10-08-2012, 12:08 PM
Basics of Geothermal Energy Production and Use
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INTRODUCTION
Geothermal energy, the heat of the Earth, provides continuous, 24-hour a day, clean, sustainable
energy production. Together, advances in technology, private investment, and government
support are increasing geothermal energy production in the U.S. and worldwide. Geothermal
101: Basics of Geothermal Energy Production and Use gives an overview of what you should
know about this renewable energy resource. It includes simple definitions, descriptions, and
figures and cites key national reports that provide further information. The benefits of using
geothermal energy are explained on a national, economic and environmental level. This report
answers the common questions about geothermal energy and provides you with up-to-date
information and references. Although more emphasis is given in this report to geothermal
electricity production, other applications such as geothermal heat pumps and direct heating uses
are also covered. Whether you are new to the basics or have been working in the field for years,
this report provides valuable information.
BASICS
What is geothermal energy?
Geothermal energy is defined as heat from the Earth. It is a clean, renewable resource that
provides energy in the U.S. and around the world in a variety of applications and resources.
Although areas with telltale signs like hot springs are more obvious and are often the first places
geothermal resources are used, the heat of the earth is available everywhere, and we are learning
to use it in a broader diversity of circumstances. It is considered a renewable resource because
the heat emanating from the interior of the Earth is essentially limitless. The heat continuously
flowing from the Earths interior, which travels primarily by conduction, is estimated to be
equivalent to 42 million megawatts (MW) of power, and is expected to remain so for billions of
years to come, ensuring an inexhaustible supply of energy.(1)
How does a conventional geothermal reservoir work?
A geothermal system requires heat, permeability, and water. The heat from the Earth’s core
continuously flows outward. Sometimes the heat, as magma, reaches the surface as lava, but it
usually remains below the Earth’s crust, heating nearby rock and water sometimes to levels as
hot as 700°F. When water is heated by the earths heat, hot water or steam can be trapped in
permeable and porous rocks under a layer of impermeable rock and a geothermal reservoir can
form. This hot geothermal water can manifest itself on the 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.
Geothermal Heat Pumps (GHPs):
Geothermal heat pumps take advantage of the Earths relatively constant temperature at depths of about 10 ft to 300 ft. GHPs can be
used almost everywhere in the world, as they do not share the requirements of
fractured rock and water as are needed for a conventional geothermal reservoir. GHPs
circulate water or other liquids through pipes buried in a continuous loop, either
horizontally or vertically, under a landscaped area, parking lot, or any number of areas
around the building. The Environmental Protection Agency considers them to be one
of the most efficient heating and cooling systems available.
Animals burrow underground for warmth in the winter and to escape the heat of the
summer. The same idea is applied to GHPs, which provide both heating and cooling
solutions. To supply heat, the system pulls heat from the Earth through the loop and
distributes it through a conventional duct system. For cooling, the process is reversed;
the system extracts heat from the building and moves it back into the earth loop. It can
also direct the heat to a hot water tank, providing another advantage free hot water.
GHPs reduce electricity use 3060% compared with traditional heating and cooling
systems, because the electricity which powers them is used only to collect,
concentrate, and deliver heat, not to produce it.