Physics Professor Ani Aprahamian. Science Literacy. Chapter 3: Energy

Transcription

1 Physics Professor Ani Aprahamian Science Literacy Chapter 3: Energy

2 What can we do about it? Renewable Energy Resources? Solar Wind Hydropower Waves Geothermal

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4 If we have such inexhaustible solar energy ~6000 Times more than all of humanity s energy needs. What is the problem? 1. Not all of the Electromagnetic Spectrum is absorbed 2. Solar cells have to be sensitive to visible part of EM spectrum 3. Efficiency of solar cells 4. Storage of Energy 5. Not there when it is cloudy less there in the winter 6. Not there at night Solar cells: Improve efficiency and cost!!!!!!!!!!!!!! Now 10-15% of solar energy is converted into electrical energy Research cells up to 30% efficiency..not yet deployed in market

5 Energy Security.Natural Gas?? h"p://youtu.be/73mv- Wl5cgg

6 What can we do about it? Renewable Energy Resources? Solar Wind Hydropower Waves Geothermal

7 The U.S. & Its Energy Future Fossil Fuels Oil, coal, natural gas Renewable Energy Sources Solar energy, wind Active and Passive Solar Base Load vs. Peak Load

8 Photovoltaics is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.

9 Photovoltaic modules and arrays produce direct-current (dc) electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.

10 Solar Photovoltaic Panels Can Be Used in Various Ways

11 Solar Thermal Facility in Barstow, California

12 Example. The roof area of an average home is 150 m 2 and that of a car is about 7m 2. The average US household energy consumption is 3.5 kw. a. How does this compare with the mid-day solar power incident on a typical house roof? b. How about a 300 horsepower car? c. Is it practical to have totally powered solar cars and homes? Sun shines at 1 kw/m2 what determines this??? House: 1kW/m2 x 150m2= 150 kw Car: 1 horsepower = 0.75 kw so 300 horsepower = 300 x 0.75 kw=225 kw Sun shining with 1 kw/m2 x 7 m2 =7 kw

13 Electricity Generated from Wind Turbines

14 80-Meter Wind Resource Maps

15 Can t store the energy.

16 Power that can be extracted from the wind is proportional to the cube of he wind s velocity and the area swept out by the blades. Why Cube? Velocity of wind v Motion of blades.1/2 mv 2 Kinetic Energy = ½ mv 2 Mass= mass of air that hits the wind-generator blades in a unit of time Power output is also related to the area swept out by the blades; Area= diameter 2 Maximum achievable efficiency by wind turbines 59% Maximum power output= 2.83 x 10-4 d 2 v 3 kwatts ; 2.36x10-6 d 2 v 3 D is in meters; v=m/s ; d is in feet; v= miles/hr

17 What is the maximum achievable power output of a wind turbine of blade radius 2m in a 25 mph wind? 2.36x10-6 d 2 v 3 Diameter = 2 x radius = 4m convert to feet.. 4m x 3.28 ft/m= ft Power = (13.08ft) 2 (2.36x10-6 ) (25 mph) 3 = 6.3 kwatts

18 Transportation Electric vehicles Battery Short range Hybrid vehicles Gas and battery Many new models Fuel Cell vehicles Hydrogen Uses fossil fuel to create hydrogen

19 Hybrid Car Chevy Volt

20 Transportation Facts: 100% dependent on petroleum ~60% of petroleum is imported ~30% of US greenhouse gas emissions

21 What can we do about Transportation? Energy Efficiency with respect to transportation Near term improve efficiencies of cars/trains/etc. improve engines/diesel/hybrids/transmissions/weight of automobiles Medium term changes in power-train and vehicle technologies hybrid-electric full battery-electric vehicles Longer term new technologies hydrogen fuel cells? Hydrogen distribution infrastructure

22 Where does this oil go? SubsKtuKon is difficult Passenger vehicles consume about 80% of our imports.

23 Energy Use by type of vehicle

24 What are the issues? Efficiency Conservation New Technologies

25 Most Energy Efficient Transportation Mode? Did you know that the bicycle is the most energy efficient transportation mode? It is 3 times more efficient than walking, 5 times more efficient than using the train and 15 to 20 times more efficient than driving a car.

