"Everything" on Electricity
- Energy is the ability to do work. Unit: joule (J)
- Work is product of distance and component
of force along the distance moved. Unit: joule (J).
- Power is the rate of doing work or use of energy.
Unit: watt (W) = joule/sec (J/s).
- Energy Conserved: energy is conserved.
Difficulty is conserving useful
- Efficiency is the measure of our success in
converting stored energy into useful energy: .
Types of energy
Easily-stored energy is not
end-use energy is not storable.
||Chemical: coal, oil, nat. gas, food
Gravitational: water behind a dam
Nuclear: uranium, plutonium,
||Electrical, chemical, solar(?)|
||Kinetic: transportation, industrial
Thermal: residential, industrial,
Radiant: residential, commercial
There are more energy graphs.
Assume "charges" can be moved.
- Charge unit: Coulomb (C)
- Voltage unit: Volt (V), esp., voltage
- Energy 1 C across 1 V difference is 1 J energy;
voltage difference drives charge flow: current.
- Current (I) unit: ampere or amp (A) = C/s.
- Resistor allows current flow under voltage
- Georg Ohm found relation (Ohm's law):
V = R I. Unit: Ohm (Ω) = V/A.
- 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 =
- Bad news.
This dissipation heats the current-carrying wire.
Transmitting electric power loses energy in heat:
Units were people who became nouns.
How to create voltage difference
- Magnets exist (don't ask how).
- Faraday discovered current-carrying wire
moving in a magnetic field produces voltage.
- Motors reverse process. Wire in magnetic field
with applied voltage difference is moved.
- 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
||=10(12+3+4) J ||=10 EJ ||=10 Quad|
2004 Energy Flow: 104.2 Quad BTU (DOE)
|Uses (99.7 Quad BTU)|
| ||21.2||17.5 ||33.3||27.8||4.4|
Historical Electricity Data (ref: eia.gov, fig8.4, p238)
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.
- Capital costs: planning, construction, fees, but also including
interest amortized over estimated lifetime of facility.
- Operating expenses per hour: fuel, salaries, maintenance.
- Intercept is capital cost per installed kWh.
- Slope is steeper for greater running costs.
Text has plenty on trends.
Two essential elements.
- 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
- High-voltage Transmission line. Again assume power is
conserved. Convert power plant voltage to higher voltage: 150-750 kV.
This substantially reduces heating loses in transmission.
2 R |
|| (Pplant plant /
To cite this page:
"Everything" on Electricity
[Sunday, 17-Dec-2017 18:09:04 EST]
Edited by: email@example.com on
Wednesday, 28-Sep-2011 09:20:10 EDT