Beneath the surface of the earth lies a huge tremendous store of heat called geothermal energy. Much of this heat is stored in underground layers of molten rock, or magma. The earth’s heat is indeed a treasure because it is a clean source of energy that offers distinct advantages over oil, coal, natural gas, and nuclear power.
The temperatures deep inside the earth are in the order of hundreds and even thousands of degrees Fahrenheit. The amount of heat conducted to the earth’s surface from this interior in one year is thought to equal some 100 billion megawatt hours of energy
Tapping Underground Heat
A certain amount of earth’s heat is present in the ground, even near the surface. This can be tapped using heat pumps connected to loops of piping buried in the ground. The energy thus gathered can be used to heat homes in the wintertime or perform other useful work. Moreover, people living near hot springs or other geologically active areas have been able to use the available heat from the earth in additional ways. The ancient Romans, for example, used hot springs for baths.
The greater concentration of heat lies under the earth’s crust, in a layer called the mantle. The average thickness of the crust is about 20 miles [35 km]
Putting the Heat to Work
At sea level, water boils at 212 degrees Fahrenheit [100°C]. But underground, pressures are much higher, and water remains liquid at higher temperatures.Where the drilling taps into water that is above 350 degrees [175°C], the water can be used to drive electrical generators.Water at high temperatures is usually found in areas of recent volcanic activity, such as the Pacific Ring of Fire, a region of both active and dormant volcanoes in the Pacific area.
Pluses and Minuses
There is a lot to be said for geothermal energy. Countries that develop power from it reduce their dependence on oil. Every ten megawatts of electricity generated for a year represents a savings of 140,000 barrels of crude oil per year. Furthermore, geothermal resources are immense, and the danger of depletion is much less than it is with many other energy sources. Pollution problems are also greatly reduced. In addition, geothermal energy production costs are quite low compared with those of many other energy forms.
On the negative side, there are some environmental concerns. Geothermal steam usually contains hydrogen sulfide, which is toxic in high quantities and a nuisance in low quantities because of its sulfurous smell. However, treatment processes for removing it are effective and more efficient than emission-control systems at fossil-fuel power plants. Moreover, particulates in the effluent may contain small amounts of arsenic or other toxic substances. When these are reinjected into the ground, the danger is kept to a minimum. Contamination of groundwater supplies can also be a problem if the geothermal wells have not been sealed to great depths with steel casings and cement.