Download 1 The Origin of Geothermal Energy

Geothermal Energy
Chapter 1: The Origin of Geothermal Energy
Chapter 2: Geological Aspects and Prerequisites
Chapter 3: The Practical Application of
Geothermal Energy in Everyday Life
Chapter 4: Examples and Advantages
§ 1 The Origin of Geothermal Energy
or
how the Big Bang
heats Your Living Room
§1 The Origin of Geothermal Energy
99% of the Earth are hotter than 1,000°C !
The mayor part of the rest is still hotter than 100°C
Reasons:
1.
Agglomeration of mass: gravitational energy 
kinetic energy  thermal energy
2.
Radioactive decay  heat
3.
Liquid metal solidifies  energy contained in the movement of
molecules is transformed into heat
4.
Energy from the sun
§1 The Origin of Geothermal Energy
• Agglomeration of mass and radioactive decay create nearly 100% of the entire heat
of the earth
• Radioactive decay still going on today
• Although agglomeration of mass took place billions of years ago, its heat is still
apparent today, since earth emits only small amounts of thermal energy
• Nonetheless the aspect of the energy of the sun should not be underestimated 
Chapter 3
How does the heat of the inner of our planet reach the surface?
1.
Convection

flow of liquids (for example magma or water)
2.
Conduction

direct transmission of heat
§ 2 Geological Aspects and Prerequisites
or
where shall
we drill the hole?
§2 Geological Aspects and Prerequisites
Denotation
Depth
Description
Earth’s Crust
0 – 30km
-consisting of hard, cleft rock
-tectonic plates are part of the crust
- 200-300°C in a depth of only 3-5km
-no clear distinction between crust and core
-density: 2.5-3.0 g/cm3
Earth’s Mantle
30-2,900km
undefined
zone
30-120km
-increasing pressure and temp.  stone becomes more
malleable; yet it can rest hard and cleft until a depth of
~120km
- temperature: ~2,700°C
-convection of matter which can be compared to a lava
lamp
- liquid matter rising to the top, cooling down and flowing
down again
-hot stone rises with a velocity of ~3cm/year
-motor, which is moving the surface of the earth, that is:
responsible for the outbreak of volcanoes, movement of
tectonic plates, earthquakes, drift of continents, creation of
mountains etc.
-not clearly belonging to crust or mantle
Upper
Mantle
120-660km
-density: 3.2 - 4.5 g/cm3
transition
zone
660-700km
-divides upper and lower mantle
700-2,900km
-density: 11.2-13.6 g/cm3
Lower
Mantle
“D-Layer”,
WiechertGutenbergdiscontinuity
Outer Core
2,900-3200km -divides Lower Mantle and Outer Core
3,2005,150km
-mainly consisting of Fe and Ni
-liquid; viscosity comparable to water
-electrically conductive flowing liquid metal  magnetic
field!
Inner Core
5,1506,378km
-6,300°C, 3.5mio bar  Fe and Ni form a solid metal-ball
which is rotates
-radioactive decay  enormous heat
§2 Geological Aspects and Prerequisites
What are excellent geological conditions for the use of geothermal
energy?
 hot subterrestrial stone
 low depth
 reservoirs of hot / warm groundwater
Do we find the same temperature in a certain depth all over the world?
No! Although the temperature averagely rises with 30°C per km, this is only a very
rough estimation.
 The subterrestrial temperature strongly depends on the local geophysical
prerequisites (such as local thickness of the crust (influencing conduction),
formation of tectonic plates, groundwater and stone (influencing convection)
etc.).
 Besides there might be superimpositions of convection and conduction (Soultzsous-Forêts)
§2 Geological Aspects and Prerequisites
§2 Geological Aspects and Prerequisites
The structure of stone and its influence on conduction and convection:
pore
qcond = - λ * Δϑ / Δz
conduction
v = ( k / η) * (Δp / Δz)
convection
cleft
mattock /
chalky
qcond = conductive part of the heat flow [W/m²]
λ = heat conductivity ~ 1.0-5.6 W/(m K)
Δϑ = difference of temp.
v = velocity of flow [m/s]
k = permeability [m²] (not [W/(m*K)] )
η = viscosity [Pa*s]
Δp = difference of pressure [Pa]
Δz = thickness of stone [m]
§2 Geological Aspects and Prerequisites
The deposit of geothermal energy in the Crust of the Earth
1. Heat in the upper layers of the Crust
2. Heat in subsoil (i.e. greater depth)
deposits of low enthalpy
hydrothermal systems
deposits of high enthalpy
petrothermal systems
§2 Geological Aspects and Prerequisites
1. Heat in the upper layers of the Crust
-strongly depending on season (until a depth of ~15m), sun, rainfall and convection
of subterrestrial water
-the heat in the upper layers can usually not be used for commercial generation of electrical
energy
- the soil can be used as a source (in winter) and as buffer (in summer) of warmth
§2 Geological Aspects and Prerequisites
2.1 Heat in subsoil  deposits of high enthalpy
- usually to be found near volcanoes or borders of tectonic plates (Larderello)
-water and steam of some hundred degree Celsius in low depth
-purpose: mostly generation of electrical energy
- having been used, the steam is usually reinjected in order to perpetuate a high
subterrestrial pressure
- very high pressure in the whole circulation-system (even water of some hundred degree
is still liquid)
- the pressure is released directly at the turbine of the power station, so that the hot
water vaporized suddenly an drives it with enormous power (“flash method”)
2.2 Heat in subsoil  deposits of low enthalpy
-this is a rule when there is no volcano or any other geological “abnormality”
-for economic generation of electrical energy, temperatures of at least 100°C are
needed  necessity of deeper drills (~5,000m)
-hydrothermal and petrothermal systems
 These aspects are important for the next chapter!
§3 The Practical Application of Geothermal Energy in Everyday Life
Or
why it is also very cool
to use this hot renewable energy
§3 Application of Geothermal Energy in Everyday Life
General distinction according to purpose:
 warming private households or public institutions
 commercial generation of electrical energy
§3 Application of Geothermal Energy in Everyday Life  3.1 warming private households
1. Warming private households
Open systems:
- due to pores and
clefts, the
groundwater
cana flow
to the(“extract-hole”)
point of
-Groundwater
(~8-12°C)
is pumped
out of
fountain
withdrawal
and warmth
can betransferred

