1. Where will our energy come from? Ch. 16 All from the Sun

2. A problem: Dependence on imported oil Cost to the economy: 350 billion dollars per year (2011 prices) Transferred to foreign (hostile) oil producers, unpredictable interruptions 25 20 15 10 5 0 195019601970198019902000 Million barrels per day US consumption US production

3. Finding more oil Producing oil gets more costly, riskier, dirtier (deep sea, fracking, tar sands). Deep Sea Middle East North Africa Middle East, North Africa Tar sands Enhanced Oil Recovery

4. Oil recovery from tar sands in Alberta Requires large amounts of hot water, leaves tar-contaminated water.

5. Horizontal wells are drilled into gas-filled rock formations ( Marcellus shale ). Explosives create paper-thin cracks in the rock, which release trapped gas. Water, sand, and chemicals are pumped into the well (4000 gallons/minute). The sand keeps the cracks open after the water pressure is released. New source of gas and oil, cleaner than coal, abundant reserves. Consumes lots of water, contaminates it with chemicals, risk of contaminating the water supply with methane where the well punches through am aquifer. Natl. Geographic, Breaking Fuel From the Rock, December 2012, p. 90Breaking Fuel From the Rock Well meets water supply Natural gas from fracking

6. Oil from fracking Drilling for oil in North Dakota Each well contains a vertical and a horizontal part (dot and line, about 2 miles deep/long) Currently about 8,000 wells in North Dakota. They produce more oil than Alaska. Planned increase to about 40,000 wells. One well uses 2 million gal- lons of water plus 350 barrels of chemicals over its lifetime. Most of the contaminated water is pumped back deep into the ground. Natl. Geographic, March 2013, p.47

7. Supply and demand are far apart Wind Demand Solar Renewable Energy

8. Electricity from wind power

9. Electricity from photovoltaics Growing rapidly, but still a small fraction of the consumption ( 400 GW in the US ). Annual Solar Cell Production (from PVNews) Data from PVNews 4/2009, 5/2010, 5/2011

10. 100  100 km 2 of solar cells could produce all the electricity for the US. 0.4 TW US Electricity Consumption Photovoltaics: Electricity from the Sun Take it from the source. Electricity is fully convertible (Lect. 7, Slide 4). TW = TeraWatt = 1000 GigaWatt

11. The required area of solar cells All the rooftops in the US could generate 0.66 TW (NREL study 44073.pdf, p.5). Incorporation into buildings eliminates the need for costly support structures. 1 kW/m 2 (Incident solar power)  ¼(Useful daylight)  0.16(Efficiency of a solar cell)  10 10 m 2 (100  100 km 2 ) = 0.4 TW = Electric power consumed in the US

12. Polycrystalline silicon solar cell Most common, but requires a lot of energy to make.

13. Solar cell array at Nellis Air Force Base, Nevada

14. Thin film solar cells Compound semiconductors ( Cadmium Telluride, CIGS, … ) Less material, less energy (low temperature processing) Print solar cells like newspaper (roll-to-roll) Nanosolar (San Jose)

15. Many designs, efficiency growing slowly …

16. … but efficiency demands a price Physics Today, March 2007, p. 37 1 $ /W Goal High end Low end Low end designs are more cost-effective (less $ /W).

17. How much would it cost to generate all the electricity in the US by solar cells ? 1 $ /W (Price of solar cells per Watt)  0.4 TW (Electric power generated in the US) = 0.4 T $ = 0.4 Trillion Dollars The mechanical support structure adds significant costs. But one can design buildings to provide the support.

18. Price comparison between solar and fossil energy Solar energy is free, while fossil fuels need to be paid for. One-time cost for solar, continuous costs for fossil energy. Energy payback time matters for solar energy (1-4 years).Energy payback time The price of solar cells is only about 1⁄3 of the total cost. The rest is for the support structure, the converter, labor. $ /W $ /Ws

19. Solar thermal power plant in Spain Convert solar energy to steam, then to electricity the conventional way. The mirrors focus sunlight onto a steam generator at the top of the tower.

20. How do we use energy ? 1. Electricity 2. Fuel 3. Heat 1.Electricity is easy to use, but difficult to store. 2.Fuel is easy to store, but creates pollution. 3.Heat is easy to produce, but difficult to transport.

21. How does nature convert solar energy to chemical energy ? Convert plants into fuel: Make ethanol, diesel fuel from sugar, corn starch, plant oil, cellulose... Split water into hydrogen and oxygen using sunlight. Use hydrogen as fuel. No greenhouse gases. Still at the research stage. Fuel from the Sun Photosynthesis Biofuels Water splitting (artificial photosynthesis)

22. Photosynthesis Plants convert solar energy into chemical energy (here glucose, a sugar): 6 CO 2 + 6 H 2 O + photons  C 6 H 12 O 6 + 6 O 2 About 2% of the solar energy gets converted. Next slide

23. Light-harvesting proteins Next slide

24. The photosynthetic center 4 manganese atoms and 1 calcium form the reaction center.

25. Biofuels Production of ethanol fuel from corn and sugar cane: Need energy for fertilizer, farm machinery, distilling. (National Geographic, Oct. 2007, p. 44-47) Output/Input = 1.3 Output/Input = 8 Poor return, competes with food Much better return

26. Cellulose is abundantly available in corn stalks, wood chips, switchgrass Cellulose consists of a network of sugar molecules. If the network can be broken up into individual sugar molecules, ethanol can be produced by fermentation and distillation. Bacteria in the gut of cows and termites break up cellulose. Companies like Virent in Madison are producing such biofuel. Cellulose

27. Large amounts of land (and irrigation water) are required for replacing gasoline with biofuel. Algae can live in ocean water or sewage. Discover Magazine Nov. 2011

28. Efficiency comparison for solar energy How far could one drive a car with the solar energy provided by 100x100 m 2 (2.5 acres) of land in a year ? Biodiesel:21 500 km Bioethanol22 500 km Biomass to liquid:60 000 km Photovoltaics, electric car: 3 250 000 km (PHOTON International, April 2007, p. 106 www.photon-magazine.com)www.photon-magazine.com Solar cells are more efficient than photosynthesis (16% vs. 2%). Electric motors are more efficient than combustion engines Biomass to fuel conversion is inefficient. (90% vs. 25%).

29. Electrical Storage Chemical Storage Storing energy Energy/Weight Energy/Volume 0 10 20 30 010203040 Energy Storage Density Gasoline Batteries Supercapacitors Batteries for electric and hybrid cars, storing solar energy overnight. But batteries have 30-50 times lower energy density than fuels. Store fuel and convert it directly to electricity in a fuel cell. Ethanol

30. Fuel cell A fuel cell converts fuel directly into electricity, without creating heat by combustion. That’s why they can be 60% efficient, while the efficiency of a combustion engine is only about 25% (Lect. 7, Slide 6). In this example, hydrogen is combined with oxygen to form water plus energy. Usually, an explosion would result, but here the energy of the fuel drives elec- trons (e-) around an electrical circuit. The Apollo program used fuel cells for electric power. When the oxygen tank of Appollo13 exploded, the crew sent the famous message: “ Houston we’ve had a problem “

31. Solar hot water Best return on investment in solar energy

32. Conserve energy instead of producing more Infrared image of thermal radiation reveals leakage in the insulation. ( Red is warmer.) See also DOE/EEREDOE/EERE