TERRESTRIAL HEAT – energy from the inside of energy from the inside of

the Earththe Earth

What does “geothermal“ mean?

The term geothermal comes from the Greek geo meaning earth and therine meaning heat thus geothermal energy is energy derived from the natural heat of the earth.

The heat inside the Earth core is continually generated by the decay of the long lived radioactive isotopes of uranium,  thorium and potassium, which are present in the Earth.

The heat that flows from the Earth's hot interior due to plate movements, zones of high heat flow, may be located close to the surface where convective circulation plays a significant role in bringing the heat close to the surface

What happens with the heat?

Without utilization, the terrestrial heat flow is lost to the atmosphere. In this case, the isotherms run parallel to the earth’s surface and the heat flow lines are perpendicular to them. If, instead, the heat flow can be captured, the isotherms are deformed and the heat flow lines can be diverted towards heat sinks.

Due to variations of the earth’s crust thickness there will be different temperature profiles from place to place. Some areas are known to have hot springs and the like and volcanic activities, such areas will also be well suited for geothermal utilization.

How does geothermal heat get up to the surface? Sometimes the hot magma

reaches all the way to the surface, where we know it as lava. But most often the magma remains below earth's crust, heating nearby rock and water (rainwater that has seeped deep into the earth) - sometimes as hot as 700 degrees F. Some of this hot geothermal water travels back up through faults and cracks and reaches the earth's surface as hot springs or geysers, but most of it stays deep underground, trapped in cracks and porous rock. This natural collection of hot water is called a geothermal reservoir.

Best locations Geothermal systems can be found in

regions with a normal or slightly above normal geothermal gradient.

The margins of the plates correspond to weak, densely fractured zones of the crust, characterized by an intense seismic activity, by a large number of volcanoes and, because of the ascent of very hot materials towards the surface, by a high terrestrial heat flow. The most important geothermal areas are located around plate margins.

World pattern of plates, oceanic ridges, oceanic trenches, subduction zones, and geothermal fields.

Accessing geothermal energy

If geothermal reservoirs are close enough to the surface, we can reach them by drilling wells, sometimes over two miles deep. Scientists and engineers use geological, electrical, magnetic, geochemical and seismic surveys to help locate the reservoirs. Then, after an exploration well confirms a reservoir discovery, production wells are drilled.

Geothermal system 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". 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.

Generating electricity : Geothermal power plants

In geothermal power plants, we use the natural hot water and steam from the earth to turn turbine generators to produce electricity. Unlike fossil fuel power plants, no fuel is burned. Geothermal power plants give off water vapour, but have no smoky emissions.

There are several different types of plants: flashed steam plants, dry steam plants and binary power plants

Flashed Steam Plants

Most geothermal power plants operating today are "flashed steam" power plants. Hot water from production wells is passed through one or two separators where, released from the pressure of the deep reservoir, part of it flashes (explosively boils) to steam. The force of the steam is used to spin the turbine generator. To conserve the water and maintain reservoir pressure, the geothermal water and condensed steam are directed down an injection well back into the periphery of the reservoir, to be reheated and recycled.

Flash steam power plants use hot water reservoirs. In flash plants, as hot water is released from the pressure of the deep reservoir in a flash tank, some if it flashes to steam.

Dry Steam Plants A few geothermal reservoirs

produce mostly steam and very little water. Here, the steam shoots directly through a rock-catcher and into the turbine. The first geothermal power plant was a dry steam plant, built at Larderello in Tuscany, Italy in 1904. The power plants at the Larderello dry steam field were destroyed during World War II, but have since been rebuilt and expanded. That field is still producing electricity today. The Geysers dry steam reservoir in northern California has been producing electricity since 1960. It is the largest known dry steam field in the world and, after 40 years, still produces enough electricity to supply a city the size of San Francisco.

Binary Power Plants

In a binary power plant, the geothermal water is passed through one side of a heat exchanger, where it's heat is transferred to a second (binary) liquid, called a working fluid, in an adjacent separate pipe loop. The working fluid boils to vapour which, like steam, powers the turbine generator. It is then condensed back to a liquid and used over and over again. The geothermal water passes only through the heat exchanger and is immediately recycled back into the reservoir. In some power plants, flash and binary processes are combined.

Direct (non-electrical) uses of geothermal water

Shallower reservoirs of lower temperature -- 21-149°C (70-300°F) are used directly in health spas, greenhouses, fish farms, and industry and in space heating systems for homes, schools and offices.

It is only during the last century that we have used geothermal energy to produce electricity. But using geothermal water to make our lives more comfortable is not new: people have used it since the dawn of mankind. Wherever geothermal water is available, people find creative ways to use its heat.

Agriculture and aquaculture

Geothermal energy is used directly in agriculture and aquaculture:

to help grow flowers, vegetables, and other crops in greenhouses while snow-drifts pile up outside

to shorten the time needed for growing fish, shrimp, abalone and alligators to maturity

Industry

The heat from geothermal water is used worldwide for industrial purposes. Some of these uses include drying fish, fruits, vegetables and timber products, washing wool, dying cloth, manufacturing paper and pasteurizing milk.

Geothermally heated water can be piped under sidewalks and roads to keep them from icing over in freezing weather. Thermal waters are also used to help extract gold and silver from ore and even for

refrigeration and ice-making.

Hot Spring Bathing and Spas (Balneology)

For centuries, peoples of China, Iceland, Japan, New Zealand, North America and other areas have used hot springs for cooking and bathing. The Romans used geothermal water to treat eye and skin disease and, at Pompeii, to heat buildings. Medieval wars were even fought over lands with hot springs.

