan B, Monga P. Renewable energy and environment. New Delhi: Tata McGraw-Hill Publishing Company Limited; 2000. [5] Raja B, Narasimhan V, Murugan M, Thirumurugan G, Haridasan TM. Performance study of jetropha oil in the place of diesel in biomass gasifier. In: Maheshwari RC, Chaturvedi P, editors. Bio-energy for rural energisation. New Delhi: Concept Publishing Company; 1997. p. 109–114.
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