The Physics of Energy sources
Energy conversion scheme in a typical power plant
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Ref 1: Boyle, Everett and Ramage, Energy Systems and Sustainability (2003)
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General energy conversion scheme
Common to any plant using fuel (Oil, Coal, Biomass, Nuclear)
From chemical to
thermal energy
Common to any plant using mechanical energy
(Hydraulic, wind farm…)
From thermal to kinetic
Or directly kinetic
From kinetic
to electrical
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Energy production – a typical power plant
From thermal
to kinetic
Ref to Watt s
steam engine and
Carnot s law
From kinetic to electrical
 Faraday s law
From chemical
to thermal
energy:
Combustion
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Ref 1
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From Thermal to Mechanical energy
Carnot cycle: a quick explanation
!   The Carnot cycle (proposed in 1824) is an ideal thermodynamic
cycle which can be used to model a heat engine.
!   A heat engine transfers energy from a warm region (TH) to a cool
region (TC).
For an ideal heat engine, the efficiency is given by:
TC
W
η = = 1−
Q
TH
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Efficiency
0.9
Tc=300K
Tc=273K
0.8
0.7
0.6
TC
W
η = = 1−
Q
TH
0.5
0.4
0.3
0.2
0.1
0
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Even so (for an ideal system) if for example TH=600K and TC=300K η=0.5
In this case, the maximum efficiency is 50%
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Faraday s law: use of a Magnetic Field
A magnetic field can be induced by moving charges
Current I due to electrons
moving in a wire
Induced B field
Magnetic field act on moving charges:
If a charge q is moving within a magnetic field B, a force (Lorentz) will apply on the charge
B
F
q

 
F = qv × B
v
 Faraday s experiment
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Faraday s experiment
Generator (or dynamo or alternator) is based on
Faraday s law
A magnet moving respectively to a coil of wire
will induce a current through this wire (induction)
 Refer to 2nd year EM course
Faraday s experiment
Electromagnetic induction
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Application: The generator
By connecting the turbine to
the coil (or the magnet) the
rotation will induce a current
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Energy conversion efficiency
!   Primary energy: raw energy that is generated by the fuel
combustion or the heat from nuclear fission…
!   However before combustion we need to extract, process and
transport the fuel
!   This will require some energy: it is about 2.5% of the primary energy which
is lost in these processes
!   Primary energy is then converted into deliverable energy
!   CombustionHeatKineticElectric energy
!   The losses cause an efficiency of about 30 to 40% (~35%)
!   So at the exit of the power plant we get ~ 34% of the primary
energy (deliverable)
!   Most of the losses will be dissipated through heat
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