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Solar Energy: The Ultimate Renewable Resource Xiangfeng Duan.

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Presentation on theme: "Solar Energy: The Ultimate Renewable Resource Xiangfeng Duan."— Presentation transcript:

1 Solar Energy: The Ultimate Renewable Resource Xiangfeng Duan

2 What is Solar Energy? Originates with the thermonuclear fusion reactions occurring in the sun. Originates with the thermonuclear fusion reactions occurring in the sun. Represents the entire electromagnetic radiation (visible light, infrared, ultraviolet, x-rays, and radio waves). Represents the entire electromagnetic radiation (visible light, infrared, ultraviolet, x-rays, and radio waves). Radiant energy from the sun has powered life on Earth for many millions of years. Radiant energy from the sun has powered life on Earth for many millions of years.

3 Advantages and Disadvantages Advantages Advantages All chemical and radioactive polluting byproducts of the thermonuclear reactions remain behind on the sun, while only pure radiant energy reaches the Earth. All chemical and radioactive polluting byproducts of the thermonuclear reactions remain behind on the sun, while only pure radiant energy reaches the Earth. Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused! Energy reaching the earth is incredible. By one calculation, 30 days of sunshine striking the Earth have the energy equivalent of the total of all the planet’s fossil fuels, both used and unused! Disadvantages Disadvantages Sun does not shine consistently. Sun does not shine consistently. Solar energy is a diffuse source. To harness it, we must concentrate it into an amount and form that we can use, such as heat and electricity. Solar energy is a diffuse source. To harness it, we must concentrate it into an amount and form that we can use, such as heat and electricity. Addressed by approaching the problem through: Addressed by approaching the problem through: 1) collection, 2) conversion, 3) storage. 1) collection, 2) conversion, 3) storage.

4 Solar Energy to Heat Living Spaces Proper design of a building is for it to act as a solar collector and storage unit. This is achieved through three elements: insulation, collection, and storage. Proper design of a building is for it to act as a solar collector and storage unit. This is achieved through three elements: insulation, collection, and storage.

5 Solar Energy to Heat Water A flat-plate collector is used to absorb the sun’s energy to heat the water. A flat-plate collector is used to absorb the sun’s energy to heat the water. The water circulates throughout the closed system due to convection currents. The water circulates throughout the closed system due to convection currents. Tanks of hot water are used as storage. Tanks of hot water are used as storage.

6 Photovoltaics Photo+voltaic = convert light to electricity Photo+voltaic = convert light to electricity

7 Solar Cells Background French physicist A. E. Becquerel first recognized the photovoltaic effect French physicist A. E. Becquerel first recognized the photovoltaic effect first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold to form the junctions first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold to form the junctions Bell Laboratories, experimenting with semiconductors, accidentally found that silicon doped with certain impurities was very sensitive to light. Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical device for converting sunlight into useful electrical power. Resulted in the production of the first practical solar cells with a sunlight energy conversion efficiency of around 6% Bell Laboratories, experimenting with semiconductors, accidentally found that silicon doped with certain impurities was very sensitive to light. Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical device for converting sunlight into useful electrical power. Resulted in the production of the first practical solar cells with a sunlight energy conversion efficiency of around 6% First spacecraft to use solar panels was US satellite Vanguard First spacecraft to use solar panels was US satellite Vanguard 1

8 Driven by Space Applications in Early Days

9 The heart of a photovoltaic system is a solid-state device called a solar cell. How does it work

10 Energy Band Formation in Solid  Each isolated atom has discrete energy level, with two electrons of opposite spin occupying a state.  When atoms are brought into close contact, these energy levels split.  If there are a large number of atoms, the discrete energy levels form a “continuous” band.

11 Energy Band Diagram of a Conductor, Semiconductor, and Insulator a conductora semiconductor an insulator  Semiconductor is interest because their conductivity can be readily modulated (by impurity doping or electrical potential), offering a pathway to control electronic circuits.

12 Silicon  Silicon is group IV element – with 4 electrons in their valence shell.  When silicon atoms are brought together, each atom forms covalent bond with 4 silicon atoms in a tetrahedron geometry.

13 Intrinsic Semiconductor  At 0 ºK, each electron is in its lowest energy state so each covalent bond position is filled. If a small electric field is applied to the material, no electrons will move because they are bound to their individual atoms. => At 0 ºK, silicon is an insulator.  As temperature increases, the valence electrons gain thermal energy. If a valence electron gains enough energy (Eg), it may break its covalent bond and move away from its original position. This electron is free to move within the crystal.  Conductor Eg <0.1eV, many electrons can be thermally excited at room temperature.  Semiconductor Eg ~1eV, a few electrons can be excited (e.g. 1/billion)  Insulator, Eg >3-5eV, essentially no electron can be thermally excited at room temperature.

