Earth 344, Summer 2015

Overview What is energy? – Types of energy What is power? What is electricity? – Basics of electricity generation – Electricity units U.S. energy consumption

What is energy? capacity to do work Force (F = ma) acting over a distance (d) Energy = mass x acceleration x distance

2 types of mechanical energy kinetic (1/2 m v 2 ) potential (m g h) – both have units of Joules: joule = (kg) x (m/sec 2 ) x (m) where m = mass (in g) v = velocity (m/s) g = gravitational acceleration (9.8 m/s 2 ) h = height (m)

Converting from potential energy to kinetic energy Example h = 5 m What is velocity? mgh = ½ mv 2 (assuming no friction or air drag) 10 m/s x 5m x 2 = v 2 v = ? h

...and in a hydroelectric power plant? h water flow-through: mass x gravity / time (kg) x (m/s 2 ) x (1/s) x m = J/s = W = power!

Joule’s Paddle Wheel Experiment (1845) 772 foot-lbs of mechanical force required to raise T of 1 lb of water 1°F (Btu) James Prescott Joule ( ) Discovery of the relationship between mechanical work and heat

Types of energy (units = J = kgm 2 /sec 2 ) 1.Kinetic – motion (1/2mv 2 ) 1.Potential – gravitational (mhG) G = gravitational acceleration (9.8 m/sec 2 )

Types of energy (units = J = kgm 2 /sec 2 ) 1.Kinetic – motion (1/2mv 2 ) 1.Potential – gravitational (mhG) G = gravitational acceleration (9.8 m/sec 2 ) Greatest potential energy & lowest kinetic energy h

Other types of energy (units = J = kg m 2 /sec 2 ) Thermal calorie = energy to raise T of 1 g of water by 1°C Btu = energy to raise T of 1 lb of water by 1°F 1 cal = J; 1 Btu = 1,055 J H 2 O solid J/g  H 2 O liquid H 2 O liquid + 2,260 J/g  H 2 O gas

Chemical CH O 2 = 2 H 2 O + CO kJ/mol mol = 6.02 x atoms or molecules of a substance Other types of energy (units = J = kg m 2 /sec 2 )

Other types of energy Nuclear reactions 235 U + 1 n o --> fission fragments neutrons MeV* *eV = 1.6 x J Fissioning 1 kg of U 235 = ? For 1 mol (6 x particles), 1 eV = 96 kJ/mol 200 MeV = 2,000,000,000 kJ/mol

Types of energy (units = J = kgm 2 /sec 2 ) 5.Nuclear 235 U + 1 n o --> fission fragments neutrons MeV* *eV = 1.6 x J Fissioning 1 kg of U 235 = (24,000 MWh) = burning 3,000,000 kg (3,300 tons) of coal = burning 190,000 kg (190 tons) of crude oil Fissioning 1 kg of natural U in a reactor = burning 14,000 kg (14 tons) of coal = 45,000 kWh (45 MWh) = 100 tons = 30 tons

Energy conversion & the laws of thermodynamics #1: Energy cannot be created or destroyed, but it is subject to change from one form to another. #2: In any energy transformation, some of the original energy is always lost as heat (entropy).

Energy Conversion

Energy conversion in power plant Heat source: Chemical E -(fossil fuel) Nuclear E -(Enriched UO 2 ) Sunlight Produces thermal energy Kinetic E of steam Kinetic E of turbine Electrical E into grid

What is power? amount of work performed per unit time (or the rate of energy use) Energy per unit time = J/sec = watt (W) 1 kW = 3.6 x 10 6 joules per hour Power x time = Total energy used (kilo-Watt-hour) kWh

How much is a Watt (W)? 1 watt: typical lightbulb ( W) 1 kW (10 3 W) = an electric heater (1 kW) or small car engine ( kW) 1 kW-hr* = 3.60 x 10 6 joules *the amount of energy that will keep an electrical heater running for one hour

