Electricity: basics, units, sources, etc.


  1. Most electricity is made
    using (steam)-motor-generator sets
    See pix on the right:
  2. Nuclear and Hyroelectric supply base load; Coal and Wind supply cyclic load with Gas able to supply any load, including peak loads.
  3. What plants get built depend on future load expected in combination with both construction and fuel costs. Predicting future is challenging for power companies trying to run a profit.

“Review" of energy and power

Electricity Note: italic for math symbol, roman for units)

  1. Voltage (V) unit: Volt (V), esp., voltage difference.
  2. Current (I) unit: ampere or amp (A)
  3. Resistor (R) Empirically voltage across a resistor is proportional to current. V = R I
        unit of resistance is ohm: Ω = V/A.
  4. Power dissipated in a resistor by voltage driving current : P = V I = R I2 = V2/R.
  5. Bad news. Power dissipation heats resistor; Transmitting electric power loses energy in heat.

How to create voltage difference

  1. Permanent Magnets exist (don't ask how).
  2. Faraday discovered (i) current-carrying wire moving in a magnetic field produces voltage. Conversely, (ii) driving a current thru a wire in a magnetic fields moves the wire perpendicular to both current flow and magnetic field.
  3. Applications using permanent magnets: (i) electricity source and (ii) motors. Steam drives a turbine turning in array of permanent magnetics.
  4. Engineers have found efficient ways to

Electricity Sources

Comparing generating capacity to net generation requires unit conversion.
Generating capacity is displayed MW (megawatts) with entries in hundred thousands, so I use GW.
Net generation is in MkWh (mega kilowatt-hour) with entries in hundred thousand (again!), so I use TWh.

To predict the theoretical capacity, power sources runs the whole year -- 8766 hr/yr.

 Capacity1 “Predicted"
Actual Production2 Effective Use
Below: only non-generator source
[1] ? 2010 www.eia.gov/electricity/annual/pdf/table1.2.pdf
[2] 2015 www.eia.gov/totalenergy/data/monthly/pdf/sec7_5.pdf

Summary: Nuclear produces 20% of the electricity with great efficiency, Hydroelectric is about 8%; wind 3%. Coal and Gas are the the rest.

Question: While TWh is energy it is not commonly used by physicists. How do you convert TWh to EJ (for example)?

Useful knowledge. BTU the British Thermal Unit can expressed in SI. A BTU is about 1 kJ. A quadrillion BTU (1015 BTU) is called a quad. Roughly Quad is EJ, so often they are used interchangeably.
N.B.Peta W hr = Quadrillion W hr = 3.4 Quad.

What drives building of electric plants

Costs drive everything.

Different use create different loads

Different sources provide different loads.

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: (2006)

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

Other considerations affect relative use of energy sources.

Some of you may be interested in how changes occur. 1950-2010 use of coal, natural gas, and petroleum

1. "Generation" of what?
2. For what country? How would China curve look?

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, commercial
Radiant: residential, commercial

There are more energy graphs.

In writing essay on next 100 years, should face the real world, but we don't expect miracles.

To cite this page:
Electricity: basics, units, sources, etc.
[Sunday, 17-Dec-2017 18:26:43 EST]
Edited by: barrett@mps.ohio-state.edu on Wednesday, 30-Aug-2017 14:36:05 EDT