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

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

* 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

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

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.