# Electricity: basics, units, sources, etc.

THM:

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

• Energy is the ability to do work. Unit: joule (J)
• Power is the rate of doing work or use of energy.
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 world effect.)
• Real world and thermodynamics, difficult to conserve energy.

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
• 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.

## 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" Production Actual Production2 Effective Use Source/Units GW TWh TWh Coal 340 2900 1700 58% Gas 470 3700 1000 27% Petroleum 64 540 28 5% Nuclear 110 910 790 86% Hydro 78 667 320 48% Wind 39 330 130 36% Below: only non-generator source Solar 1 9 2 23% Total 1100 9400 4100 43% [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.

## 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.

• 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.

• 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)

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.

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

### Types of energy

 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.