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Heating with geothermal systems 179

by dividing the actual heat utilization by the maximum possible utilization if the
installed capacity operated for a full year.
In many cases, geothermal plays a significant part in a country’s thermal energy
supply system or energy infrastructure. A few of these are described below.
• Iceland: Geothermal hot water from numerous fields is piped to cities and towns to cover
90% of the space heating needs of buildings in the entire country.
• Japan: There is a thriving balneology industry in Japan owing to the national culture of
visiting hot spring spas (onsen, in Japanese). The statistics are impressive: 2000 onsens,
5000 public baths, and 1500 hotels serving 15 million guests per year.
• Sweden: As a cold-weather country, Sweden heats 20% of all buildings using geothermal
heat pumps.
• Switzerland: A European leader in geothermal heat pumps, Switzerland has 90,000 units
installed or about 2.25 units per square kilometer of total area, a remarkable figure given
that only 6.8% of the country’s land area is covered with buildings and residences. Thus there
is a rate of 33 units per inhabited square kilometer.
• Turkey: Favored with many geothermal resources, most of low-to-moderate temperature,
Turkey has 90,000 apartment residences geothermally heated in 16 cities, nearly 30% of
the total units in the country. Turkey is also the world leader in geothermal greenhouses
with 300 ha in operation.
• United States: There are 1.4 million geothermal heat pumps providing full comfort control in
residences and buildings, and the growth rate is strong at 7.0% per year.
Table 5.2 lists the top ten countries by installed capacity, heat utilization, and capac-
ity factor. Not surprisingly the same ten countries appear in the first two categories.
Ten relatively small countries rank as the best in capacity factor. Also notice that
the top ten countries account for roughly 80% of all the world’s capacity and utilization
of geothermal heat that is distributed among 82 countries.

5.2 Modern technology, geothermal field development,
and geothermal heating systems

Geothermal energy has been recognized for millennia by the inhabitants of planet
Earth, who both feared its power and devised means to capture it for useful purposes
[3]. In this section we discuss ways to find exploitable geothermal resources using
modern technology, drilling techniques that reach several kilometers into the earth
to unlock the potential, and systems for distributing that energy to consumers.

5.2.1 Exploration
In early times one need not have advanced degrees or highly trained personnel to
recognize geothermal resources. Nature revealed these subterranean caches of energy
through surface thermal manifestations such as hot springs, steam vents or fumaroles,
mineral deposits such as sulfur, obsidian or calcite, spectacular geysers, and patches of
altered hot ground. Early peoples were attracted to places with such characteristics and