Since the Arab oil embargo of 1974, it has been clear that the days of almost limitless quantities of low-cost energy have passed. In addition, ever worsening pollution due to fossil fuel consumption, for instance oil and chemical spills, strip mining, sulphur emission and accumulation of solid wastes, has, among other things, led to an increase of as much as 10% in the carbon dioxide content of the atmosphere in this century. This has induced a warming trend through the 'greenhouse effect' which prevents infrared radiation from leaving it. Many people think the average planetary temperatures may rise by 4°C or so by 2050. This is probably true since Antarctic ice cores evidence indicates that, over the last 160000 years, ice ages coincided with reduced levels of carbon dioxide and warmer interglacial episodes with increased levels of the gas in the atmosphere. Consequently, such an elevation of temperature over such a relatively short span of time would have catastrophic results in terms of rising sea level and associated flooding of vast tracts of low-lying lands. Reducing the burning of fossil fuels makes sense on both economic and environmental grounds. One of the most attractive alternatives is geothermal resources, especially in developing countries, for instance in El Salvador where geothermal energy provides about a fifth of total installed electrical power already. In fact, by the middle 1980s, at least 121 geothermal power plants were operating worldwide, most being of the dry steam type.

In many developing countries the exponentially growing electricity demand can be covered by using locally available, sustainable low-enthalpy geothermal resources (80-150 °C). Such low-enthalpy sources can make electricity generation more independent from oil imports or from the over-dependence on hydropower. Until now this huge energy resource has only been used by some developed countries like the USA, Iceland and New Zealand. The reason why low-enthalpy geothermal resources are not used for electricity generation is that there is still a misconception that low-enthalpy thermal fluids are fit only for direct application. The advancement of drilling technology, development of efficient heat exchangers and deployment of high sensitive binary fluids contribute to the useful application of this energy resource on a much wider scale. This book focuses on all aspects of low enthalpy geothermal thermal fluids. It will be an important source book for all scientists working on geothermal energy development. Specifically those involved in research in developing countries rich in such thermal resources, and for agencies involved in bilateral and international cooperation.