Page 24 - Geothermal Energy Renewable Energy and The Environment

6 Geothermal Energy: Renewable Energy and the Environment

the temperature at depths of 3–10 meters is usually constant because of the flow of heat from the
interior of the Earth. That heat can be used as a source of energy for heating, ventilating and air con-
ditioning (HVAC) buildings using ground source heat pumps (GSHP; Chapter 10). Due to their high
efficiency, GSHP use diminishes electrical demand. When combined with programs that improve
building efficiency, such applications of geothermal energy can displace a significant percentage of
electricity generation that is required to meet the HVAC load.
In many areas, modest heat flow is available to allow the use of geothermal energy for industrial
applications that currently rely on fossil fuels. These direct use applications include food process-
ing, drying materials, agricultural activities and greenhouses, aquaculture, paper manufacturing,
and so on. Although such applications have been developed and successfully used throughout the
world, they remain relatively unknown and vastly underutilized. Chapter 11 discusses many of these
applications.
In regions where geothermal energy occurs at a higher density, as discussed in Chapters 2 and
9, temperatures are high enough to allow the generation of electrical power. Figure 1.5 shows a
comparison of CO emissions for fossil-fueled power generation compared to geothermal plants.
2
Geothermal power generation in appropriate settings can effect a very significant reduction in
greenhouse gas emissions. As discussed in Chapter 2, current geothermal power generation technol-
ogy has application in specific geological settings and thus is not currently able to provide electrical
power in all settings. For this reason, its application is restricted to about 30% of the geographical
area of the United States. However, as discussed in Chapter 14, the development of new technology
that allows the drilling and use of deeper wells and geothermal reservoirs will expand deployment
of geothermal generation capabilities to most regions of every continental land mass. It is currently
anticipated that this new technology could supply a large fraction of U.S. electrical power by 2050
(Tester et al. 2006).
Deployment of geothermal energy technologies will be most effective where the attributes of
the technology are matched to the characteristics and needs of the energy sector they are designed

1200

Coal

900 Oil
CO 2 emissions (kgs/MWh) 600 Natural

gas

300
Geothermal -
flash

0
FIGUre 1.5 CO 2 emissions (in kg of CO 2 /MWh) for different power generating technologies. The values
for the generating systems that use fossil fuels are from the U.S. Environmental Protection Agency eGrid
2000 database. The data for geothermal power technologies is from Slack (2009). Binary geothermal power
generation produces no emissions. (From K. Slack, Geothermal resources and climate emissions, Geothermal
Energy Association, Washington, DC, Draft Report for Public Review, 2009.)