thermal energy
is gained
cold water is returned via another
fountain
(“sink-hole”)
- an exploitation
of the soil may result for example in a crystallization of
-minerals
problem:
cannot
berealized
everywhere,
legal
in the
pores
this could
seriously harm
or restrictions
even destroy the
entire system
§3 Application of Geothermal Energy in Everyday Life  3.1 warming private households
1. Warming private households
Closed systems:
-The
area of the
ground whichoris vertically
used to gain the warmth should have 1.5 – 2
-Installed
horizontally
times the size of the area which is warmed
-System of pipes filled with transmission medium (for example
-Power: 10 – 35 W/m²
water with antifreeze
compound) or working fluid (for example
-Slinky-collector
 saves space!
-Probes:
of at least 100 meters (usually deeper)
ammonia- depth
or propane)
- Ucontact
– shape orbetween
coaxial principle
- no direct
transmission medium respectively
- material: high-density polyethylene
working -fluid
and
power:
20 ground
– 70 W/m
§3 Application of Geothermal Energy in Everyday Life  3.1 warming private households
Open and closed systems work according to the same
principle:
1. Geothermal source of warmth provides energy
2. Heat pump makes this energy useable
But how does a heat pump work?
4 steps:
1. Evaporation of a cooling liquid
2. Compression of the steam
3. Condensation of the steam
4. Relaxation of the steam
§3 Application of Geothermal Energy in Everyday Life  3.1 warming private households
§3 Application of Geothermal Energy in Everyday Life  3.1 warming private households
Arrangement can also be used to cool your house in summer:
1. Direct cooling: water in the pipes of the heating system inside the
house is pumped into the pipes in the ground
2. Indirect cooling: heat pump used as a refrigerating
machine  pipes of the heating system inside the house
are connected to the evaporator of the heat pump; pipes
under the surface outside the house are connected to the
condenser of the heat pump
 soil used as a buffer for thermal energy instead of source
§3 Application of Geothermal Energy in Everyday Life  3.2 commercial generation of electrical energy
Commercial generation of electrical energy
To work profitable, only deposits in subsoil (i.e. great depth) are
considered
High enthalpy
Low enthalpy
Excellent prerequisites
(Larderello, Italy; The Geysers,
California), due to extraordinary
geological conditions
 water and steam of some
hundred degrees in low depth
•Hydrothermal system
•Petrothermal system
No geological extraordinary
Thanks to new methods like “HDR”
commercially usable
§3 Application of Geothermal Energy in Everyday Life  3.2 commercial generation of electrical energy
Hot – Dry – Rock: A modern and promising method
-Two holes are drilled until a depth of ~ 5,000
meters
-Temperature: 200-300°C
-Water is pumped down through the first hole at
very high pressure (150 bar)  natural crevices
in the stone are widened and / or new ones are
formed (wide: up to 1mm)
-Water flows through the stone (Vol. ~ 3-10km³)
and is heated up
-Water rises to the top through the second drill
-The high pressure and temperature of the
water are transformed into electrical energy by
a turbine on the surface
Sub terrestrial stone used as a heat
exchanger
 major parts of the arrangement hidden under
the surface
§ 4 Examples and Advantages
or
let’s protect the
Flowers and save some Money
§4 Examples and Advantages
Advantages
• Geothermal energy belongs to the generation of renewable and nonpolluting
sources of energy
•No garbage
•No emission of Carbon dioxide  no greenhouse effect
•Independent of seasons and weather (in contrast to most of the other renewable
energies)
•Available nearly everywhere
•Nearly no risks
•Independence of expensive fossil fuels which are often located in politically instable
regions
§4 Examples and Advantages
Examples
-Larderello:
-oldest geothermal power station in the world (1913)
-Power: 400 MW
-Reinjection of hot steam in order to perpetuate high
subterrestrial pressure
§4 Examples and Advantages
The Geysers, California:
-Most powerful geothermal power station
-Power: 700 MW
-Comparison: nuclear power stations averagely got
between 400 and 1,400 MW at their disposal
§4 Examples and Advantages
Soultz-Sous-Forêts,
Alsace, France:
-Pilot project (for HDR)
-Power: only 6MW
-Depth: ~ 3,500 meters
-Temperature of steam: 170°C
-Flow: 40 l/s
-Expected: depth of 5,000m,
250°C, 50-100 l/s
Thanks for your attention!
•“Energie aus Erdwärme”, Spektrum Verlag, Kaltschmitt, Huenges, Wolff
•http://www.planet-wissen.de
•http://de.wikipedia.org/wiki/Erdw%C3%A4rme
•http://www.erdwaerme-lehrpfad.com/
•“Physik-Journal”, November 2008