Page 408 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

372 part III The Earth–Atmosphere Interface
F cus Study 12.2 Sustainable resources Heat from Earth—Geothermal Energy and Power
Geothermal energy, the tremendous amount of endogenic heat within Earth’s interior, can in some places be harnessed for heating and power production by means of wells and pipes that transmit heated water or steam to the surface. Underground reservoirs of hot water at varying depths and temperatures are among the geothermal resources that can be tapped and brought to the surface. resources of this kind provide direct geo- thermal heating, which uses water at low- to-moderate temperatures (20°C to 150°C) in heat-exchange systems in buildings, commercial greenhouses, and fish farms, among many examples. Where available, direct geothermal heating provides en- ergy that is inexpensive and clean.
In Boise, Idaho, which has used geo- thermal resources for decades, the state capitol building uses direct geothermal heating, and most city locations return used geothermal water to the aquifer through injection wells. In reykjavík, Ice- land, the majority of space heating sys- tems (more than 87%) are geothermal.
Geothermal Power Production
Geothermal electricity is produced
using steam from a natural underground reservoir to drive a turbine that powers
a generator. Because the steam comes directly from Earth’s interior (without burning fuel to produce it), geothermal electricity is a relatively clean energy. Ideally, groundwater for this purpose should have a temperature of from
180°C to 350°C and be moving through rock of high porosity and permeability (allowing the water to move freely through connecting pore spaces). The geysers geothermal Field in northern California (so named despite the absence of any geysers in the area) is the largest geothermal power production plant using this method in the world (Figure 12.2.1).
Today, geothermal applications are
in use in 70 countries and include over 200 power plants producing a total output of about 11000 MW. The top countries for installed geothermal elec- trical generation are the United States, Philippines, Indonesia, Mexico, Italy,
new Zealand, Iceland, and Japan. In the Philippines, almost 27% of total electrical production is generated with geothermal energy; in Iceland, the percentage is 30% (Figure 12.2.2).
▲Figure 12.2.1 Geysers Geothermal Field, California. [James P. Blair/national geographic.]
In Canada, there are no geothermal energy power plants operating at pres- ent. Studies for geothermal energy production have been conducted at Mount Meager near Pemberton, British Columbia, and underground reservoirs are used to store heat for buildings at Carleton University in Ottawa and the municipal centre in Scarborough, On- tario. About 30 000 homes use ground- source heat pumps that take advantage of temperature differences between ground and air, both in winter and summer.
For more information, see www .cangea.ca, energy.gov/eere/geothermal/ geothermal-technologies-office, or www .geothermal.org. A map of potential geo- thermal energy resources in Canada is in Figure 12.2.3.
The newest geothermal technology seeks to create conditions for geothermal power production at locations where underground rock temperatures are
high but where water or permeability
is lacking. In an enhanced geothermal system (EgS), cold water is pumped underground into hot rock, causing the rock to fracture and become permeable to water flow; the cold water, in turn, is heated to steam as it flows through the high-temperature rock.
Several EgS projects are either operational or under development worldwide; the largest of these is in
Australia’s Cooper Basin. The potential for EgS, as with other geothermal technologies, is highest in areas of
the world along plate boundaries that produce upwelling pockets of magma and volcanic activity.
Geothermal as a Sustainable Resource
geothermal power production has many advantages, including minimal production of carbon dioxide (CO2 is released during the extraction of steam, but in far smaller amounts than the CO2 emitted to the atmosphere from the use of fossil fuels). geothermal power can be produced 24 hours a day, an advantage when compared with solar or wind energy, in which the tim- ing of production is linked to daylight or other natural variations in the resource.
Although geothermal is billed as renewable and self-sustaining, research shows that some geysers and geothermal fields are being depleted as the extraction rate exceeds the rate of recharge. In addition, the drilling of wells or the injection or removal of water in connection with geothermal energy projects may pose some risk of induced seismicity
(that is, minor earthquakes and tremors produced in association with human activity, discussed further in Chapter 13). In Switzerland, geothermal power developers are working on technology
FPO