Electricity: basics, units, sources, etc.
Most electricity is made
using (steam)-motor-generator sets
See pix on the right:
- Nuclear and Hyroelectric supply base load; Coal and Wind
supply cyclic load with Gas able to supply any load, including
- 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
- Energy is the ability to do work. Unit: joule (J)
- Power is the rate of doing work or use of
Unit: watt (W) = joule/sec (J/s).
- Connection between energy and power: energy refers to any source of
usable power (to do work). Course unit examples: kWh (kilowatt-hour), EJ (exajoule)
- In physics, often assumed energy is conserved. (Efficiency is real
- Real world and thermodynamics, difficult to conserve energy.
Electricity Note: italic for math symbol, roman for units)
- Voltage (V) unit: Volt (V), esp., voltage difference.
- Current (I) unit: ampere or amp (A)
- Resistor (R)
Empirically voltage across a resistor is proportional to current. V = R I
unit of resistance is ohm: Ω = V/A.
- Power dissipated in a resistor by voltage driving
current : P = V I = R I2 = V2/R.
- Bad news.
Power dissipation heats resistor;
Transmitting electric power loses energy in heat.
How to create voltage difference
- Permanent Magnets exist (don't ask how).
- 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.
- Applications using permanent magnets: (i)
electricity source and (ii) motors. Steam drives a turbine turning
in array of permanent magnetics.
- 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.
- Most sources of electricity use electromagnetic induction. Common
variant has a stationary structure providing a constant magnetic field
-- usually a stationary array of permanent magnetic-- and rotor with
multiple current windings. Rotor driven mechanically often by steam
turbine. While it can produce dc current; nowadays a three phase ac
current is produced. It voltage can be adjusted by transformer to
decrease resistance loss.
Comparing generating capacity to net generation requires unit
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 --
| ||Capacity1 ||“Predicted"|
|Actual Production2 ||Effective Use||Source/Units||GW||TWh||TWh
|Below: only non-generator source|
? 2010 www.eia.gov/electricity/annual/pdf/table1.2.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.
- 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 hydroelectric.
- 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: (2006)
- Itercept=Capital costs: planning, construction, fees, but also
including interest amortized over estimated lifetime of facility.
- 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.
1. "Generation" of what?
2. For what country? How would China curve
Types of energy
Easily-stored energy is not
transportable/usable; 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, 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: email@example.com on
Wednesday, 30-Aug-2017 14:36:05 EDT