Thermodynamics for energy statisticians

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Thermodynamics for energy statisticians

• An introductory chapter to the UN Energy
  Statistics Manual
• Suggestion provided by the Swedish Energy Agency
• Author Dr. Anders Johansson
• Presented by Mr Paul Westin

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Outline of presentation

• The task
• Energy sources and fuels
• Energy systems
• Thermodynamics
• Renewables and availability
• Outline of chapter for the Manual

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The task

• Background, settings, borderlines and conceptual
  framework
• e) Basic presentation of the Laws of
  thermodynamics. The aim is to increase the
  knowledge among energy statisticians on what
  physical laws apply for energy.

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Fuels and sources

• Theres really a small number of basic energy
  sources
• Fossil fuels, peat and bioenergy originate from
  photosynthesis processes, i.e. converted solar
  energy
• Hydro, wind and wave energy also mainly originate
  from solar energy (weather), tidal energy from
  gravity/motion
• Uranium (like essentially all matter) really
  originate from exploding supernovas
• True geothermal energy originate from radioactive
  decay and the Earths internal heat.
• Ambient heat is stored solar heat, and renewable.

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Energy source and energy carrier

• Coal is both a source and an energy carrier
• Crude oil is a source and a carrier
• Natural gas is a source and a carrier
• Refined oil products are energy carriers
• Electricity, district heat are energy carriers
• Hydrogen has to be produced and is thus an energy
  carrier.

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The steam engine came first!
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Thermodynamics

• The steam engine was invented first and the
  scientific understanding of the processes
  involved followed.
• Thermodynamics is however considered a basic
  scientific/engineering subject (a branch of
  physics)
• For energy statistics purposes, a classical
  (engineering) thermodynamic approach is most
  relevant.
• The laws of thermodynamics are axiomatic (at
  least they have yet to be disproved!)
• The laws of thermodynamics show that
• perpetual motion is impossible
• energy conversion is always associated with
  losses
• energy is however always conserved in total

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Energy units

• Energy is measured in Joule,
• Mechanical work often in Nm.
• Electricity is mostly measured in kWh
• Other units often used are e.g. mtoe, and BTU, cf
• Conversions always lead to a risk for confusion
  and errors.
• Preferably SI-units should be used.

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Power units

• The same goes for power.
• Preferably Watts or Joules/second should be used.
• There are other power units around, e.g.
  horsepower, Btu/hour and tons of refrigeration.

1001 hp 746.4 kW
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Systems

• A fundamental concept of thermodynamics!
• System boundary is needed for analysis
• From a thermodynamical perspective Heat and
  Work only exist at a system boundary.
• Energy statistics considers flows of fuels, other
  energy carriers, stock changes, often within and
  to and from a nation or region. (a geographical
  system boundary)

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The four laws of thermodynamics

• 0. The zeroth law is a consequence of the second
  law. Bodies in contact with each other assume the
  same temperature.
• The first law, or the energy principle, which
  says that energy cannot be destroyed, only
  converted into other forms (states)
• The second law, which says something about the
  direction of conversion of energy (implies that
  energy quality is important)
• The third law, also a consequence of the second
  law, and it says that when the temperature of a
  system is zero (K) the order of the system
  (entropy) reaches a constant value (there is no
  movement in the matter)

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The energy principle first law

• The increase in the internal energy of a
  thermodynamic system is equal to the amount of
  heat energy added to the system minus the work
  done by the system on the surroundings
• Heat and energy are equivalent, and mutually
  transferable
• Energy statistics is essentially a form of first
  law analysis, i.e. Electricity, heat, oil etc.
  are all added together in energy balances
• This type of analysis says nothing about how well
  the energy is used.

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Second law on energy quality

• If and only if there is a temperature difference
  work may be generated from heat
• Heat cannot of itself pass from a colder to a
  hotter body
• Losses are necessary to transfer heat.
• There are unavoidable losses when producing e.g.
  electricity from fuels, heat in heat pumps, etc.

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Energy quality

• The quality of energy is decreased by every
  transformation (since losses occur)
• Exergy is a term that is used to show the maximum
  work a system can produce
• Exergy depends on the available heat sink
  (temperature of surrounding)
• Energy with the exergy/quality 1.0, e.g.
  electricity may be fully converted to mechanical
  work (although with some heat losses in practice)
• Energy in heat (100C, e.g. with the quality 0.2,
  cannot be used for much more than spatial
  heating, the quality is too low to produce work.

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Availability of renewables

• Some renewables are flowing resources, and
  never-ending
• Some renewables are limited stocks (biomass),
  although re-generated if treated in a sustainable
  way.
• Sometimes problem of matching demand with supply
  of renewables (e.g. wind-power vs. Electricity
  demand)

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Outline of chapter to the Manual

• Introduction
• Energy sources, fuels and carriers
• Thermodynamics
• The four laws of thermodynamics
• On the quality of energy exergy content
• On the availability of renewable energy sources

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Thank you!

• Contact
• paul.westin_at_energimyndigheten.se
• 46-16 544 20 58
• Swedish Energy AgencyBox 310, SE-631 04
  Eskilstuna, Sweden