Page 52 - Analysis and Design of Energy Geostructures

Energy and geotechnologies 21

l. What are the three main components of geothermal energy? How does the geo-
thermal gradient vary in the shallow subsurface and which temperature values are
usually observed in temperate areas?
m. The temperature field in the subsurface, in the worst case, is sensitive to a varia-
tion of the atmospheric conditions within the first:
i. 4 6m
ii. 25 30 m
iii. 40 50 m
iv. 80 100 m
n. In general, shallow geothermal systems can be exploited:
i. To produce heat and electrical power
ii. To produce power
iii. To produce heat
iv. None of the above

Solutions
a. Energy sources can be classified based on their availability in nature as
primary and secondary energy sources. Primary energy sources represent an
energy form that has not been subjected to any conversion and is avail-
able in nature, for example fossil fuels, mineral fuels, solar energy, geo-
thermal energy, wind energy, tidal energy and biomass sources. Secondary
energy sources represent an energy form that has been transformed from
primary energy sources and is not available in nature, for example elec-
trical energy, refined fuels and synthetic fuels.
Primary energy sources can be further classified depending on
whether they can renew themselves at a sufficient rate in human time
frames. Renewable energy sources, such as solar energy, geothermal energy,
wind energy, tidal energy and biomass, can renew themselves at a suffi-
cient rate in human time frames. Nonrenewable energy sources, such as fossil
fuels and mineral fuels, cannot renew themselves at a sufficient rate in
human time frames. Based on the classification described above geother-
mal energy is a renewable primary energy source.
b. Primary energy sources are:
i. Renewable at human time frames
ii. Nonrenewable at human time frames
iii. Renewable or nonrenewable, it depends on the energy sources
iv. None of the above
c. Joule [ J], Calorie [cal], Watt-hour [Wh] and Tonne of oil equivalent
[toe].