Though biomass conversion technologics and devices cover a very wide spectrum, these can be covered generally through four major categories :

* Anacrobic Digestion.

* Pyrolysis

* Combustion and

* Gasification

Anaerobic Digestion: Under this process anacrobic baeteria break down the biomass and yield in the proccess a fuel gas consisting about 60% methane and the rest mainly carbon dioxide. This gas, often called 'Biogas' has reasonably good qualities for cooking or for running internal combustion engines.

Pyrolysis can be defined as thermal decomposition of organic matter under vacuam or inert atmospheric condition. Pyrolysis could be largely used for production of various gascous, liquid and solid fuels from biomass, with the most common example being conventional charcoal making.

Biomass combustion can be said to be one of the oldest technologies known by mankind beginning with the first fires built by man. Industrial revolution was largely based on combustion and biomass combustion has been widely practicised all over the world for producing heat as also for generation of shaft power/electricity.

Biomass gasification is basically conversion of solid biomass into a combustible gas mixure normally called 'Produccer gas' which is a low Btu gas. The process is typically used for 'woody' biomass and it involves partial combustion of such biomass. Partial combustion process when air supply is less than adequate for combustion of biomass to be completed. Partial combustion produces carbon monoxide as well as hydrogen which are both combustible gas. This gas can be directly fed into internal combustion engine for production of electricity. Based on this principle a 500 kw capacity gasifier has been installed in Gosaba island of Sunderbans, West Bengal for electrification of five villages comprising of more than ten thousand people.

Gosaba Island is one of the important islands of Sunderbans. It is located in south 24 parganas district. The island is approximately ata distance of 115 km from Calcutta. Till June 1997 Gosaba island was not having any electricity. The entire area used to become dark after sunset. The local people approached West Bengal Renewable Energy Development Agency in the year 1996 for providing of electricity from renewable sources of energy. This is in view of the fact that conventional energy will never come to Gosaba island after crossing of large number of creeks and rivers. After a careful survey of the area WBREDA decided to set up a 500 kw gasifier based power plant at Gosaba Island along with energy plantation in 100 ha of waste land and formation of a rural energy cooperative for regular operation of the power plant.

A proposal was prepared with the following compoents.

* Plant and machinery including control panel.

* Distribution line including sub-station.

The total cost of the proposal was 92.0 lacs. The proposal was approved by both MNES, Govt. of India and the State Govt. The work was taken up in hand in the month of August 96. The plant was completed in all respect by May 97 and put to load in June 97 with only 19 nos consumers and 16 kw load. This is because the people of the island did not have the confidence on the project. However, within a short time number of consumers went up to 177 and many other people started coming to the power plant for getting electricity. Further connection could not be given for want of distribution line. Subsequently, distribution line was extended with the financial help form Zilla Parishad and electric connection was provided to 300 more consumers. Initially the generation cost was almost Rs. 5.00 per unit and now it has come down to Rs. 2.50 per unit. The co-operation now gives power to the consumers at Rs. 3.50 per unit to the domestic consumer and at a rate of Rs. 3.75 per unit to the commercial consumer. Ultimately the cooperation will provide power to about 800 consumers. Attempts are being taken to extend the distribution line and provide connection to more consumers. With 800 consumers the cost of generation will come down to Rs. 2.00 per unit.

Capacity of the power plant 5*100 kw.

Location of the plant Gosaba island

Distance from Calcutta 115 km.

Distance of the grid line 39 km

Up to date expenditure Rs. 95.00 lacs (app)

No of consumers 511.com-157,dom-350,ind-4

Tarriff structure Rs. 3.50/unit for domestic

Rs. 3.75/unit for commerical

Rs. 4.00/unit for industrial

Length of distribution line 11kw line-4 km. LT line-7km

Hours of operation 6 hrs.

Consumption of diesel 0.13 its per unit at 80% load

Consumtion of biomass 900 gms per unit if dried

Operational manpower 10 nos.

Monthly expenditure Rs. 45000.00 (Oct. 98)

Monthly revenue Rs. 46000.00 (Oct.98)

Area under plantation About 100 ha

Expected yield About 10 MT/ha/year.

Indirect employment About 84 heads for Biomass

Generation and supply

Benificiary (Direct & Indirect) 11000

In addition to supply of power to the domestic and commercial consumer the plant is likely to supply 15 kw of power to a water supply scheme coming up in the Gosaba Island.