Geothermal handbook: PlanninG and Financing power Generation t e c h n I c a L r e p o r t 2 / 2

F I g u r E 1 . 2
World Map of Tectonic Plate Boundaries
Source | US Geological Survey.

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C h a p t e r 1
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USGS on www.cnsm.csulb.edu
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Industry professionals often use the terms “high-enthalpy” and “high-temperature” as synonyms when describing geothermal resources 
(Elíasson 2001). Enthalpy is a measure of the total energy of a thermodynamic system including the latent heat of vaporation/condensation. As 
such, it more accurately describes the energy production potential of a geothermal system that includes both hot water and steam. 
The best geothermal fields are generally found around volcanically active areas often located close to 
boundaries of tectonic plates. As shown in Figure 1.2
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, there are only a few major areas in the world 
which are rich in hydrothermal potential. Although some of the geothermal resources are located in 
populated, easily accessible areas, many others are found deep on the ocean floor, in mountainous 
regions, and under glaciers or ice caps.
Furthermore, the current commercially available geothermal power technology relies upon the 
availability of hydrothermal resources—underground sources of extractible hot fluids or steam—to 
energize the power plant. Therefore, when discussing geothermal resources, this handbook maintains 
a consistent focus on high-temperature (or high-enthalpy
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) hydrothermal resources suitable for power 
generation.
Even though the greatest concentration of geothermal energy is associated with the Earth’s plate 
boundaries, some form of geothermal energy can be found in most countries; exploitation of 
geothermal systems in normal and low geothermal gradient areas for home heating has gained 
momentum during the last decade. Ground source heat pumps can be utilized almost anywhere in the 
world to produce heat from the ground near the surface, or from surface water reservoirs.
(2) Svartsengi 76,4 MW
Recharge Area
Magmatic 
Intrusion
Hot Spring 
or 
Steam Vent
Flow of Heat
(conduction)
Impermeable R
ock
(thermal conduction)
Hot
Fluids
Cold
Meteroic
Waters
Impermeable Rock
(thermal reservoir
)
Reservoir
(thermal convection
) 
Geothermal
Well