1. Energy: Concepts and Examples SHORT VERSION – may look weird Steve Colt Envi 201 University of Alaska Anchorage afsgc@uaa.alaska.edu Version 1: 16 Feb 2004

2. 2 Energy: What is It? Ability to do Work –(formal physics definition) Food  We can move, think, live Warmth or Heat, Coolness Light Sound (speaker) Motion (transportation) Mechanical Power (skilsaw)

3. 3 What Forms does it Take? Chemical –Bagel, gasoline Heat –Warm room, hot water Mass (E=Mc 2 ) –Sun, nuclear bomb, nuclear reactor

4. 4 Forms of Energy Kinetic – energy of motion –Speeding bicycle Potential – energy of position –Bicycle at top of hill

5. 5 Forms of Energy Electric Energy (Charge) –Charged Battery Electromagnetic Radiation –Visible Light, microwaves

6. 6 Measuring Energy – Common Units Joule – metric unit (not very useful) –1 bagel has 1.2 million joules of food energy Btu – British thermal unit –1 lb water up by 1 degree f kWh – kilowatt hour –Used for electricity – 1 kWh costs 10 cents in Anchorage

7. 7 Power: the Rate of Energy Use –Just as speed = distance per time, Power = Energy conversion per unit of time Measured as Watts (W) –60-watt light bulb converts electricity to light (and heat!)… –While it is on! –Technically, 1W = one joule per second

8. 8 Power: Examples Human (at rest) –About 100 W (we are always on!) Small candle –About 1 W (when it is lit!) Hair dryer –1,000 W = 1 kilowatt = 1 kW –If it is on for one hour it uses: –1 kW x 1 hour = 1 kilowatt-hour (1 kWh) –(costs 10 cents)

9. 9 Power: Horse vs. Hairdryer 1 Horsepower =.67 kW = 670 watts –Invented by James Watt so he could charge for steam power in a way people could understand –Few horses can actually produce 1 hp –Hairdryer, using 1 kilowatt, = 1.3 horsepower

10. 10 Conversion Example: Jet Engine Forms: Chemical -> Heat -> Motion Power output: 15 Megawatts during take-off, Much less during cruise Picture of jet engine

11. 11 Energy Flow in Natural Systems

12. 12 Solar Radiation Received at Earth’s Surface: average is about 150 watts per square meter

13. 13 Conversion of Solar to Plant Biomass Only about 1-5% of solar radiation is converted to chemical energy of plant matter

14. 14 Conversion of Plants to Animals Trophic Level = feeding level Plants (autotrophs = self-feeders) Herbivores –Convert 1-10% of plant energy to biomass Carnivores –Convert 1-10% of herbivore energy to their own biomass 16 lbs of corn = 1 pound of beef

15. 15 Two Laws of Thermodynamics First Law: –Energy is converted from one form to another Second Law: –Energy is degraded with every conversion, and ends up as low-grade heat Example: Your Toaster –…Electricity->Heat->(toast + warmth)

16. 16 Implication: Energy conversions are never 100% efficient There is waste heat lost at every step Efficiency Varies Dramatically…

17. 17 Efficiency of Energy Conversion

18. 18 Pre-Industrial Energy Sources Source: Smil 1994

19. 19 Energy Use per Person Source: Smil 1994

20. 20 Energy Use per Person The U.S. converts energy at the constant rate of about 10 kW per person This is like having 100 “energy slaves” working full-time for every american child and adult person

21. 21 Energy Use vs. Human Development The Human Development Index combines life expectancy, education, and income into an index that ranges from zero to 1

22. 22 Impacts: Sulfur and Nitrogen

23. 23 Impacts: Land Use from Production

24. 24 Changing Energy Efficiency Light Bulbs Jet Engines

25. 25 Overall, we seem to be getting more efficient….. This is the “T” factor – how much energy per dollar of economic output

26. 26 But World energy use still grows by 1-2%/yr

27. 27 References Smil, Vaclav. 1994 Energy in World History. Westview. Smil, Vaclav. 2003. Energy at the Crossroads. MIT Press. Scott Brennan and Jay Withgott. 2003. Environment: The Science Behind the Stories. Pearson/Cummings. BP Statistical Review of World Energy. 2003.