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Where will our energy come from ?

Where will our energy come from ?. Comparison of power plants for 1 GW. Hydroelectric: 60,000 tons of water per second. Coal: 10,000 tons of coal per day (1 freight train). Nuclear: 100 tons of uranium per year. Where is solar energy ?.

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Where will our energy come from ?

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  1. Where will our energy come from?

  2. Comparison of power plants for 1 GW Hydroelectric: 60,000 tons of water per second Coal: 10,000 tons of coal per day (1freight train) Nuclear: 100 tons of uranium per year

  3. Where is solar energy? Although most of our energy originally comes from the Sun (except nuclear), only a minuscule amount of solar energy is being used today.

  4. A problem: Dependence on imported oil 25 • Cost to the economy: $700 B/yr (peak prices), $200 B/yr (average prices) • Transferred to foreign (hostile) oil producers, unpredictable interruptions US consumption 20 15 Million barrels per day 10 5 US production 0 1950 1960 1970 1980 1990 2000 Find alternative energy sources: Solar, wind, biofuel, …

  5. Wind Demand Supply and demand are far apart Solar

  6. Storing energy • Chemical energy is easy to store in fuel, but electricity is not. • How do we store solar electricity overnight, wind electricity when calm? • The range of all-electric cars is short due to poor storage by batteries. 30 Energy Storage Density Gasoline Energy/Volume Ethanol 20 10 Batteries 0 Supercapacitors 0 10 20 30 40 Chemical Storage Electrical Storage Energy/Weight • Batteries have30-50 times lower energy density than gasoline.

  7. How do we use energy? • Electricity • Fuel • Heat • Electricity is easy to use, but difficult to store. • Fuel is easy to store, but creates pollution. • Heat is easy to produce, but difficult to transport.

  8. 0.4 TW US Electricity Consumption Electricityfrom the Sun (photovoltaics) 100100 square kilometers of solar cells could produce all the electricity for the US. But they are still too costly.

  9. 1 kW/m2 (Incident solar power)  1/4 (Fraction of useful daylight)  0.16 (Efficiency of a solar cell 16%)  100100 ·106 m2 (100100 km2) = 4·108 kW (Electric power generation in the US) The required area of solar cells

  10. Solar cell power plants Growing rapidly almost everywhere, but the total production was less than 1 GW in 2003 (about one nuclear power plant).

  11. Solar cells

  12. Polycrystalline silicon solar cell

  13. Thin film solar cells • Compound semiconductors: CdTe, CIGS = Cu(InGa)Se • Less material, less energy by low temperature processing • Print solar cells like newspaper (roll-to-roll) Solar cell printed on plastic Nanosolar (San Jose, Berlin)

  14. The efficiency keeps growing slowly

  15. PV Module Production Experience (or “Learning”) Curve 1976 “80% Learning Curve”:Module price decreases by20% for every doubling ofcumulative production Silicon Wafer Technologies 2010 2015 2005 80% • Slow power law, not exponential like Moore’s law • Slope of the double-log plot gives the power (1/3)

  16. Goal 1 $/W High end Low end But efficiency demands a price Physics Today, March 2007, p. 37

  17. 1 $/W (Price of solar cells)  4·108 kW (Electric power generated in the US) = 4·1011 $ = 400 Billion Dollars How much would it cost to generate all the electricity in the US by solar cells? The support structure adds substantial costs.

  18. Solar thermalConvert solar energy to steam, then to electricity

  19. Solar thermal (31% efficiency)

  20. Fuel from the Sun? • Photosynthesis • Biofuels • Split Water Plants convert solar energy to chemical energy but the efficiency is low (1%-2%) Convert plants to 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. (Futuristic)

  21. 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

  22. Cellulose 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. We are still searching for an efficient way to do the same.

  23. Biofuels versus photovoltaics (PV) How far could one drive a car with the energy produced by 100x100 m2 (2.5 acres)of land in a year? Biodiesel: 21500 km Bioethanol 22500 km Biomass to liquid: 60000 km Photovoltaics,electric car: 3250000 km Solar cells are more efficient than photosynthesis. Electric motors are more efficient than combustion engines. PHOTON International, April 2007, p.106 (www.photon-magazine.com)

  24. Solar water heater Currently the best return on investment in solar energy

  25. Conserve energy rather than produce more An infrared image of thermal radiation reveals weak spots in the insulation.

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