Prof. D.Chandrasekharam, geothermics,hydrogeochemistry,volconology,iitb,india

Nearly 70% of India's power production is based on coal due to the availability of huge coal reserves in the country. Excessive use of this source without the use of strategies to mitigate its effects will have deteriorating effect on the quality of human life. In another decade emission of CO₂ , SO₂ and Nx will exceed 1500 million tones, 1900 kilo tones and 1200 kilo tones respectively (World Bank Report 1999). This means CO₂ emissions will be 775 million metric tones per year as compared to 1000 million metric tones per year produced in the entire European Union! No doubt the cost of electricity produced from coal is far less expensive compared with other fuels. The present day cost of one unit of power is less than a rupee in the case of coal based power while liquid fuel based power costs about Rs. 2 per unit (Mehta, 1999) and hydro power costs about Rs. 1.50 (World Bank Report, 1999). But the expenditure spent to meet the consequences (like disposal of fly ash; treating the coal with high ash content etc) is high which automatically increases one rupee a unit to several rupees. Now a time has come to look into those alternate energy sources which were not viable a decade ago due to non availabilities of technical know how. At present 1.5 percent of total power generation capacity come from non-conventional energy sources like wind, solar and bio -mass. In the next fifteen years, according to the World Bank report (World Bank report, 1999), this energy supply could increase by seven times and above. Below table give the present status of power production from non-conventional energy sources (Chandrasekharam, 2000). Geothermal energy which has a potential of generating about 10,000 MW of power does not figure in the table.

The reasons for low targets achieved in this form of power sector are many. For example, solar photovoltaic (SPV) and solar thermal are far less economically attractive than conventional technologies for the current estimated cost of SPV modules are around $ 4 to 5 Wp(peak watt). Assuming the cost to decline by 50% in future, the estimated cost would be around $2.5 Wp which is highly uncompetitive compared with $ 1.05 for other conventional sources. In the case of wind power, operational problems in matching demand and supply exists since the wind velocity is seasonal (World Bank Report 1999). The estimated cost of power produced using geothermal resources is less than Rs. 2 /kWh (Entingh et al., 1994). Geothermal energy based power production over the world has gone up twice from 5800 MW to 8400 MW with in an year from 1998 to 1999 (Chandrasekharam, 2000). Emission of CO₂, SO₂ by geothermal power plants is far less compared with conventional fossil fuel based power plants. Thus geothermal is quite competitive and eco-friendly and certainly improves the quality of lives in India.

Opportunities for small geothermal power projects exist in many parts in India. Small scale power projects are those with less than 5 MW of capacity. Such small scale power plants can supply electricity in remote areas.

Nearly 400 low to medium enthalpy thermal springs exists in India. These are distributed in seven geothermal provinces. The surface temperatures of these thermal springs vary from 47 to 98^oC. Total power generating capacity of these provinces is estimated to be of the order of 10,000 MW (Ravi Shankar, 1996; Chandrasekharam, 2000). The reservoir temperatures estimated based on water and gas geothermometers vary from 120 to little over 150^oC Minissale et al., 2000). These provinces are the sites for commissioning small scale power projects using binary plant technology (Chandrasekharam, 1999). They are also the best sites for direct application technologies. Direct application technologies are those where the heat energy is utilized directly by a variety of small scale industries. Dehydration of agricultural produce and green house are two such industries to name, which can utilize this energy with maximum profits.

Small geothermal power plants such as binary power plants can be manufactured and can be operated in remote areas depending on the geographic locations of the areas such plants can be modified. Since most of the resources which India has is of medium to low enthalpy in nature, binary power plants are most suited under such situations. The cost of small geothermal power plants depends significantly on power plant costs, drilling costs, resource quality and costs of financing. The expenditure for drilling and developing a geothermal well is "one time expenditure" and further cost for maintaining the equipment is minimum. A comparative costs of power generated by diesel generators and geothermal power is shown below.