14 Extrinsic Semiconductor, n-type Doping Electron - Si As Extra Valence band, E v E g = 1.1 eV Conducting band, E c E d ~ 0.05 eV  Doping silicon lattice with group V elements can creates extra electrons in the conduction band — negative charge carriers (n-type), As- donor.  Doping concentration #/cm 3 (10 16 /cm 3 ~ 1/million).

15 Valence band, E v E g = 1.1 eV Conducting band, E c E a ~ 0.05 eV Electron - Si B Hole  Doping silicon with group III elements can creates empty holes in the conduction band — positive charge carriers (p-type), B-(acceptor). Extrinsic Semiconductor, p-type doping

16 V I R O F p n p n V>0V<0 Reverse bias Forward bias p-n Junction (p-n diode)  A p-n junction is a junction formed by combining p-type and n-type semiconductors together in very close contact.  In p-n junction, the current is only allowed to flow along one direction from p-type to n-type materials. i p n V<0 V>0 depletion layer - +

17  Solar Cells  Light-emitting Diodes  Diode Lasers  Photodetectors  Transistors p-n Junction (p-n diode)  A p-n junction is the basic device component for many functional electronic devices listed above.

18 How Solar Cells Work  Photons in sunlight hit the solar panel and are absorbed by semiconducting materials to create electron hole pairs.  Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. p n - + hv > E g

19 The Impact of Band Gap on Efficiency Efficiency,  = (V oc I sc FF)/P in V oc  E g, I sc  # of absorbed photons Efficiency,  = (V oc I sc FF)/P in V oc  E g, I sc  # of absorbed photons Decrease E g, absorb more of the spectrum Decrease E g, absorb more of the spectrum But not without sacrificing output voltage But not without sacrificing output voltage hv > E g Current Density (mA/cm 2 ) Voltage (volts) J sc V oc FF Dark Light J mp V mp Fill Factor, FF = (V mp I mp )/V oc I sc Efficiency,  = (V oc I sc FF)/P in

20 Cost vs. Efficiency Tradeoff Efficiency   1/2 Long d High  High Cost d Long d Low  Lower Cost d  decreases as grain size (and cost) decreases Large Grain Single Crystals Small Grain and/or Polycrystalline Solids

21 Cost/Efficiency of Photovoltaic Technology Costs are modules per peak W; $0.35-$1.5/kW-hr

22 89.6% of 2007 Production 45.2% Single Crystal Si 42.2% Multi-crystal SI 42.2% Multi-crystal SI Limit efficiency 31% Limit efficiency 31% Single crystal silicon % efficiency Single crystal silicon % efficiency Multi-crystal silicon % efficiency Multi-crystal silicon % efficiency Best efficiency by SunPower Inc 22% Best efficiency by SunPower Inc 22% Silicon Cell Average Efficiency First Generation – Single Junction Silicon Cells

23 CdTe 4.7% & CIGS 0.5% of 2007 Production New materials and processes to improve efficiency and reduce cost. New materials and processes to improve efficiency and reduce cost. Thin film cells use about 1% of the expensive semiconductors compared to First Generation cells. Thin film cells use about 1% of the expensive semiconductors compared to First Generation cells. CdTe – 8 – 11% efficiency (18% demonstrated) CdTe – 8 – 11% efficiency (18% demonstrated) CIGS – 7-11% efficiency (20% demonstrated) CIGS – 7-11% efficiency (20% demonstrated) Second Generation – Thin Film Cells

24 Enhance poor electrical performance while maintaining very low production costs. Enhance poor electrical performance while maintaining very low production costs. Current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques. Current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques. Multi-junction cells – 30% efficiency (40-43% demonstrated) Multi-junction cells – 30% efficiency (40-43% demonstrated) Third Generation – Multi-junction Cells

25 Solar Home Systems Space Water Pumping Telecom Main Application Areas – Off-grid

26 Residential Home Systems (2-8 kW) PV Power Plants ( > 100 kW) Commercial Building Systems (50 kW) Main Application Areas Grid Connected

27 Future Energy Mix

28 Renewable Energy Consumption in the US Energy Supply, 2007

29 Top 10 PV Cell Producers Top 10 produce 53% of world total Q-Cells, SolarWorld - Germany Sharp, Kyocera, Sharp, Sanyo – Japan Suntech, Yingli, JA Solar – China Motech - Taiwan

30 (in the U.S. in 2002) 1-4 ¢ ¢ 6-8 ¢ 5-7 ¢ Production Cost of Electricity 6-7 ¢ ¢ Cost, ¢/kW-hr

31 Future Generation – Printable Cells Organic Cell Nanostructured Cell Solution Processible Semiconductor

32 Organic Photovoltaics Convert Sunlight into Electrical Power. Trans-polyacetylene (t-PA)Polythiophene (PT)Polypyrrole (PPY)

33 Nanotechnology Solar Cell Design

34 Interpenetrating Nanostructured Networks

35 Dye Sensitized Solar Cell


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