Energy Conversion Efficiencies

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Energy Conversion Efficiencies
Converted energy form
Initial energy form
Electric
Thermal
Kinetic
Chemical
Radiant
Brake drum 100
Generator 95-99
Kinetic
Water turbine 86
Gravitational
Electric motor 65-93
Storage battery 72
Heating coil 100
Lamp incandescant 5-8 flourescent 25-30
Electric
Solar furnace 100
Solar cell 15-27
Photosynthesis 0.6
Radiant
Furnace of steam boiler 85-88
Dry cell battery 91
Chemical
Muscle 45
Steam turbine 40-47
Thermal
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Assessing energy system efficiencies
Conversion Network (including extraction,
storage, transmission)
Primary Energy Source
Final Energy Form
Required Energy Service
Primary Energy Carrier
Nuclear Geothermal Tidal Solar
Kinetic Heat Electricity Radiation
Physical work Transportation Cooking Heating Cooli
ng ICT Entertainment
Nuclear fuels Geothermal heat Tidal flow Solar
radiation Fossil fuels Biomass Hydrological
cycle Wind Waves and currents
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Assessing energy system efficiencies
Example Residential lighting (from fossil fuel
based electricity production)
Primary Energy Carrier
Conversion device
Conversion device
Conversion device
Useful output
Extraction Refining Transport
Boiler (chemical to thermal)
Turbine (thermal tomechanical)
Generator (mechanicalto electrical)
Electricity
Chemicalenergy In fuel
Conversion Efficiencies 0.9 x
0.88 x 0.43 x
0.98 0.33
Transmission
Lamp
Light
Electricity
Conversion Efficiencies 0.33
x 0.93 x 0.08
0.025
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Assessing energy system efficiencies
Example 1 Residential lighting (from fossil fuel
based electricity production)

• The total system conversion efficiency is 2.5
  (fossil fuel into visible light).
• The conversion efficiency for fossil fuel based
  residential electricity is about 31.
• Every MJ of residential electricity thus
  requires 3.23 MJ from fossil fuel.
• During 24 hours a 100W bulb requires 8.64 MJ of
  electricity (final energy form).
• The 100W light bulb therefore requires 28 MJ
  stored in fossil fuel (primary energy).
• This roughly equivalent to 1.1kg of hard coal
  (net calorific value 25MJ/kg).

Example 2 Power supply without load (connected
to coal based electricity)

• Every MJ of residential electricity requires
  3.23 MJ from fossil fuel.
• Most current power supplies use about 2W when
  connected without load.
• There are currently over 3 billion power
  supplies in operation in the US.
• Lets assume that 10 of all power supplies are
  connected all the time.
• Lets assume that these power supplies are
  without load 80 of the time.
• Question How much hard coal is needed per year
  to generate the required energy?

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Assessing energy system efficiencies Case study
Fuel cell vehicle
Main issue with hydrogen It is an energy
carrier not an energy source,
which means that it
has to be generated first. Another issue with
hydrogen It has high gross calorific value (142
MJ / kg),
but very low energy to volume ratio
(1/4
that of petroleum, 1/3 that of natural gas).
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Assessing energy system efficiencies Case study
Fuel cell vehicle
1) Hydrogen is generated by a reformer
2) Fuel cell converts hydrogen into
electricity 3) Electricity powers electric motor
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Assessing energy system efficiencies Case study
Fuel cell vehicle
Heat
H2O2
CO2
Heat
Heat
Heat
Electrical energy
Mechanical energy
Reformer
Fuel cell
Electricmotor
H2
Pressure
H source
Conversion Efficiency 0.6 0.85 x
0.5 0.6 x 0.8
0.24 0.41
Missing Hydrogen compression 0.9 Regenerative
braking 1.1
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Assessing energy system efficiencies Case study
Fuel cell vehicle
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Assessing energy system efficiencies Case study
Fuel cell vehicle
Electric vehicle (well-to-wheel efficiency,
electricity from fossil fuel)
Power plant
Battery
Electricmotor
Transmission
0.33 0.55 x 0.93 x
0.8 x 0.8
0.2 0.33
Electric vehicle (electricity from solar energy)
Battery
Electricmotor
Transmission
0.93 x 0.8 x
0.8 0.6
Fuel cell vehicle (hydrogen from electrolysis,
electricity from solar energy)
Fuel cell
Electricmotor
Transmission
Compression
0.9 x 0.86 x
0.5 x 0.8
0.31
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Reading for Wednesday, 3 AprilChapter 2 in
Energy Science, Policy and the Pursuit of
SustainabilityFuture World Energy Needs and
ResourcesChapter 5 from L R Radovic Energy
and Fuels in SocietyEnergy Supply and Demand
pdf of second reading available on course
website http//www.bren.ucsb.edu/academics/course
.asp?number288