Today

3. Today Making and distributing electrical energy. 39.0% of US consumption (Table 1.3) Text section 3.4-3.5 All power point images are only for the exclusive use of Phys3070/Envs3070 Spring term 2014

4. 2000 kWh/year228 watts

7. Electrical energy The most versatile, useful, simple form of energy, easily sent around. Power(Watts)= Voltage (V=Volts) Current (I=Amperes) = I*V Heat power from electricity= I2 R, with R=resistance in ohms, I in Amperes to give heat power in Watts. Three new metric names---Volts, Amperes and Ohms Wires have resistance, so send electrical power at least I, highest V

8. Transformers • Transformers Power in = power out, but change V and I. IinVin = Iout Vout Step up to send at high voltage, low current, step down to lower voltages, higher current as you get nearer the house. • Only works with Alternating Current = AC • Circuit breakers = fuses Stop the current if something is wrong, since high current makes high heat.

10. eplant=62/500=12.4% elight = 2 / 500=0.4%

11. How do we combine several generators? • Each makes alternating current, and the phase must agree if they are on the same grid. • The US electrical grid is vast and complex, operating best under steady conditions. • Loads are predictable • How to incorporate fluctuating sources, such as wind and sunshine?

13. The hard part of a grid Arrange the rotation of each generator such that the voltage from each arrives at your house ‘in phase’. Otherwise, one generator is just pushing current into another generator. The US uses 60 Hz= 60 swings of voltage per second.

16. Tres Amigas A Direct Current connection

17. The grid is more reliable than a single generating plant, But—when the grid fails, the disaster is larger.

19. a power billRJP Excel October 2012 Summer rate 241.38 kWh * $0.04604/kWh=$11.11 Nonsummer 38.62 kWh*$0.04604=$1.78 Wind surcharge 280 kWh*$0.021588=$6.04 Transmission 280 kWh*$0.000040 = $0.01 Taxes etc $42.05 $0.04604/kWh$0.174 per kWh

22. The Smart Grid • Turn the refrigerator power on only when prices are cheap, moment-by-moment. If it warms up too much, use even expensive electricity. • Charge your electric car only at night.

24. 1.The Fischer-Tropsch process turns coal (carbon=C) into gasoline=octane (=C8H18) by a series of chemical reactions. The first reaction combines carbon with water (steam) and heat to make water gas or coal gas, a mixture of hydrogen and carbon monoxide. C+H2OH2 + CO. More hydrogen is added to run the F-T reaction. The final reaction is 17 H2 + 8 CO C8H18 + 8 H2O. A)(5) How many molecules of carbon do you need to react to make enough CO to make one molecule of octane? One carbon molecule makes one CO molecule, 8 CO’s make one octane, or 8 carbon molecules make one molecule of octane. (there will also be carbon burned to provide the heat to make these reactions happen.) B) (5) How many tons of carbon do you need to react to make one ton of CO? Each carbon molecule has a relative mass of 12, each molecule of CO has a mass of 12+16=28. One ton of CO needs 12/28 tons of carbon = 0.43 tons. (You also need to burn coal to create the heat to drive the reaction.)

25. 1C)(10) How many tons of octane can you make from that one ton of CO (and the other ingredients)? The total relative weight of CO is 8*(12+16)=224, and the weight of the one octane molecule is 8*12 + 18*1 = 114. Or said another way, you make 114 tons of octane from 224 tons of CO, which means you need 114/224 tons of CO to make one ton of octane, =0.509 tons of CO. (The reason this is so low is that the oxygen in CO is heavier than the H in octane.) BONUS—how many tons of carbon are needed for that ton of octane? 8 carbons have a relative mass of 8*12=96. Each octane molecule has a mass of 8*12 + 18*1 = 114, as above. You need 96/114 tons of carbon = 0.842 tons to make one ton of octane, or you get 1/0.842 = 1.19 tons of octane from one ton of carbon. The difference is that you added hydrogen to carbon to make octane.

