Sad neglect of geothermal energy

Discussions on the merits and demerits of energy resources and their availability are centred on the renewable/non-renewable or conventional/non-conventional energy resources. The prime candidate between non-conventional and renewable energy sources is solar energy, which is projected as a big supplier of our future energy requirements super(1,2), but production of energy is not large so far even today. Once boiling, liquid ball earth cooled to the present condition by gradual loss of heat over billions of years. The hot interior funds the incessant loss of heat from every part of the earth, which flows out unevenly through the surface apparently in small amounts (84 mWm super(-2)), depending upon the geological set-up of the area. The net annual heat loss by this conduction mechanism from the earth is 4 x 10 super(13) W; this is more than the energy released by all earthquakes in a year super(3). On the contrary, nature has geologically controlled but sporadically distributed high-temperature anomalous thermal manifestations with economic potential such as the presence of magma pockets, volcanic eruptions, geysers, fumaroles, solfatara, hot grounds, hot dry rocks, geopressurized water and the highly useful hot-water springs. Springs emitting water more than 5 degree C than the average annual temperature of the area fall under the hot-water category. The water temperature and quantity are controlled by the geological characteristics of the region. Inside the earth water is heated up by magma pockets, cooling crystalline igneous rocks, tectonic activity located within the range of a few hundred metres to a few kilometres depth and by the downward increasing geothermal gradient. This is 30 degree C/km under normal conditions; however, it ranges from as low as 10 degree C/km to exceptionally high values near the mouth of a volcano. The quantity of emitted water is controlled by depth of the heat source, porosity and permeability of the rocks, quantity of percolating meteoric water or source of water, fractures and structural set-up of the area. The geothermal water cycle comprises downward percolation of meteoric water inside the earth through pores and fractures to lateral migration over the heat source and finally emergence of water on the surface. The entire process from percolation to re-emergence of water may be completed in hundreds to ten thousands of years. Once the cycle is established, it may survive up to a million years super(4).