26 Physics: Power = Energy /time Energy = force x distance Force for moving a car..

27 . Forces for moving a car Total Force Forces due to accelerating + Forces of going upward (hills) + Forces for resisting rolling + Forces associated with aerodynamic drag = Total Force

28 . Forces for moving a car Total Force first piece: Forces due to acceleration F=ma =mass of the car x acceleration =mass of the car x(change in velocity) Driving: 0-60 miles per hour in 10 seconds.. 1 mile = 5280 feet Initial velocity =0 mph Final velocity = 60 mph Change in velocity = 60 mph/10 seconds 60 miles/hr x 5280ft/mi x 1hr/3600s=88 ft/s Per 10 s.. Acceleration = 8.8 ft/s 2

29 Forces for moving a car Total Force Forces due to accelerating (F=ma) + Forces of going upward (hills) =mgh = m x g x incline or steepness (slope) = mgs

30 Forces for moving a car Total Force Forces due to accelerating (F=ma) + Forces of going upward (hills) (F=mgs) + Forces from resistance F= C r mv C r is specific to a car of course so is the mass

31 Forces for moving a car Total Force Forces due to accelerating (F=ma) + Forces of going upward (hills) (F=mgs) + Forces from resistance (F= C r mv) + Forces from aerodynamic drag

32 Forces for moving a car Total Force Forces due to accelerating (F=ma) + Forces of going upward (hills) (F=mgs) + Forces from resistance (F= C r mv) + Forces from aerodynamic drag F is proportional to C D A f v 2 C D is aerodynamic drag coefficient A f is the frontal Area of the car v is velocity it goes as velocity squared

33 Physics: Power = Energy /time = Force x distance /time = Force x velocity Energy = force x distance Force for moving a car..

34 Energy losses in a car In gasoline-powered vehicles, over 62 percent of the fuel's energy is lost in the internal combustion engine (ICE). ICE engines are very inefficient at converting the fuel's chemical energy to mechanical energy, losing energy to engine friction, pumping air into and out of the engine, and wasted heat.

35 What speed should you drive to get the best mileage??? In general, smaller, lighter, more aerodynamic cars will get their best mileage at higher speeds. Bigger, heavier, less aerodynamic vehicles will get their best mileage at lower speeds.

36 Motor Fuel Tax Rates for Selected Countries Cents/gallon COUNTRY GASOLINE DIESEL Belgium France Germany Italy Japan Netherlands United Kingdom United States 39 45

37 U.S. mileage standards for cars up for first <me Fri Mar 27, :40pm EDT WASHINGTON (Reuters) - The U.S. government on Friday imposed the first increase in mileage standards for passenger cars and boosted the floor for sport uklikes and pickups beginning with model year 2011 vehicles. "These standards are important steps in the nakon's quest to achieve energy independence," said TransportaKon Secretary Ray LaHood, who added that work on future mileage programs must take into account the health of U.S.

38 The standard, which is expected to cost industry $1.4 billion in vehicle design and other changes, would require compacts, sedans and other passenger cars to average 30.2 miles per gallon in combined city/ highway driving, up from the 27.5 mpg standard that was established in the late 1970s under the Corporate Average Fuel Economy (CAFE) program.

39 How green are electric cars? Internal combustion engine 15% efficient Electricity has to be produced somehow Efficiency of plants to produce electricity from petroleum 38% Efficiency of electric cars 40% 0.40 x 0.38 = 0.15 about the same.as ICE

40 Storage of energy/power in an electric car? Batteries.slow to charge lose power while charging can t store very much energy

41 Example Each person in the USA consumes an energy equivalent of 58 barrels of oil/year. How many tons of coal is that? 1 barrel of oil=5.8 x10 6 Btu 58 barrels= 58 x 5.8 x10 6 Btu=3.36x10 8 Btu 1 ton of coal (2000lbs) = 2.66x10 7 Btu 3.36x10 8 Btu /2.66x10 7 Btu/ton= 12.6 tons or lbs of coal kg How many grams of Uranium is that? 1 gram of Uranium= 7.84x10 7 Btu 3.36x10 8 Btu/7.84x10 7 Btu/g of U = 4.3 g

42 Example A bicyclist on a flat road expends energy at the rate of 100 watts. How many calories of energy are expended in five minutes of peddling? 100 watts = 100 J/s 5 minutes x 60 s/min = 300 seconds 100 J/s x 300 s= 30,000 J 1 calorie= J 30,000 J/ (4.184 J/cal)= 7170 calories or 7.2 Calories