| Application of biomass-energy technologies |
|VI. Conversion of biomass into electricity|
In India, there has recently been increasing interest in large community-sized digesters, of which around 25 are now in operation nationwide. An example of one of the few successful community biogas plants can be found in Pura village, some 100 miles west of Bangalore. The Centre for Application of Science and Technology to Rural Areas (ASTRA) at the Indian Institute of Science at Bangalore helped to build the community plant. As explained earlier, despite careful planning and execution, the plant was initially subject to many problems. However, ASTRA learnt a lot from this first effort and used the experience and recommendations of the villagers to redesign the plant to meet different requirements (Ready et al, 1990).
As of April 1991, the population of Pura village was 463. Before the biogas system was installed, only 45 per cent of the homes were electrified from the grid (Rajabapaiah et al, 1992), and this often did not provide enough electricity to power their lights.
Although the team from ASTRA had assumed that gas for cooking would be a priority, the villagers of Pura actually put clean drinking water first. It had been calculated that the digester could supply enough gas to power a generator to supply electricity which could then be used to pump water to a reservoir. However, the villagers, understandably, wanted assurance that other people would supply dung before they handed over their own. At the same time, ASTRA wanted the assurance that people would supply dung before it set up the water pump. There seemed no way out of this impasse, and the biogas project stopped in 1984. Meanwhile, other developmental project work by the ASTRA team within the village continued, and it was eventually able to overcome many of the problems and revive the project.
It was possible to set up the biogas plant in the first place because the villagers had nothing to lose by participating in the project. Women already collected the dung for use as fertilizer, the project merely "borrowed" this dung and returned an equivalent quantity of better-quality slurry. However, to make it successful required the establishment of community involvement in the organization and running of the scheme. According to Rajabapaiah et al, (1992),
"The crucial administrative step in Pura was establishing a scheme for dung collection and sludge return based on a delivery fee (of Rs. 0.02 or 0.1586 US cents per kilogram), which goes primarily to the women. This ensures the involvement of women who are the principal beneficiaries of the water supply and the electric lights."
Once villagers experienced the benefits of the gas - clean drinking water from taps, a reliable source of electricity, improved fertilizer etc. - they were willing to take responsibility for the running of the digester, and ensuring that the benefits were distributed fairly. A village development society (grama vikasa sabha) was established involving the traditional community leaders. Pura had not had a village committee since before colonial days. They achieved an outstanding 93-per cent collection of dues from 1988 to 1991. Equity is maintained by keeping records of the weight of dung delivered and compost received for each family. These records are displayed publicly for all to see. The system appears to work well (Hall and Rosillo-Calle, 1991; Rajabapaiah et al, 1992).
The biogas system still consists of two plants with a common inlet tank connected to a dualfuel engine. Between September 1987 and April 1991, the engine ran for about 4521 hours, and an 80 per cent diesel replacement rate was achieved. The project is now managed by the villagers and employs two village youths to operate the biogas plant and the electricity and water distribution systems, while maintaining plant records and accounts. Their salaries are provided by the project sponsor, the Karnataka State Council for Science and Technology (Rajabapaiah et al, 1992).
In September 1987, the water-supply system began operating consisting of a 3 HP pump lifting water from a 50 m depth to an overhead tank from which it is distributed by gravity to nine public taps, the location of which was decided by the villagers. This saved the villagers travelling 1.6 km for water collection and caused an increase in per capita consumption of water, although the villagers have restricted access to the water supply to keep the consumption to a reasonable level. By September 1990, 29 private taps had been installed in households for which the owners pay a tariff. Excess electricity is used to power domestic lights (currently 103 X 20 W fluorescent tubes), for which the recipients also pay (Rajabapaiah et al, 1992).
The economics of production are highlighted in table 11. From September 1990 to April 1991, the revenues from lighting and private water taps covered 93 per cent of the expenditures apart from the workers' salaries. The biogas system is operated for about 4.2 hrs/day with a dung input of 291 kg/day and a unit cost of energy over $US0.25/kWh. However, the system is capable of handling 1250 kg dung/day (the amount of dung actually produced in the village) and operating for 18 hrs/day which would reduce the unit cost considerably. The income from lights and private water taps currently covers only about half of the recurring expenses, but as demand for electricity and supply of dung increases, and costs fall, this will become more economic. When the hours of operation reach 6 hrs/day, at current tariff charges, the system will cover all of its operating expenses and the surplus can be used to return the capital investment. At 15.1 hrs/day, the unit cost of electricity is lower than that from a central power station. Extra gas can be used, for example, for cooking or to provide power for local industries, thereby increasing living standards even further. There are plans under consideration for a dairy development scheme, selling milk and providing more dung.
Rajabapaiah et al, (1992) believe that
"The Pura biogas plant is held together and sustained by the convergence of individual and collective interests and that Non-cooperation with the community biogas plant results in a heavy individual price (access to water and light being cut off by the village), which is too great a personal loss to compensate for the minor advantages of non-cooperation to collective interests."
Residents now realise that biogas has raised their standard of living by making their lives more comfortable at a relatively low cost, so they will ensure that the system is maintained; this is a good illustration of the meaning of sustainable development. One resident is quoted as saying "The grid provides government power, but biogas provides people power, which is far more reliable".
People in Pura village are now thinking of building a wood gasifies to provide producer gas as a supplement to its supply of biogas. Their gasifier would be similar to the successful project in the nearby village of Hosahalli the next case study - which provides electricity for lighting and water pumping. They are establishing an energy forest to grow the feedstock and ASTRA is confident that the villagers will follow it through, having seen a nearby success of a gasification system and the benefits of electrification.