Solar and Renewable Energies

Transcription

1 Physics 162: Solar and Renewable Energies January 7, 2010 Prof. Raghuveer Parthasarathy Winter 2010

2 Lecture 2: Announcements Reading: Wolfson, Chapter 2 Homework Due: Problem Set 1 due by 5pm. Homework: Problem Set 2. Due Thursday Jan. 14 (by 5pm) posted on the web page

3 Course Overview Last lecture note course web page: Syllabus, etc. Lecture slides will be posted. Office hours (incl. mine today 10 11am) Note clickers: participation grade, starting next week How much energy do we use? Where does it come from?

4 Last lecture Power = the rate of energy usage Power = Energy / Time Watts (W) are a unit of power Typical human power: Average US rate of energy consumption: Important numbers! A 10 W B 100 W C 1,000 W D 10,000 W E 100,000 W A 10 W B 100 W C 1,000 W D 10,000 W E 100,000 W

5 Your energy consumption history world average

6 Why use so much energy? Increased standard of living Manufacturinggoods Transport: trade, education, etc. Health, e.g. vast improvements in life expectancy [Graph] Enables a huge human population [Graph]

7 Life Expectancy (US) Men and women, from birth World avg Swaziland, still < 33 from 01.html

8 Why use so much energy? Increased standard of living Manufacturinggoods Transport: trade, education, etc. Living comfortably Health. Vast improvements in life expectancy Enables a huge human population [Graph]

9 Human Population Most of human history: pop. < 10m 1 C.E. (1 A.D.): pop. 200m 1800: 1 billion : +1/2 billion : + 1 billion 2009: 6.9 billion Projected peak about 9 billion, 2050

10 Human Population Easier to see on a logarithmic scale divisions are powers of 10. Review: What is 10 4? A. 400 B C. 10,000 D. 40,000

11 Human Population Log scale What is 10 0? A. 10 B. 1 C. 0.1 D. 0 (To see this: 10 3 = =1000; 10 2 = 10 3 /10 = 100; 10 1 = 10 2 /10 = 10; so 10 0 = 10 1 /10 = 1;)

12 Why use so much energy? Increased standard of living Manufacturinggoods Transport: trade, education, etc. Living comfortably Health Enables a huge human population

13 Why do you use so much energy? Also: Increases quality of life. ipods... travel... chocolate... (Hard to quantify.) Correlation between GDP, energy usage [graph next slide]; other measures also (e.g. Human Development Index (HDI)

14 GDP and Energy consumption Graph from Sustainable energy: without the hot air, David McKay (2009) Data from UNDP Human Development Report, 2007 Power consumption (kwh/d/person) GDP per capita ($)

15 GDP and Energy consumption Graph from Sustainable energy: without the hot air, David McKay (2009) Data from UNDP Human Development Report, 2007 Power consumption (kwh/d/person) Logarithmic scales GDP per capita ($)

16 Your energy consumption uses What is your 10 kw used for? Buildings

17 Problems with energy consumption Non sustainable rapid depletion of fuels Local environmental damage: pollution, clearing wilderness, etc. Global environmental damage atmospheric changes climate change at rapid time scales Discussed in detail in Physics 161 (Spring)

18 It s getting worse... Energy usage worldwide is increasing Climate change is an increasingly serious problem

19 US:... and it s mostly your fault 5% of the world population uses 25% of the world s energy emits 22% of the world s CO 2 You are responsible for high rates of energy consumption, resource depletion,... However, you also have the wealth, education, and political influence to do something to improve the situation!

20 We need: So what do we need? Alternative (i.e. non fossil fuel) sources of energy Reducedenergy consumption

21 Estimation There are several possible alternative energy sources. Are any at all feasible? Let s do a quick calculation about solar energy. How much is there? What is the area of Oregon? Is this something we should remember? No!! Is this something we should look up? No. We should be able to estimate things like this. How?

22 Estimation P What is the area of Oregon? E Oregon is shaped like this: I know that it takes about 2h to drive north to Portland, and 3h to drive south to California. 5 hours 60 miles / hour = 300 miles therefore Oregon is about 300 miles long North South Given its shape, it looks like Oregon is about 400 miles East West. (I ve never driven to Idaho.) Oregon s area is 120,000 square miles. (For you skeptics: the exact # is 98,500 sq. miles.)

23 Estimation The power carried by sunlight hitting our latitude is 75,000,000 Watts per square mile, i.e W / sq. mile. (This we would have to look up.) Therefore the total solar power incident on Oregon is sq. mi W / sq.mi. =... I m not going to bother multiplying it s a waste of effort. 7.5 is a bit under 10, 1.2 is a bit over 1, so Total solar power incident on Oregon = W.

24 Solar Power Estimation Total solar power incident on Oregon W. But this isn t exact! so what? The point is: is it a million W or W or W the order of magnitude tells us the scale of things! How much power do you use? (Recall) A W B W C W =10,000 W = 10 kw D W

25 Solar Power Estimation Total solar power incident on Oregon W. You use 10 4 Watts. The solar power incident on Oregon, if totally harnessed, would be enough for how many people s needs? A people (1 billion) B people / 10 4 = (i.e. subtract exponents) C people (1 thousand)

26 Reasons to be optimistic There are several possible alternative energy sources. We just calculated: solar power incident on Oregon alone could be sufficient for 1/6 of the world s population. Other alternative energy sources exist as well. (But don t get too happy...) Also, there s lots of room for improvement in energy efficiency i.e. using less energy especially with respect to buildings & transport.

