Overview of Geothermal energy
Low Temperature Geothermal
When the term "geothermal" is used in the context of energy the
term tends to engender images of shooting geysers and bubbling lava.
Certainly this type of energy generation known as "High Temperature
Geothermal" exists in many parts of the U.S. and is discussed in
detail in our section on Geothermal Plants. However, for most
homeowners the most exciting story when it comes to renewable energy
is low temperature geothermal using a type of heating system called a
ground source heat pump. This type of heating leverages the fact that
the temperature of the earth in your front and back yard remains very
stable throughout the year at between 45°
- 75° degrees Fahrenheit. By
leveraging these constant temperatures it is possible to heat and cool
your home geothermally at substantially less cost than you probably do
today. In an era where natural gas and heating oil prices have
gone through the roof, a ground source heat pump is something that
just about every homeowner ought to consider.
Geothermal energy is a bi-directional energy source that can be
used for both heating and cooling. When using geothermal energy
for cooling in the summer heat pumps are used to extract the
hotter air from the house so that it can be cooled in the earth. In
the winter the outside air is colder than the ground temperature and
so the heat exchanger in the heat pump can move the heat from the
ground into the house or building.
Ground source heat pump systems can save you substantial money on
your home heating and cooling bill. Most studies indicate that
geothermal heating and cooling can lead to savings between 25%-50%
over conventional heating and cooling systems. While they do have an
upfront cost, the payback period is relatively short, between 2-10
years depending upon the installation. Given recent changes in heating
oil and natural gas prices the savings are likely to be even greater
in the future and payback periods even shorter. For more
information on costs check out the Typical Costs section. Also, there
are federal tax credits available for geothermal heating and many
states provide incentives as well. You can find information on
incentives in our Incentives section.
In addition to lower cost, ground source heat pumps offer a number
of other advantages over a conventional furnace. Ground source
heat pumps run on electricity. This means they are exceptionally
safe. There is no combustion and no combustion gases such as
methane are released. This means it is not only safer for you,
it is better for the environment as well. Heat pumps also tend
to provide a more even heat than traditional furnaces and usually run
High Temperature Geothermal
The direct use of geothermal heating has been practiced for thousands of years, and direct use continues today.
Many parts of the world, particularly those in the regions which
border the earth's tectonic plates (sometimes called the ring of fire)
have strong access to geothermal sources close to the surface.
In the United States there are extensive geothermal sources in the
west and northwest. These geothermal sources can be tapped
directly or indirectly and then used for heating buildings, streets or
districts. The heat is also used in heating spas and pools, in aquaculture and greenhouses, and in various industrial applications.
For information on direct uses of geothermal heating look at our
section on Geothermal Heating in the Geothermal Plants section.
Another use of geothermal energy is electric power generation. Electric power generation using geothermal resources may take place in several different types of plants, but most rely on the process of piping water or steam into a plant from
an underground heat source. The steam is used to run a
conventional steam turbine when then generates the electricity.
Because there is no need to use natural gas or oil to heat the water
and create steam, these types of plants can be extremely efficient and
can generate enough electricity to feed thousands and sometimes tens
of thousands of homes. Moreover they do this without adding any
hydrocarbons or pollutants to the atmosphere. For information on
electric generation with geothermal look at our section on Geothermal
Electric in the Geothermal Plants section.
Direct access to geothermal sources and electrical generation
through tapping geothermal sources are often referred to as High
Temperature Geothermal in that they are leveraging extremely high
temperature underground sources. These sources are usually only
found in specific geological areas adjacent to the earth's tectonic
plates. However, it is also possible to develop useful energy by
leveraging the differential that exists between air temperature and
ground temperature near the surface. These types of Low
Temperature Geothermal systems are called Geo-exchange systems, and
constitute a third category of geothermal energy use.
High temperature geothermal energy systems require significant
physical infrastructure and therefore are generally restricted to
large heating or electric plants. However, low temperature
geothermal exchange systems using heat pumps are much simpler and can
be used by most home or small business owners. They are becoming
increasingly common throughout the United States and Europe and are
one of the most promising renewable energy approaches.