Geothermal power

From ArticleWorld

Geothermal power is the electricity which is generated after harnessing intense heat present in rocks inside the earth’s crust. The heat continuously flows outwards, away from the centre of the earth. The heat may be generated due to radioactivity in rocks deep within; but geothermal energy originates mainly from the hot molten core of the earth, which consists of metals at temperatures in several thousand degrees Celsius. A form of renewable energy, this contributes to less than 2% of the world’s energy requirements. About 8000 megawatts of installed capacity in more than 20 countries is based on geothermal energy.

Sources of geothermal energy – their types

Heat present inside rocks deep within the earth’s crust can be tapped in a number of ways:

1. Electricity can be generated on a large scale by utilising natural steam emerging from geysers.
2. Another method could be the use of hot springs or superheated ground water in order to be used for running turbines, after being sufficiently superheated.
3. Geothermal heat can also be utilised to heat a ‘heat exchanger’ fluid circulated through rocks.

Another method of capturing geothermal energy is the ‘hot dry-rock’ method. Still in an experimental stage and not yet proved to be economically viable, this method involves the pumping of water into hot rock spaces to prepare steam. Technology that exists does not provide for capturing of the magma’s heat, when it appears sufficiently close to the surface of the earth. The magma is present in a subterranean region of hot molten rock, and can result in temperatures of up to 350°C inside geothermal reservoirs.

Electrical generation

The number of sites where geothermal energy can be extracted economically is limited. The United States, the Philippines, Italy, Mexico, Indonesia, Japan, New Zealand and Iceland are the largest producers of geothermal power. There are a number of hot springs in India as well. Geothermal reservoirs are reached by drilling through the crust up to 5km. The hot water or steam is used to turn turbines to generate electricity. There are three types of geothermal plants: flash steam plants, dry steam plants, and binary plants.

Flash steam plants utilise the sudden release of high pressure from underground reservoirs to run turbines. Some of the hot water flashes to steam due to the sudden reduction in pressure. While most geothermal plants produce hot water, some may produce steam also. In such cases, the steam is directly sent to a dry steam plant to run a turbine-generator set.

Binary power plants utilise heat exchangers, as mentioned in the section on ‘sources of geothermal energy – their types’. The heat exchanger used may be isobutane, since it has a low-boiling point and can be repeatedly vaporised in order to run a turbine system.

Drawbacks of geothermal power

1. Power generation using geothermal energy is very uncommon because of the rarity of geothermal steam fields.
2. At many times, though geothermal energy is supposed to be renewable, water injection may be required due to reduced content of water in the reservoirs.
3. Geothermal sites may eventually cool down, hence the opinion that, strictly speaking, this form of energy is not renewable.

In spite of being environment friendly, low in cost and highly efficient, in most cases, geothermal energy has not proven very exploitable – this technology is still at a young stage and is a subject of research the world over.