Technology Status - NET Nowak Energie & Technologie AG

Wastewater: Discharge of wastewater is also a potential source of chemical
pollution. Spent geothermal fluids with high concentrations of chemicals
such as boron, fluoride or arsenic should be treated, and/or re-injected into
the reservoir. However, the low-to-moderate temperature geothermal fluids
used in most direct-use applications generally contain low levels of
chemicals and the discharge of spent geothermal fluids is seldom a major
problem. Sometimes these fluids can be discharged into surface water after
cooling. The water can then be cooled in special storage ponds or tanks to
avoid modifying the ecosystems of natural bodies of water.
Ground subsidence: Extraction of large quantities of fluids from geothermal
reservoirs may result in ground subsidence. Subsidence should be
monitored systematically, as it could damage the geothermal plant and other
buildings in the area. In many cases, subsidence can be prevented or reduced
by re-injecting the geothermal wastewater.
Seismic activity: The withdrawal and/or re-injection of geothermal fluids
may trigger or increase the frequency of seismic events in certain areas.
However these are micro-seismic events that can only be detected by
instrumentation. Exploitation of geothermal resources is unlikely to trigger
major seismic events.
Sustainability: Geothermal energy is usually classified as renewable and
sustainable. “Renewable” describes a property of the energy source, whereas
“sustainable” describes how the resource is used. On a site-by-site basis,
geothermal energy is renewable if the use of energy is adapted to the natural
rate of energy recharge. Usually geothermal power plants can operate for
about 50 years at a site (sometimes longer), implying a decline of the heat
content of the geothermal reservoir, which subsequently needs a recovery
period of several decades.
Noise: Geothermal plants produce noise pollution during construction, e.g.
by drilling of wells and the escape of high-pressure steam during testing.
Noise is usually negligible during operation with direct-heat applications.
However, electricity generation plants produce some noise from the cooling
tower fans, the steam ejector and the turbine.
Visual impact: Geothermal plants are often located in areas of high scenic
value, where the appearance of the plant is important. Fortunately,
geothermal power plants take up little area and, with careful design they can
blend well into the surrounding environment. Wet cooling towers at plants
can produce plumes of water vapour, which some people find unsightly. In
such cases, air-cooled condensers can be used.
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