What does this passage discuss mainly

Câu hỏi :

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42. 

     Geothermal energy offers enormous potential for direct, low-temperature applications. Unlike indirect applications, this new technology relies on the Earth's natural thermal energy to heat or cool a house or multifamily dwelling directly without the need to convert steam or other high-temperature fluids into electricity, using expensive equipment. 

     A geothermal system consists of a heat pump and exchanger plus a series of pipes, called a loop, installed below the surface of the ground or submerged in a pond or lake. Fluid circulating in the loop is warmed and carries heat to the home. The heat pump and exchanger use an electrically powered vapor-compression cycle - the same principle employed in a refrigerator - to concentrate the energy and to transfer it. The concentrated geothermal energy is released inside the home at a higher temperature, and fans then distribute the heat to various rooms through a system of air ducts. In summer, the process is reversed: excess heat is drawn from the home, expelled to the loop, and absorbed by the Earth. 

     Geothermal systems are more effective than conventional heat pumps that use the outdoor air as their heat source (on cold days) or heat sink (on warm days) because geothermal systems draw heat from a source whose temperature is more constant than that of air. The temperature of the ground or groundwater a few feet beneath the Earth's surface remains relatively stable – between 45°F and 70°F. In winter, it is much easier to capture heat from the soil at a moderate 50°F than from the atmosphere when the air temperature is below zero. Conversely. in summer, the relatively cool ground absorbs a home's waste heat more readily than the warm outdoor air. 

     The use of geothermal energy through heat-pump technology has almost no adverse environmental consequences and offers several advantages over conventional energy sources. Direct geothermal applications are usually no more disruptive of the surrounding environment than a normal water well. Additionally, while such systems require electricity to concentrate and distribute the energy collected, they actually reduce total energy consumption by one-fourth to two-thirds, depending on the technology used.  For each 1,000 hones with geothermal heat pumps, an electric utility can avoid the installation of 2 to 5 megawatts of generating capacity. Unfortunately, only a modest part of the potential of this use for geothermal energy has been developed because the service industry is small and the price of competing energy sources is low. 

What does this passage discuss mainly?