In Europe, natural hot springs have been very popular health attractions. The first known "health spa" was established in 1326 in Belgium. (One resort was named "Espa" which means "fountain." The English word "spa" came from this name.) All over Eurasia today, health spas are still very popular. Russia, for example, has 3,500 spas.

Japan is considered the world’s leader in balneology. The Japanese tradition of social bathing dates back to ancient Buddhist rituals. Beppu, Japan, has 4,000 hot springs and bathing facilities that attract 12 million tourists a year. Other countries with major spas and hot springs include New Zealand, Mexico and the United States.

District heating The oldest and most common use of

geothermal water, apart from hot spring bathing, is to heat individual buildings, and sometimes entire commercial and residential districts.

A geothermal district heating system supplies heat by pumping geothermal water -usually 60° C (140°F) or hotter- from one or more wells drilled into a geothermal reservoir. The geothermal water is passed through a heat exchanger which transfers the heat to water in separate pipes that is pumped to the buildings. After passing through the heat exchanger, the geothermal water is injected back into the reservoir where it can reheat and be used again.

Because it is a clean, economical method of heating buildings, geothermal district heating is becoming more popular in many places. The world's largest geothermal district heating system is in Reykjavik, Iceland, where almost all the buildings use geothermal heat. The air around Reykjavik was once very polluted by emissions from reliance on fossil fuels. Since it started using geothermal energy, Reykjavik has become one of the cleanest cities in the world.

Geothermal heat pumps The heat pumps are machines that move

heat in a direction opposite to that in which it would tend to go naturally, i.e. from a cold space or body to a warmer one. A heat pump is effectively nothing more than a refrigeration unit. Any refrigeration device (window air conditioner, refrigerator, freezer, etc.) moves heat from a space (to keep it cool) and discharges that heat at higher temperatures. The only difference between a heat pump and a refrigeration unit is the desired effect, cooling for the refrigeration unit and heating for the heat pump. A second distinguishing factor of many heat pumps is that they are reversible and can provide either heating or cooling in the space.

Geothermal heat pumps reduce electricity use 30-60% compared with traditional heating and cooling systems, because the electricity which powers them is used only to move heat, not to produce it. The U.S. Environmental Protection Agency rates geothermal heat pumps among the most efficient of heating and cooling technologies.

Advantages of geothermal energy

RENEWABILITY AND SUSTAINABILITY :Earth’s heat is continuously radiated from within, and each year rainfall and snowmelt supply new water to geothermal reservoirs. Production from individual geothermal fields can be sustained for decades and perhaps centuries. The U.S. Department of Energy classifies geothermal energy as renewable.

CONSERVATION OF RESOURCES : When we use renewable geothermal energy for direct use or for producing electricity, we conserve exhaustible and more polluting resources like fossil fuels and uranium. Installed geothermal electricity generation capacity around the world is equivalent to the output of about 10 nuclear plants.

PROTECTION OF THE ENVIRONMENT: Geothermal direct use facilities have minimal or no negative impacts on the environment. Geothermal power plants are relatively easy on the environment.

Protection of the Air and Atmosphere. Hydrogen sulphide gas (H2S) sometimes occurs in geothermal reservoirs. It is subject to regulatory controls for worker safety because it can be toxic at high concentrations. Equipment for scrubbing H2S from geothermal steam removes 99% of this gas. Carbon dioxide CO2 occurs naturally in geothermal steam but the geothermal plants release amounts less than 4% of that released by fossil fuel plants. And there are no emissions at all when closed-cycle (binary) technology is used.

Visual Protection. A geothermal plant sits right on top of its fuel source: no additional land is needed such as for mining coal or for transporting oil or gas. When geothermal power plants and drill rigs are located in scenic areas, mitigation measures are implemented to reduce intrusion on the visual landscape.

LOW COSTS: the price of geothermal power decreased with about 25 % in the last 2 decades due to the development of the technology used and the involvement of the government in the research regarding this domain.

Future of geothermal energyThe outlook for geothermal energy use depends on at least three factors: The Demand for energy will continue to grow. Economies are expanding, populations are

increasing (over 2 billion people still do not have electricity), and energy-intensive technologies are spreading. All mean greater demand for energy.

The Inventory of accessible geothermal energy is sizable. Using current technology geothermal energy from already-identified reservoirs can contribute as much as 10% of the United States energy supply. And with more exploration, the inventory can become larger. The entire world resource base of geothermal energy has been calculated in government surveys to be larger than the resource bases of coal, oil, gas and uranium combined

The Competitive Position depends primarily on cost: Costs: Shorter and Longer Term. Production of fossil fuels (oil, natural gas and coal) are

a relative bargain in the short term. Like many renewable resources, geothermal resources need relatively high initial investments to access the heat, hot water and steam. But the geothermal "fuel" cost is predictable and stable. Renewable geothermal energy is a better long term investment.

Costs: Direct and Indirect. The monetary price we pay to our natural gas and electricity suppliers, and at the gas pump, is our direct cost for the energy we use. Geothermal energy is a clean, indigenous, renewable resource without hidden external costs.

Costs: Domestic and Importing. Investment in the use of domestic, indigenous, renewable energy resources like geothermal energy provides jobs, expands the regional and national economies, and avoids the export of money to import fuels.

Conclusion:

Energy demand is increasing rapidly worldwide. Some energy and environmental experts predict that the growth of electricity production and direct uses of geothermal energy will be revitalized by international commitments to reduce carbon dioxide emissions to avert global climate change and by the opening of markets to competition.

Made by : Diana GiurghitaDiana Giurghita

&&Anca MunteanAnca Muntean