"Everything" on Electricity


Types of energy

Easily-stored energy is not transportable/usable;
end-use energy is not storable.

Energy "Form"Examples
Easily-stored Chemical: coal, oil, nat. gas, food
Gravitational: water behind a dam
Nuclear: uranium, plutonium,
    hydrogen isotopes
Easily-transported Electrical, chemical, solar(?)
End-use Kinetic: transportation, industrial
Thermal: residential, industrial,
Radiant: residential, commercial

There are more energy graphs.

Electricity Fundamentals.

Assume "charges" can be moved.

  1. Charge unit: Coulomb (C) (~1019 electrons)
  2. Voltage unit: Volt (V), esp., voltage difference.
  3. Energy 1 C across 1 V difference is 1 J energy; voltage difference drives charge flow: current.
  4. Current (I) unit: ampere or amp (A) = C/s.
  5. Resistor allows current flow under voltage difference.
  6. Georg Ohm found relation (Ohm's law):
    V = R I. Unit: Ohm (Ω) = V/A.
  7. Power dissipated in a resistor is work done in moving charge thru voltage difference; if C V is energy, then (C/s) V = I V is rate of doing work. By Ohm's law, power dissipated is
       I V = I2 R.
  8. Bad news. This dissipation heats the current-carrying wire. Transmitting electric power loses energy in heat: lower efficiency.
Units were people who became nouns.

How to create voltage difference

  1. Magnets exist (don't ask how).
  2. Faraday discovered current-carrying wire moving in a magnetic field produces voltage.
  3. Motors reverse process. Wire in magnetic field with applied voltage difference is moved.
  4. Engineers have found efficient ways to
    • wind many-wire coils; thus increasing voltage or force.
    • transform voltage from low to high. At constant power -- note: P = I V -- lower current cuts dissipation.

    Production & Distribution of Electricity


    "Reminder": EJ ~ Quad BTU
    exajoule ~ quadrillion British Thermal Units
    watt-hr (Wh) ~ 0.9 104 W-s ~ 104 J. Thus

    trillion-kilowatthours =10(12+3+4) J =10 EJ =10 Quad

    2004 Energy Flow: 104.2 Quad BTU (DOE)
    Domestic Production Imports
    CoalGasOilNucRenSubtotals PetrolOther
    22.721.811. 33.827.75.3
    Uses (99.7 Quad BTU)
    21.217.5 33.327.84.4

    Historical Electricity Data (ref: eia.gov, fig8.4, p238)

    Electric Consumption 1950-2000
    2004 Electricity Flow: 40.8 Quad BTU (DOE)

    What drives building of electric plants

    Costs drive everything.

    • Profits. Most states regulate profits as fixed percentage of costs -- due monopoly position granted utilities. With gradual deregulation, confusion reigns.

    Different use create different loads

    • Industrial use is predictable & sets base load.
    • Cyclic use, for example, due to residential and commercial uses can typically double the load at some hours.
    • Peak load, >20%, arise from peaks in daily demand and seasonal demand. Utilities may buy power from other utilities with spare capacity.

      Different sources provide different loads.

      • Base load is met by those sources whose cost is most strongly set by capital costs: nuclear and hydroelectic.
      • Cyclic load is met by sources whose costs are more strongly set by running costs: coal, gas.

      Conclusion: Peak users pay more than cyclic user who pay more than base users.

      Economy of scale is reasonable belief costs are not linear in plant size: truer for plants with larger fraction of capital costs.
      Minus is that idled large plant impacts supply more than small.

      Mix of generating facilities

      Screening curves compare the total cost of generating facility versus hours of operation.

      Total costs:

      1. Capital costs: planning, construction, fees, but also including interest amortized over estimated lifetime of facility.
      2. Operating expenses per hour: fuel, salaries, maintenance.

      1972 screening curve

      • Intercept is capital cost per installed kWh.
      • Slope is steeper for greater running costs.

      Consumption trends

      Text has plenty on trends.

      Transporting Electricity

      Two essential elements.

      1. Transformer. Two coils -- with vastly different number of turns can transform voltage from high to low or vice-versa. Neglecting any losses in the transformer:

        The conserved power
        P =
        high-volt Ihigh volt= Vlow volt> Ilow volt

      2. High-voltage Transmission line. Again assume power is conserved. Convert power plant voltage to higher voltage: 150-750 kV.
        Vplant Iplant= Vline Iline

        This substantially reduces heating loses in transmission.

        Ploss = (Iline) 2 R
        = (Pplant plant  /   Vline)2 R

        To cite this page:
        "Everything" on Electricity
        [Saturday, 20-Oct-2018 22:32:31 EDT]
        Edited by: wilkins@mps.ohio-state.edu on Wednesday, 28-Sep-2011 09:20:10 EDT