26. 2. (10) There is a temperature difference between very deep ocean water (4 deg C) and surface waters (25 deg C). This difference allows you to construct a heat engine. What is the best possible (Carnot) efficiency for such a hypothetical engine? Why don’t remote tropical islands use this for power? Tcold=4 deg C=4+273 = 277 deg K Thot = 25 deg C = 25+273 = 298 deg K eCarnot = 1 – Tcold/Thot = 1 – 277/298 = 1-0.9295 = 0.0705 = 7.05% This is a VERY inefficient heat engine, and any machinery to make electricity would be very complex.

27. 3.(5) Instead, image a heat engine that burns waste on that island and exhausts its waste heat into that 25 deg C water. How hot must the fire be (in deg C) to attain 30% Carnot efficiency? Now Tcold=25 deg C = 298 deg K. e=0.30=1 – Tcold/Thot = 1-298/Thot Thot=298 / (1-e) = 298 / 0.70 =426 deg K = 153 deg C

28. 5.a) (5) If Congress taxes CO2 at $40 per ton (of CO2), what is the tax on one ton (2000 pounds) of burned coal which is 60% carbon? One ton of coal holds 0.60 tons of carbon. Each ton of carbon burned makes 44/12 tons of CO2, so 0.60 tons of burned carbon makes 0.60 * 44/12 = 2.2 tons of CO2, taxed at $40/ton * 2.2 tons = $88. b)(5) How much heat energy can you get from burning that coal? Take the book value per ton of coal to represent this 60% variety. Front cover, that coal yields 2.81 *1010 J= 7800 kWhr = 2.66*107 Btu (your choice of units, all are OK)

29. c)(5) What is the tax on one ton of burned methane (CH4)? First, write the reaction for complete combustion in air. CH4 +2O2  CO2 + 2H2O, with relative masses : (12+4) + (4*16) (12+32) + 2*(2+16), or 16+ 6444+36, which balances. 16 tons of burned methane make 44 tons of CO2, so one ton of methane makes 44/16=2.75 tons of CO2 Tax = $40/ton * 44/16 tons = $110. (the difference arises because oxygen is heavier than hydrogen in the molecules) d) (5) Methane gas has a density of 0.0443 pounds per cubic foot. How many cubic feet are in that ton? 1 ton = 2000 pounds. Volume = 2000 pounds / 0.0443 pounds/cubic foot = 45,147 cubic feet = 45.147 thousand cubic feet (which is the text way of giving gas energy content)

30. e) (5) How much heat energy can be gained from that ton of methane? Use the book number for natural gas. 45.147 thousand cubic feet *[1.09*109 J=303 kWhr =1.035*106 Btu] per thousand cubic feet =[49.21*109 J = 13,680 kWhr = 46.73*106 Btu]. Your choice of units again. All are OK. Each is larger by a factor of 1.76 than for the coal.

31. f)(10) Make a brief summary of what you would write Rep. Polis (D-2d District of CO) about these four energy and tax numbers. Burning one ton of methane is taxed more than one ton of burned coal, by a factor of $110/$88=1.25. The government gains more taxes by making the industry burn gas, but industry burns that gas to get heat energy, so the relative amounts of energy from gas and coal must also come into the discussion. The ratio of heat gained from burning coal and from burning gas to the amount of harmful CO2 is computed from Heat gained/tons of CO2 = 2.66*107 Btu / 2.2 tons = 1.21*107 Btu per ton for coal And = 4.673*107 Btu/2.75 tons = 1.699*107 Btu per ton for gas. You get more energy per ton of CO2 from gas than from coal, per unit by a factor of 1.669/1.22 = =1.4. This ratio holds in any of the sets of units, so long as you are consistent.

32. Friday Energy for transportation 27.3% of US energy usage (Table 1.3) Chapter 8, especially Table 8.2 The many changes since the text will be emphasized.