1.  What is Geothermal Energy?


Geothermal Reservoir

Geothermal energy is the heat from the Earth. the heat contained within the Earth that generates geological phenomena on a planetary scale. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.


Renewable Energy

Geothermal energy is clean and sustainable. It’s often used nowadays, however, to indicate that part of the Earth’s heat that can, or could, be recovered and exploited by man, and it is in this sense that we will use the term from now on.

 2.      What is a geothermal system and what happens in such a system?


Schematic representation of an ideal geothermal system

It can be described schematically as ‘convecting water in the upper crust of the Earth, which, in a confined space, transfers heat from a heat source to a heat sink, usually the free surface’ (Hochstein, 1990). A geothermal system is made up of three main elements: a heat source, a reservoir and a fluid, which is the carrier that transfers the heat. The heat source can be either a very high temperature (> 600 °C) magmatic intrusion that has reached relatively shallow depths (5-10 km) or, as in certain low-temperature systems, the Earth’s normal temperature, and increases with depth. The reservoir is a volume of hot permeable rocks from which the circulating fluids extract heat. The reservoir is generally overlain by a cover of impermeable rocks and connected to a surficial recharge area through which the meteoric waters can replace or partly replace the fluids that escape from the reservoir through springs or are extracted by boreholes. The geothermal fluid is water, in the majority of cases meteoric water, in the liquid or vapour phase, depending on its temperature and pressure. This water often carries with it chemicals and gases such as CO2, H2S, etc.

 3.        Geothermal Direct Use

When a person takes a hot bath, the heat from the water will usually warm up the entire bathroom. Geothermal reservoirs of hot water, which are found a couple of miles or more beneath the Earth’s surface, can also be used to provide heat directly. This is called the direct use of geothermal energy.


How to use geothermal energy

In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water. The water is brought up through the well, and a mechanical system – piping, a heat exchanger, and controls – delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes of it on the surface.

 4.        Geothermal Energy Recources

Below the Earth’s crust, there is a layer of hot and molten rock called magma. Heat is continually produced there, mostly from the decay of naturally radioactive materials such as uranium and potassium. The amount of heat within 10,000 meters (about 33,000 feet) of Earth’s surface contains 50,000 times more energy than all the oil and natural gas resources in the world.


Geothermal Potensial

The areas with the highest underground temperatures are in regions with active or geologically young volcanoes. These “hot spots” occur at plate boundaries or at places where the crust is thin enough to let the heat through. The Pacific Rim, often called the Ring of Fire for its many volcanoes, has many hot spots, including some in Alaska, California, and Oregon. Nevada has hundreds of hot spots, covering much of the northern part of the state.

These regions are also seismically active. Earthquakes and magma movement break up the rock covering, allowing water to circulate. As the water rises to the surface, natural hot springs and geysers occur, such as Old Faithful at Yellowstone National Park. The water in these systems can be more than 200°C (430°F).

 5.        The Future of Geothermal Energy


Geothermal Energy

Geothermal energy has the potential to play a significant role in moving the United States (and other regions of the world) toward a cleaner, more sustainable energy system. It is one of the few renewable energy technologies that—like fossil fuels—can supply continuous, baseload power. The costs for electricity from geothermal facilities are also declining. Some geothermal facilities have realized at least 50 percent reductions in the price of electricity since 1980. A considerable portion of potential geothermal resources will be able produce electricity for as little as 8 cents per kilowatt-hour (including a production tax credit), a cost level competitive with new conventional fossil fuel-fired power plants. There is also a bright future for the direct use of geothermal resources as a heating source for homes and businesses in any location.

 6.         Geothermal Energy in Indonesia                                               


Indonesia Geothermal Working Area Map

Indonesia presents one of the world’s most attractive geothermal regions. Indonesia has about 40% of world wide known resources, which are widely distributed, generally highly productive and high enthalpy resources and estimated will generate 27,000 MW of electricity.

Indonesia possesses a variety of energy resources. Energy diversification needs, rising concern over environmental issues, and declining non-renewable energy resources have also prompted greater interest in geothermal and hydropower. Indonesia National energy mix in 2025 has also set target to enhance geothermal energy proportion from 1% to 4%.

The Government’s recent moves to increase petroleum fuel prices, which have long diminished the viability of more environmentally friendly energy sources, may stimulate further utilization of alternative, including renewable, and energy resources.


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