How is a Watt connected to electrical units? Voltage: energy / charge (V = J/C) Volt [V] Current: charge (flow) / time (A = C/s) Ampere (amps) [I] Multiply Voltage × current = J/C ×C/s = J/s = W (Watt)

River – current analogy Lots of “voltage” (relief) Little current Lots of “current” (flow) Little “voltage” (relief)

River – current analogy Lots of “voltage” (relief) Lots of current Make use of it

Relative Power: Typical Light Bulb = W Electric Heater = 1 kW Stove = 12 kW Lightning Strike = 1 MW (10 6 W) Typical Wind Turbine = 1.5 MW Avg. Coal Power Plant = 600 MW Nuclear Reactor = 1 GW (10 9 W) Annual Global Electricity Use = 1 PWh (10 15 Wh) Annual Global Energy Use = 150 PWh Enough to power 300 U.S. homes!

What is electricity? movement of electrons between atoms in a current insulators versus conductors Wood, Glass, TeflonMetals, Graphite

Michael Faraday: Electromagnetic Induction (1831) rotation of a wire within a magnetic field produces a current of electricity

Magnetic fields and currents According to the right-hand rule, the electron current in a wire and the magnetic field it generates are perpendicular to each other.

Generators long shaft with coiled copper wire inside a giant magnet turbine spins shaft (using kinetic, chemical, nuclear energy, etc) electric current induced in wire

Units of electricity I = V/R current (I) = charge through a given area per unit time (amps = Q/sec) voltage (V) = “pressure” or energy of each charge (volts = J/Q) resistance (R) = resistance to flow of current (ohms)

QUIZ TIME! How is electrical power calculated from I and V? (Remember: power = energy per unit time, W)

QUIZ TIME! How is electrical power calculated from I and V? Power (W) = Current x Voltage = I x V W = (Q/sec) x (J/Q) = J/sec

QUIZ TIME! U.S. household outlets are 120V. If you plug in a 60W light bulb, what is the current drawn by the light bulb?

QUIZ TIME! U.S. household outlets are 120V. If you plug in a 60W light bulb, what is the current drawn by the light bulb? P = IV I = P/V I = 60W/120V = 0.5 amps of current

Units of electricity

The kilowatt hour Equal to 1,000 watt-hours or 3.6 megajoules – If used at constant rate, equal to power*time Basically, how much energy you use and get charged for by DTE In 2013, average annual use of 10,908 kWh per person (U.S. eia)

Example 60W / 120V = 0.5 amps = current drawn 60W * 24 hours = 1440 Wh = 1.4kWh 0.06 kW * 24hr * $0.143/kWh = $0.20

Electricity Transmission

Alternating Current (AC) Direction of current alternates/reverses (hertz) – 60 times/second in U.S. – 50 times/second in Europe = most power from the plant Direct Current (DC) Direction of flow is always the same Positive/negative; +/- Examples: batteries, fuel cells, solar cells

Why does our grid use AC? 1.Generators produce AC (would need to convert to DC) 2.Transformers need AC 3.Easy to convert DC to AC, but AC to DC is expensive 4.Easier to transmit AC over long distances

Electricity Transmission Energy losses lowest at high voltage, low current, DC (but most of grid is AC)

Coal = 100 units. After losses of 98 units (mainly heat, friction), only 2 units used to produce light.

U.S. Electricity Grid

U.S. EIA Annual Review (2011) U.S. Electricity U.S. annual electricity consumption = 4138 TWh

U.S. EIA Annual Review (2011) U.S. Electricity U.S. annual electricity consumption = 4138 TWh What else do we use energy for?

Global Electricity U.S. EIA U.S. China Europe India Total annual = ~21,000 TWh Expected to double from 2000 to 2030

U.S. EIA Annual Review (2011) U.S. Energy ProductionConsumption

Global Energy World Energy Outlook (2011) Mtoe = million tons of oil equivalent