Geothermal - Energy Policy Analysis: A Conceptual Framework - page 137

Water Usage
Most geothermal power plants require a large amount of water for cooling towers or other purposes
(DiPippo 2008, 104). In places where water is in short supply, this need could raise conflicts with
other users for water resources (Brower 1992). Geothermal fluids contain elevated levels of ar-
senic, mercury, lithium, and boron because of underground contact between hot fluids and rocks.
If waste is released into rivers or lakes instead of being injected into the geothermal field, these
pollutants can damage aquatic life and make the water unsafe for drinking or irrigation (Stewart
2009). Geothermal plants of all types discharge more waste heat per unit of power output than
other thermal power plants (DiPippo 2008, 183), so it is imperative that some beneficial use, such
as greenhouse heating, should be found for the waste heat; alternatively, cooling towers could be
used or the waste fluids could be reinjected into the geothermal reservoir.
Noise Pollution
Drilling and well testing, which requires periodic venting of geothermal steam and gases directly
to the atmosphere, generate loud hissing and whistling noises on-site, which may be irritating to
nearby residents, livestock, and wildlife. This noise pollution must be controlled using mechanical
means (DiPippo 2008, 104).
Future Developments
A new approach to capturing the heat in dry areas is known as enhanced geothermal systems
(EGS) or “hot dry rock.” Hot dry rock reservoirs, typically at greater depths below the earth's
surface than conventional sources, are first broken up by pumping high-pressure water through
them. More water is then pumped through the broken hot rocks, where it heats up, returns to the
surface as steam, and powers turbines to generate electricity. Water is returned to the reservoir
through injection wells to complete the circulation loop (UCS 2009).
The U.S. Department of Energy, several universities, the geothermal industry, and venture capital
firms (including Google) are collaborating on research and demonstration projects to harness the
potential of hot dry rock. DOE, which has funded several demonstration projects, hopes to have
EGS ready for commercial development by 2015 (UCS 2009). One cause for careful consideration
with EGS is the possibility of induced seismic activity that might occur from hot dry rock drilling
and development. This risk is similar to that associated with hydraulic fracturing (fracking), an
increasingly used, controversial method of oil and gas drilling, and with carbon dioxide capture
and storage in deep saline aquifers (UCS 2009). There is sound evidence that the frequency of
local earthquakes can be increased by injection of fluids in deep wells (Scanlon 1992, 6; Hsieh
and Bredehoeft 1981).
Oil and gas fields already in production represent another large potential source of geothermal
energy. In many existing oil and gas reservoirs, a significant amount of high-temperature water
or suitable high-pressure conditions are present, which could allow for production of electricity
with oil or gas at the same time. In some cases, exploiting these resources may enhance extraction
of oil and gas (UCS 2009). An MIT study estimated that the United States has the potential to
develop 44,000 MWe of geothermal capacity by 2050 by coproducing geothermal electricity, oil,
and natural gas at oil and gas fields—primarily in the Southeast and southern Plains states. The
study projects that such advanced geothermal systems could supply 10 percent of U.S. baseload
electricity by that year, given research and development and related deployment in the interim
(Tester et al. 2006).