Applications of Wind Power:
Geothermal power (from the Greek roots geo, meaning earth, and thermos, meaning heat) is power extracted from heat stored in the earth. This geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for space heating and bathing since ancient roman times, but is now better known for generating electricity. About 10 GW of geothermal electric capacity is installed around the world as of 2007, generating 0.3% of global electricity demand. An additional 28 GW of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.
Geothermal power is cost effective, reliable, and environmentally friendly, but has previously been geographically limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for direct applications such as home heating. Geothermal wells tend to release greenhouse gases trapped deep within the earth, but these emissions are much lower than those of conventional fossil fuels. As a result, this technology has the potential to help mitigate global warming if widely deployed.
A lava fountain is an example of the amount of heat stored in the earth.
Direct Applications:
Hot springs have been used for bathing at least since paleolithic times. The oldest known spa is a stone pool on Lisan mountain built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. In the first century AD, Romans conquered Aquae Sulis and used the hot springs there to feed public baths and underfloor heating. The admission fees for these baths probably represents the first commercial use of geothermal power. The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy.
In 1892, the world's first district heating system in Boise, Idaho was powered directly by geothermal energy, and was soon copied in Klamath Falls, Oregon in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland at about the same time. Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from geysers were used to heat homes in Iceland starting in 1943.
The 20th century saw the rise of electricity, and geothermal power was immediately seen as a possible generating source. Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the same Larderello dry steam field where geothermal acid extraction began. It was a small generator that lit four light bulbs. Later, in 1911, the world's first geothermal power plant was built there. It was the world's only industrial producer of geothermal electricity until 1958, when New Zealand built a plant of its own.
At this point, the heat pump had long ago been invented by Lord Kelvin in 1852, and the idea of using it to draw heat from the ground had been patented in Switzerland in 1912. But it was not until 1940's that the idea was successfully implemented. The first commercial geothermal heat pump was designed by J.D. Krocker to heat the Commonwealth Building (Portland, Oregon) in 1946, and Professor Carl Nielsen of Ohio State University built the first residential heat pump two years later. The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The development of polybutylene pipe in 1979 greatly augmented its economic viability. As of 2004, there are over a million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity. Each year, about 80,000 units are installed in the USA and 27,000 in Sweden.
The binary cycle power plant was first demonstrated in 1967 in Russia and later introduced to the USA in 1981.[22] This technology allows the use of much lower temperature geothermal fields that were previously unrecoverable. In 2006, a binary cycle plant in Chena Hot Springs, Alaska, came on-line, producing electricity from a record low geothermal fluid temperature of 57°C.
Electrical Generation:
Twenty-four countries generated a total of 56,786 GWh (204 PJ) of electricity from geothermal power in 2005, accounting for 0.3% of worldwide electricity consumption. This output is growing by 3% annually, thanks to a growing number of plants as well as improvements in their capacity factors. Because a geothermal power station does not rely on transient sources of energy, unlike, for example, wind turbines or solar panels, its capacity factor can be quite large; up to 90% has been demonstrated. Their global average was 73% in 2005. The global capacity was 10 GW in 2007.
The thermal efficiency of geothermal electric plants is low because geothermal fluids are at a low temperature compared to steam from boilers. By the laws of thermodynamics this low temperature limits the efficiency of heat engines in extracting useful energy during the generation of electricity. Exhaust heat is wasted, unless it can be used directly and locally, for example in greenhouses, timber mills, and district heating. The efficiency of the system does not affect operational costs as it would for a coal or other fossil fuel plant, but it does factor into the viability of the plant. In order to produce more energy than the pumps consume, electricity generation requires high temperature geothermal fields and specialized heat cycles:
1. Dry steam plants are the simplest and oldest design. They directly use geothermal steam of 150°C or more to turn turbines.
2. Flash steam plants pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines. They require fluid temperatures of at least 180°C, usually more. This is the most common type of plant in operation today.
3. Binary cycle power plants are the most recent development, and can accept fluid temperatures as low as 57°C. The moderately hot geothermal water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash to vapor, which then drives the turbines. This is the most common type of geothermal electricity plant being built today. Both Organic Rankine and Kalina cycles are used. The thermal efficiency is typically about 10%.