Energy and Society. Physics Society Technology and Values Professor Ani Aprahamian Guest Lecturer: Dr. Manoel Couder

Transcription

1 Energy and Society Physics Society Technology and Values Professor Ani Aprahamian Guest Lecturer: Dr. Manoel Couder

2 Renewable Energy Resources Wind Clearing up the unclear Personal investigation: Offshore vs. land: pros and cons Storage National policy to support wind power generation Chicken and egg problem: Fossil fuel to power construction of windmills (or photovoltaic cells) Damage to birds/bats Acoustic issues Answers: Re-explain the link between wind velocity and maximum energy that can be generated.

3 Assume a cubical volume of air with a mass m moving with a velocity v v Mass= Air Density * Volume L The kinetics energy of the air in the cube is: ½ *m*v 2 = ½ *r*l 3 *v 2 The cube move its own length in L/v seconds OR it takes L/v second for all the air to go through the cube right surface The rate at which this cube transports energy is the amount of kinetic energy available in the cube divided by the time it take to move it: Power=E/(L/v)=E*v/L = ½ *r*l 2 *v 3 Now we can express the wind power per unit area as: ½ *r*v 3

4 Renewable Energy Resources Wind Clearing up the unclear Personal investigation: Offshore vs. land: pros and cons Storage National policy to support wind power generation Chicken and egg problem: Fossil fuel to power construction of windmills (or photovoltaic cells) Damage to birds/bats Acoustic issues Answers: Re-explain the link between wind velocity and maximum energy that can be generated. If power generated is proportional to area covered by the blades, why not build the windmills bigger? How to maximize the efficiency of windmills? Maximum available power per unit area is known Betz law -> Maximum extractable power is ~59% Today s optimum in excess of 45% (see: energy, Environment and Climate, Richard Wolfson, W.W. Norton & Company)

5 What is the oldest form of energy exploited by humankind? FIRE What did it change? Cooking -> Nutrition improvement -> Increased amount of energy intake Protection from predator and insects Extend working hours and geographical area

6 Renewable Energy Resources Biomass Goethe: Energy will do anything that can be done in the world

7 Biomass Let s define it: According to biomass n. 1. The total mass of living matter within a given unit of environmental area. 2. Plant material, vegetation, or agricultural waste used as a fuel or energy source. Examples? Wood, plant and animals oils, grass, agricultural waste, dung, algae

8 Biomass How about petroleum is it biomass then? Is Biomass renewable? Biomass is considered a renewable energy source because the carbon in biomass is regarded as part of the natural carbon cycle: trees take in carbon dioxide from the atmosphere and convert it into biomass and when they die, it is released back into the atmosphere. Whether trees are burned or whether they decompose naturally, they release the same amount of carbon dioxide into the atmosphere. The idea is that if trees harvested as biomass are replanted as fast as the wood is burned, new trees take up the carbon produced by the combustion, the carbon cycle theoretically remains in balance, and no extra carbon is added to the atmospheric balance sheet so biomass is considered carbon neutral. Since nothing offsets the CO2 that fossil fuel burning produces, replacing fossil fuels with biomass supposedly results in reduced carbon emissions. From:

9 Biomass An indirect use of the Sun s energy Photosynthesis: 6H 2 O + 6CO x10-18 J -> C 6 H 12 O 6 + 6O 2 Globally Energy stored at a rate of 133TW Energy stored at any time 1.5x10 22 J Oxygen on earth from photosynthesis Impact on life s evolution Pictures from:

10 Biomass An indirect use of the Sun s energy Photosynthesis: 6H 2 O + 6CO x10-18 J -> C 6 H 12 O 6 + 6O 2 Efficiency of solar energy transformation: Spectral limitation (not all color are absorbed) Chemical reactions release heat Plant use 50% of the stored energy 133TW 65.5TW Upper limit :7% We need to eat, we need shelter, We already use ~40% of the planet net productivity

11 Biomass Wood electric power station Can feed the grid or just site that manufacture wood products Often combined with heat for hot water for community heating

12 Biomass Waste burning In Tibet

13 In the U.S. Biomass Waste burning In the end, what the scientists found was that burning waste is often the better option. Results of EPA s research estimate that WTE (burning) is capable of producing up to about 10 times more electricity than LFGTE (burying) from the same amount of waste. The findings for greenhouse gas emissions where particularly interesting: Even with optimum conditions for capturing methane generated from buried waste, the study showed that, per unit electricity generated, greenhouse gases emissions from landfills are two to six times higher than those generated from plants that burn waste.

14 Biomass Waste methane recovery When buried, waste can still be used

15 Biomass Fermented shredded plants release methane Next nine slides are from Wolgang Bauer, MSU

16 Slide from Wolgang Bauer, MSU

17 Slide from Wolgang Bauer, MSU

18 Slide from Wolgang Bauer, MSU

19 Slide from Wolgang Bauer, MSU

20 Slide from Wolgang Bauer, MSU

21 Slide from Wolgang Bauer, MSU

22 Slide from Wolgang Bauer, MSU

23 Slide from Wolgang Bauer, MSU

24 Slide from Wolgang Bauer, MSU

25 From Wolfgang Bauer, MSU

26 Biomass Transportation Fuel? Renewable like wind, solar and hydro can produce electricity Not so much fuels for transportation from US Department of energy YouTube channel

27 Biomass Transportation Fuel? Ethanol USA: Corn Ford Model T on ethanol/gasoline mix E10 & E15 Heavily subsidized but 2011 Senate voted to end it Energy balance? Biofuel out = 0.75 to 1.7 Fossil fuel in New effort to move away from corn

28 Biomass Transportation Fuel? Ethanol USA: Corn Ford Model T on ethanol/gasoline mix E10 & E15 Heavily subsidized but 2011 Senate voted to end it Energy balance? Biofuel out = 0.75 to 1.7 Fossil fuel in New effort to move away from corn This graph shows how much fossil energy is required to provide 1 BTU of each fuel at the pump. The graph does not reflect energy derived from solar or other renewable sources used in the production of ethanol.

29 Biomass Transportation Fuel? (Source: F.O. Licht 'World Fuel ethanol Production' chart from World Ethanol and Biofuels report Vol 7, No.9/ , page 175)

30 Biomass Transportation Fuel? Biodiesel (Source: Eurostat (historical data)

31 Biomass Transportation Fuel? Biodiesel (Source: F.O. Licht's 'Global Biodiesel Production capacity' chart from World Ethanol and Biofuels report Vol 7, No.9/ , page 176)

32 Biomass Environmental impact? Societal impact? Use of fossil fuel in farming equipment - how much energy in? Does burning a ~30 years old tree really renewable? Need to be optimized to location: Brazil s sugarcane is more efficient Cogeneration: Usage of heat generated in burning or fermentation process for water heating How about competition with food production?

33 Renewable Energy Resources Article to read from a special section of SCIENCE magazine August 13, 2010 Vol. 329, p Articles: Scaling up Alternative Energy (9) 1. Do We have the energy for the next energy transition? 2. Solar Energy- Sending African Sunlight to Europe 3. What about cellulose based ethanol? 4. Energy s Tricky trade-offs 5. Wind power- where do you site them? 6. Feedstocks for biofuels. 7. Challenges in Scaling up Biofuels 8. An Outlook on Micro-algal Biofuels 9. Two-stage nuclear renaissance