An effective, economical exploration programme is essential for successful geothermal projects. When characterizing resources for small geothermal projects, the developer must inexpensively identify resources of sufficient quality in terms of temperature, depth, chemistry to permit a group of economically viable projects. In the case of Indian geothermal provinces, basic data on the chemical signature of the thermal waters and gases associated with the thermal waters, at least on majority of the thermal springs, already exists (Chandrasekharam, 1999, 2000, Minissale et al., 2000 and the references sited therein). An exploration plan for small geothermal plant sites should pool exploration risks across many small projects and identify a group of projects that will be logistically viable when bundled. Small projects cannot afford high drilling costs, such as $ 1-3 million per well spent during exploration for large projects. Drilling slim holes for exploration and production or using smaller more portable drill rigs are promising methods to reduce costs considerably. Conventional production wells have a maximum production zone diameter of 8.5 inches with a 7 inch slotted liner in the production zone (Pierce and Livesay, 1994). Slim hole, on the other hand have a production zone diameter of less than 6 inches. About 40-60% reduction in drilling costs can be achieved using slim hole technology( Finger, 1998).

Access to better energy technology could improve rural people's lives and small geothermal plants could be one of those technologies. Rural electricity services can be improved by installing individual systems, national grids and small mini-grids. In the case of remote areas where supplying power is uneconomical, due to transmission losses and length of transmission line costs, small scale geothermal power projects become handy. With low per-capita electricity demands typical of rural people in our country, this market may best served by many small generating units rather than fewer larger ones. Estimates made on other developing countries (like Latin America, the Caribbean and Philippines) indicate that at 100 watts per house hold (for lighting), 1 MW plant can serve about 10,000 house holds (Cabraal et al., 1996). We have similar situation in the hill states like Himachal Pradesh where small scale power projects are best suited and cost effective.

Electric sector reform is transforming the potential owners and operators of small geothermal projects from public utilities to private power producers. Reform is intended to improve the overall economic efficiency of the electric sector and may open new opportunities for small geothermal projects in this more competitive market. Systems for use of geothermal energy have proven to be extremely reliable and flexible. Binary power plants are on line an average of 97% of the time, whereas nuclear plants average only 65% and coal plants only 75% on-line time. Geothermal plants are modular, and can be installed in increments as needed. Because they are modular, then can be transported conveniently to any site. Both baseline and peaking power can be generated. Construction time can be as little as 6 months for plants in the range 0.5 to 10 MW and as little as 2 years for clusters of plants totaling 250 MW or more. One such binary power plant in operation at Wineagel Developers geothermal site in California, USA, generating 750 kW is shown in below picture. This plant consists of two binary units with a gross efficiency of 8.5% and a capacity factor of 109%. Several such plants exists in China acros s Indian's border, generating 1 MW of power and several such plants are in operation in the world today (Lund and Boyd,1999).

Companies from USA, Europe, Japan, Iceland, New Zealand and developing countries will compete for profitable small geothermal projects in remote areas. If this market develops, the geothermal industry can provide the relevant technologies and experience for successful small projects. With the ongoing reforms in power sector, a large number of independent power producers are entering the power market over the world. Several major types of contractual arrangements for private power producers include (Vimmerstedt, 1998) BOO (Build-Own-Operate), BOT (Build-Operate-Transfer) and BTO (Build-Transfer-Operate).

Small geothermal power projects, less than 5 MW size could improve rural electric supply for the growing markets and improve the socio-economic status of rural India. Binary power plants are technically proven and are being in use in almost all the countries of the world. Exploration for small geothermal projects is inexpensive and the cost of the power produced will be cost competitive. Methods to reducing drilling costs include using slim holes for exploration and production and advanced drilling systems. Rural people have pressing energy needs and electricity from small geothermal plants could meet some of these needs. As electric sector reforms, private power producers become more likely customers from small geothermal power plants than public utilities. International firms from USA, Europe, Japan, Iceland, New Zealand could develop small geothermal power projects. These companies have the appropriate technologies for small projects and have experience in international geothermal projects and development. These industries might respond to a growing small-scale geothermal market by tailoring power plants, drilling rigs, pumps and other equipment to small applications. Better market infrastructure and innovative financing could improve industry success in these markets.