ReadingGeothermal energy is natural heat from the interior of the Earth that is converted to heat buildings and generate electricity. The idea of harnessing Earth`s internal heat is not new. As early as 1904, geothermal power was used in Italy. Today, Earth`s natural internal heat is being used to generate electricity in 21 countries, including Russia, Japan, New Zealand, Iceland, Mexico, Ethiopia, Guatemala, El Salvador, the Philippines and the U.S. Total worldwide production is approaching 9000 MW, double of the amount in 1980. Some 40 million people today receive their electricity from geothermal energy at a cost competitive with that of other energy sources. In El Salvador, geothermal energy is supplying 30% of the total electric energy used. However, at the global level, geothermal energy supplies less that 0.15% of the total energy supply.Geothermal energy may be considered a nonrenewable energy source when rates of extraction are greater than rates of natural replenishment. However, geothermal energy had its origins in the natural heat production within Earth, and only a small fraction of the vast total resource base is being utilized today. Although most geothermal energy production involves the tapping of high heat sources, people are also using the low-temperature geothermal energy of groundwater in some applications.The average heat flow from the interior of the Earth is very low, about 0.06 W/m2. This amount is trivial compared with the 177 W/m2 from solar heat at the surface in the U.S. however, in some areas, heat flow is sufficiently high to be useful for producing energy. For the most part, areas of high heat flow are associated with plate tectonic boundaries. Oceanic ridge systems and areas where mountains are being uplifted and volcanic island arcs are forming are areas where this natural heat flow is anonymously high.On the basis of geological criteria, several types of hot geothermal systems have been defined, and the resource base is larger than that of fossil fuels and nuclear energy combined. A common system for energy development is hydrothermal convection, characterized by the circulation of steam and/or hot water that transfers heat from depth to the surface.What is true about geothermal energy production worldwide?