27 Next... What is our present situation? What are our problems? What is energy? What are our alternatives to fossil fuel based energy? What is the underlying science? Most of the course. e.g. What is biomass? How do solar cells work? Why are batteries so important?

28 Units Quantifying physical phenomena requires a clear understanding of units Let s discuss these...

29 Measurement In the beginning... counting. (1,2,3,...) Measurement: Counting quantities relative to some standard. E.g. measuring a length of 3 feet: 3 the length of some standard defined (by convention) as one foot.

30 Units Different standards can be used for the same physical quantity E.g. feet, centimeters, parsecs for length These are units We can convert from one unit to another

31 Unit conversion We can convert from one unit to another An example: There are 1.6 kilometers per mile. Convert the distance 2 miles to kilometers [Ask]

32 Unit conversion We can convert from one unit to another An example: There are 1.6 kilometers per mile. Convert 2 miles to kilometers 2 miles 1.6 km / mile = 3.2 km Like writing 2 1 = 2, since 1.6 km = 1 mile The unwanted units cancel

33 Unit conversion Units can be treated algebraically, and only the correct calculation gives the correct units E.g. suppose we tried dividing instead of multiplying: Convert 2 miles to kilometers 2 miles (1.6 km / mile) = 2 miles (1 mile / 1.6 km) = (2/1.6) mile 2 / km Nonsensical units this can t be right!

34 Another example: Unit conversion horsepower (hp) is a unit of power. 1 hp = 750 W (actually 746, but we ll be rough) Consider a car with a 200 hp engine What is the car s power consumption, in Watts? work on this (without a calculator)... Answer: 200 hp (750 W / hp) = 150,000 W (Note 2 75 = 150, and there are 3 zeros.)

35 Units SI units meters (length), kilograms (mass), seconds (time), Joules,... a convenient set SI unit of energy: Joules (J) Other Energy units: Btu (British thermal units), calories, toe (tons of oil equivalent) (People use lots of different units for energy, so we often have to convert) (Don t bother memorizing conversion factors; I certainly don t remember how many Joules are in a Btu, e.g.)

36 Unit conversion You consume about 2000 Food calories of energy per day. There are 1000 calories per food calorie. (1 calorie = The amount of energy needed to raise the temperature of one gram of water 1 Celsius.) There are calories per Joule. How much energy do you consume per day, in Joules?

37 Which is correct? Unit conversion A. B Food calories 1000 calories/ Food calorie 1 Joules/ calorie = 8,374,000 Joules 2000 Food calories 1000 calories/ Food calorie calories / Joule = 478,000 Joules

38 Unit conversion How much energy do you consume per day, in Joules? A 2000 Food calories 1000 calories/ Food calorie 1 Joules/ calorie = 8,374,000 Joules Units can be manipulated algebraically.

39 Using scientific notation ( ) ( ) = A. 2 B. 200 C. 2,000 D E This sort of math should be familiar. Office hours are a good place to learn more!

40 Average power usage Last time we discussed the rate at which your body can produce energy i.e. your power and got a very rough intuitive feel for Watts How can we estimate your body s average power consumption, in W, based on your 2000 Food calorie input? [Ask]

41 Power, Energy, and Time How are power, energy, and time related? A. Power = Energy / Time B. Energy = Power / Time C. Power = Energy + Time D. Time = Power Energy

42 Average power usage Power = Energy / Time. SI Units: 1 Watt = 1 Joule / Second. i.e. if you use 1 Joule of energy per second, your power consumption is 1 Watt. Energy intake = 8,374,000 Joules (calc. earlier) Time = 1 day convert to seconds Do I remember how many seconds in a day? Certainly not!

43 Average power usage Time: 1 day 24 hours/day 60 minutes/hour 60 seconds / minute = 86,400 seconds

44 Average power usage Power = Energy / Time SI Units: 1 Watt = 1 Joule / Second Energy = 8,374,000 Joules (calc. earlier) Time = 1 day = 86,400 seconds Avg. Power = 8,374,000 J / 86,400 s = J / s = 96.9 Watts Avg. Power W = 100 W. (estimate!)

45 Average power usage We just calculated that your body s average power input (from food) is 100 W. This is the same as your average power output. (Assuming steady weight): Your body consumes as much energy as it expends you re not accumulating energy until you start to glow, or losing it until you disappear!

46 Jumping exercise Recall that when jumping / doing knee bends, I said we were expending ~100 W. You were actually expending ~ W, i.e. more than your average power But as I said, 100 W is an order of magnitude value, designed to give a sense of the scale involved.

47 Review By what factor is your average total power usage (as a 21st century US citizen) greater than the average power output of a human body? A. 1 they are the same B. 10 C. 100 D Avg. total power usage = 10 kw = 100 x 100 W

48 Important concepts So far... Unit conversion! SI units for power (W), energy (J) 1 Watt = 1 Joule / second From earlier... Powerand energy are not the same thing! Power = Energy / Time These are often confused by the public