Energy & Its Impact on Global Society

1. Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

2. Chapter 10: Electricity & Circuits • Overview of Electric Utility Industry • Basic Electricity Principles • Batteries & Electric Vehicles • Ohm’s Law • Electrical Power: Saving Money

3. Overview of Electric Utility Industry • Electric generation responsible for one-third of all greenhouse gas emissions • Electricity consumption has largest growth rate of any major energy sector • 40% energy resources in US used to produce electricity (45% electricity comes from coal)

4. Overview of Electric Utility Industry • Before 1970s • Electric Utility Industry made up of large companies with little or no competition • Since 1970s • Marketplace is now deregulated; customers can buy electrical power from multiple vendors depending on location

5. Overview of Electric Utility Industry • Public Utility Regulatory Policies Act (PURPA) of 1978 • Opened the door to limited competition in generation of electricity • 25 – 40% total electric bill (generation electricity)

6. Overview of Electric Utility Industry • Energy Policy Act of 1996 • Opened the door for transmission lines to be used by multiple companies to transmit electricity without having to pay “home company” extra fees to use

7. Overview of Electric Utility Industry • Renewable Energy Portfolio Standards • Require a certain percentage of generated electricity (10-20%) must be from renewable sources by a certain date

8. Overview of Electric Utility Industry • Other Approaches • Feed-In Tarriffrequires energy suppliers to buy electricity produced from renewables at fixed price • Net Metering rewards customers by paying them money for electricity (wind, solar) generated in excess of demand

9. Basic Electricity Principles • Electrical charges are (+) or (-) • Like charges repel; unlike charges attract • Unit of charge is coulomb (C) with electron has (-) charge and proton has (+) charge • All atoms are neutral (no charge) • Law Conservation of Charge

10. Basic Electricity Principles • Conductors are good conductors of heat and electricity • Insulators are poor conductors of heat and electricity

11. Basic Electricity Principles • Flow of electrons in a conductor is termed electrical current • Defined as amount of charge that flows past a given point per unit time • Measured in Amperes (Amps) • 1 Ampere = 1 Coulomb/sec

12. Basic Electricity Principles • Electrical potential defined as work per charge that must be done to move charge from point to point. • Measured in Volts (V) • 1 V = 1 Joule / 1 Coulomb

13. Basic Electricity Principles • For a current to exist between two points, there must be a potential difference between those points (battery) and a path between those points through which the charges can flow. • This is a circuit.

14. Basic Electricity Principles • Two types of electrical current • Direct Current (DC) – current flows in only one direction • Alternating Current (AC) – current changes from one direction to another continuously

15. Batteries & Electric Vehicles • Battery functions like a “pump” exerting force on electrons in a wire. • Transform chemical energy into electrical energy • Two electrodes, electrolyte (chemical solution), power source

16. Batteries & Electric Vehicles

17. Batteries & Electric Vehicles • Battery has been called the most reliable source of power known. • Convenient, Portable, Reliable

18. Batteries & Electric Vehicles • Powering Automobiles: Electric Only • Electric powered cars around since 1914 • Big, bulky, low distance range (60 miles), lack passing power, long recharge time (6 – 8 hours) • Very expensive to purchase & maintain

19. Batteries & Electric Vehicles • Hybrid Cars • Use electric powered motor & gasoline engine • City driving (<25 mph) electric power • Gasoline engine kicks in for speeds >25 mph (necessary for highway driving)

20. Batteries & Electric Vehicles • Hybrid Cars • Advantages: No external recharging of batteries; this is done while car is decelerating & braking. • High fuel efficiency (40-50 mpg) • Up to 65% less emissions versus gasoline engines

21. Batteries & Electric Vehicles • Plug-In Electric Car • Hybrid car that runs only on its electric motor. • Once battery charge drops too low, gasoline engine comes on to recharge batteries during travel.

22. Batteries & Electric Vehicles • Plug-In Electric Car • 300 mile distance range • 93 mpg (electric) & 60 mpg overall • Recharge using standard 120-V outlet in 10 hours

23. Ohm’s Law • An electrical circuit exists when one has a voltage source and a continuous path through which charge can flow • Electrical resistance (R) of circuit element is property of type of material & its size (length and diameter)

24. Ohm’s Law • Electrical quantities resistance, potential difference, and current are related by Ohm’s Law • V = IR • Law works for both AC and DC

25. Elementary Circuits • A simple electrical circuit uses a source of potential difference connected by wires to different devices (called the load) to convert electrical energy to other forms of energy • Devices have their own resistances that are combined in a circuit either in series or parallel

26. Elementary Circuits • Devices in series have same current flowing through each one • Rtotal = R1 + R2 + R3 • Not practical for a house; if one appliance fails, all devices stop.

27. Elementary Circuits • Devices in parallel operate independently of one another • Preferred configuration for a house. If one appliance quits working, it does not affect the others

28. Elementary Circuits • Total Resistance (RT) is calculated using the following equation

29. Example Problem 10.2 • A 12-ohm resistor and a 24-ohm resistor are connected in series across a 12-volt battery. What is the current in the circuit? • Ans. 0.33 A

30. Example Problem 10.3 • A 12-ohm resistor and a 24-ohm resistor are connected in parallel across a 12-volt battery. What is the current in each resistor and the total current leaving the source? • Ans. 1.0 A; 0.5 A; 1.5 A

31. Electrical Power: Saving Money • Electrical Power delivered = Volts x Current • P = VI • Units are Watts 1 W = 1 V x 1 A

32. Example Problem 10.4 • An electric iron has a resistance of 18 ohms and is connected to a 120-V wall socket. What is the power consumed by the iron? • Ans. 804 W

33. Electrical Power: Saving Money • Rate Energy dissipated as Heat is proportional to current x resistance squared • P = I x R2

34. Electrical Power: Saving Money • Computation of Electrical Energy Costs • We pay for energy used; not power delivered • Units are kWh; (Power x time) • Table 10.2 (Residential Appliance Usage)

35. Electrical Power: Saving Money • Energy Conservation: Recall Midterm Project • Buy Energy Star Appliances • (10-15% home energy bill) • Change to Compact Fluorescent Lights (CFLs) • More energy efficient than incandescent bulbs • Higher front end cost; pays for itself < 6 months

36. Electrical Power: Saving Money • Energy Conservation: Recall Midterm Project • Light-emitting diodes (LEDs) • More durable and efficient than CFLs, but are more costly

37. Electrical Power: Saving Money • The Future: • Fuel Cells • Unique power converter that is efficient, non-polluting, and flexible • Clean, highly reliable, and has higher overall efficiency (40-60%) • High cost ($4000-4500 / kW); unknowns about lifetimes

38. Problems • 8, 9, 11, 14