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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

(introduction...)

The following options could be considered for electricity generation at decentralized level.

1. Solar photovoltaic systems
2. Small hydroelectric plants
3. Wind energy systems
4. Biogas driven gensets
5. Woodgas driven gensets

1. Solar Photovoltaic Power Systems

Solar photovoltaic systems play a vital role on economic growth of a region in relation to power availability and generation capacities because of the following:

(a) pollution free generation
(b) easy maintenance
(c) modular upgradation
(d) decentralized availability
(e) reduction in distribution costs

Though the photovoltaic systems are available they are expensive at present. Also they alone cannot successfully cater to the energy requirements without a very high efficiency balance of system design. The choice of balance of equipments is to be made carefully. Another major requirement is the storage of energy where in batteries of low maintenance and high recycling capacities must be used. Anup Kumar and Vaidehi (1991) compared a photovoltaic system with grid electricity system for village applications. They concluded that photovoltaic power plants are economically viable for providing electricity to villages situated at a distance of 10 kms or more from conventional grid supply lines. In most states such a situation does not exist. Thus photovoltaic power stations are not feasible at the moment though unlimited potential exists for the future.

2. Micro Hydel Power Systems

It is ideally suited to decentralized generation of power for use by disposed rural communities and lends itself to operation and management by the user groups. It is quite, does not pollute the atmosphere or contribute to the green house effect and operates with effectively zero fuel costs.

Micro hydel power systems have potential in some locations with perennial water flow. Some such locations have been identified in several states. Soundaranayagam (1991) has given a cost figure of Rs. 37,000/kW of installed capacity for a prototype demonstration unit of 15 kW capacity.

Small hydro does have its problems, largely associated with non uniform availability of water over a yearly period in small rivers and streams and in the utilisation pattern of small rural communities. An ideal solution to go in for peaking power plants with minimum storage which utilise rainwater during monsoon and can be supplemented by biomass based thermal power plants. Some of the problems, of micro hydel plants are

(a) cost/kW is still high
(b) very few perennial water sources
(c) technical and operational feasibility in the field is yet to be demonstrated.

3. Wind power generation

India has a large wind energy potential. According to one estimate wind potential in India is about 25,000 MW. Attempts are being made to generate electricity through wind farms in several states. In Tamilnadu the installed capacity is 1.1 MW. The overhead costs are high for small capacity systems. Rao (1991) has given the cost of power generation from two wind farms in Gujarat as Rs. 1.36/kWh. Thus wind energy systems are increasingly becoming feasible especially for locations with good wind potential.

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.

5. Woodgasifier based decentralized electricity system

Hosahalli, a backward and non electrified village in Tumkur district (100 kms from Bangalore) with a population of 267 is electrified by a decentralized electricity generation system using a 5 kW (Figure 2) wood gasifier (Ravindranath et. al., 1991). There are 43 houses in this village. Irrespective of social and economic status all 43 houses are provided with two lighting points each (1×40 w fluorescent tube +1+15 w bulb), in addition to street lights. The total lighting load is 2.685 kW. An energy forest has been raised in the community land of 2 ha to supply wood in a sustainable way. Annual productivity of 6 t/ha. has been obtained from this forest (Table 1). The species composition and density of the energy forest are as follows:

Table 1: Productivity of the energy forest

Total productivity dry t/ha

Productivity dry t/ha/yr

At 12 months

696

6.96

At 24 months

12.90

6.45

Coppice yield between 12 and 24 months

-

4.50

Table 2: Operation cost of the woodgas based electricity generation system

Inputs

Qty/kwh

Cost/kwh

Cost/month (Rs.)

Diesel

130 ml

0.52

167

Labour for wood preparation and operation*

0.37 hr

0.70

225

Total

-

1.22

392

* Even though 4 man hours are adequate for the operation of the system, currently more labour is employed in the field as the second phase of the project is still being implemented.

Table 3: Capital cost of 3.7 kw woodgas based and diesel system

Woodgas system

Diesel system

Gasifier

16,000

-

Engine + Gen set

28,600

28,600

Voltage stabilizer + accessories

6,000

6,000

Wood cutter

3,000

-

Building

5,000

5,000

Energy Forest

5,000

-

Total

63,6000

39,600

Life of the gasifier and engine is taken to be 50,000 hours and 20,000 hours respectively. The diesel engine has to be overhauled every 5000 hours. Annual maintenance cost is taken as 5% and 10% for the gasifier and engine respectively at an operational level of 20 hours/day.


Fig. 2: Wood-Gasifier system

1.

Leucaena leucocephala

:

2023

2.

Dalbergia sisso

:

1357

3.

Eucalyptus hybrid

:

1147

4.

Cassia siamea

:

679

5.

Acacia auriculiformis

:

580

6.

Casuarina equisetifolia

:

814

Total trees per ha.

:

6600

The annual wood fuel requirement for the gasifier is 5.1 t at the rate of 1.2 kg of wood/kWh for 4 to 5 hours/day. Thus one ha. of land is adequate to provide wood in a sustainable way for 5 kW system for lighting purpose. Diesel substitution achieved in the field is in the range of 66.9% and 76.8%. The use of electricity for lighting has saved 0.803 t of Kerosene/year in the village. This system is in operation at Hosahalli since 1988. Two trained village boys are operating the system for 4 to 5 hours/day. This endeavour has demonstrated electricity generation system based on a renewable source of energy has been accepted by the village community.

Woodgas system to be replicable must be economically viable. The operational cost and capital cost of the system is given in Tables 2 and 3 respectively. Economic analysis was carried out using the discounted cash flow technique namely net present value (NPV) method. The total life cycle costs and total life cycle benefits were estimated. The results showed that at the current levels of operation of 4 hours/day the woodgas system would be economical only if electricity is priced at Rs. 3.5/kWh. However as can be observed from Figure 3 the cost/kWh decreased to Rs. 2.5/kWh when the hours of operation is increased to 20 hours/day. When compared with a diesel system of similar capacity it can be observed that beyond 5 hours of operation per day the cost/kWh is significantly lower for woodgas system compared to pure diesel system.


Fig. 3: Price of electricity at different hours of operation

Recently, the woodgas system has been diversified to pump water for domestic consumption. It is proposed to operate a flour mill connected to the woodgas system. Thus all the lighting and shaft power needs of the village could be met.