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Renewable Power Systems

Renewable Power Systems. Wind & PV Basics 15 October 2007 Dr Peter Mark Jansson PP PE. Aims of Today’s Lecture. Solar resources & basics PV materials & cell operation PV technology Wind resources. Solar declination.

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Renewable Power Systems

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  1. Renewable Power Systems Wind & PV Basics 15 October 2007 Dr Peter Mark Jansson PP PE

  2. Aims of Today’s Lecture • Solar resources & basics • PV materials & cell operation • PV technology • Wind resources

  3. Solar declination NOTE: Tropic of Cancer is 23.45o (N Latitude),Tropic of Capricorn is -23.45o (S Lat.)

  4. Nice link – Solar Declination • http://www.sciences.univ-nantes.fr/physique/perso/gtulloue/Sun/motion/Declination_a.html

  5. Declination responsible for day-length • North of latitude 66.55o (the Arctic circle) the earth experiences continuous light at the summer solstice • South of latitude -66.55o (the Antarctic circle) the earth experiences continuous darkness at the summer solstice • North of latitude 66.55o (the Arctic circle) the earth experiences continuous darkness at the winter solstice • South of latitude -66.55o (the Antarctic circle) the earth experiences continuous light at the winter solstice

  6. Rule of Thumb • Maximum annual solar collector performance (weather independent): • Achieved when collector is facing equator, with a tilt angle equal to latitude (north or south latitude) • Why? • In this geometry (the collector facing the equator with this tilt angle) the solar radiation it receives will be normal to its surface at the two equinoxes

  7. Solar position in sky • Sun’s location can be determined at any time in any place by determining or calculating its altitude angle (N) and its azimuth. • Azimuth is the offset degrees from a true equatorial direction (south in northern hemisphere), positive in morning (E of S) and negative after solar noon (W of S).

  8. Azimuth-s and Altitude-N

  9. Technology Aid • Sun Path Diagrams • Solar PathFinderTM • SunChart • Allows location of obstructions in the solar view and enables estimation of how much reduction in annual solar gain that such shading provides

  10. Sun Path diagram

  11. Maximize your Solar Window

  12. Magnetic declination • When determining true south with a magnetic compass it is important to know that magnetic south and true (geometric) south are not the same in North America, (or anywhere else). • In our area, magnetic south is +/- 12o west of true south

  13. Source:http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/calcDeclinationSource:http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/calcDeclination

  14. Orientation and Incoming Energy

  15. Flux changes based on module orientation • Fixed Panel facing south at 40o N latitude • 40o tilt angle: 2410 kWh/m2 • 20o tilt angle: 2352 kWh/m2 (2.4% loss) • 60o tilt angle: 2208 kWh/m2 (8.4% loss) • Fixed panel facing SE or SW (azimuth) • 40o tilt angle: 2216 kWh/m2 (8.0% loss) • 20o tilt angle: 2231 kWh/m2 (7.4% loss) • 60o tilt angle: 1997 kWh/m2 (17.1% loss)

  16. Benefits of tracking • Single axis – • 3,167 kWh/m2 • 31.4% improvement over fixed at 40o N latitude • Two axis tracking – • 3,305 kWh/m2 • 37.1% improvement over fixed at 40o N latitude

  17. Total Solar Flux • Direct Beam • Radiation that passes in a straight line through the atmosphere to the solar receiver (required by solar concentrator systems) 5.2 vs. 7.2 (72%) in Boulder CO • Diffuse • Radiation that has been scattered by molecules and aerosols in the atmosphere • Reflected • Radiation bouncing off ground or other surfaces

  18. Solar Resources - Direct Beam

  19. Solar Resources – Total & Diffuse

  20. Annual Solar Flux variation • 30 – years of data from Boulder CO • 30-year Average: 5.5 kWh/m2 /day • Minimum Year: 5.0 kWh/m2 /day • 9.1% reduction • Maximum Year: 5.8 kWh/m2 /day • 5.5% increase

  21. Benefits of Real vs. Theoretical Data • Real data incorporates realistic climatic variance • Rain, cloud cover, etc. • Theoretical models require more assumptions • In U.S. – 239 sites have collected data, 56 have long term solar measurements (NREL/NSRDB) • Globally – hundreds of sites throughout the world with everything from solar to cloud cover data from which good solar estimates can be derived (WMO/WRDC)

  22. Solar Flux Measurement devices • Pyranometer • Thermopile type (sensitive to all radiation) • Li-Cor silicon-cell (cutoff at 1100m) • Shade ring (estimates direct-beam vs. diffuse) • Pyrheliometer • Only measures direct bean radiation

  23. PV History • 1839: Edmund Becquerel, 19 year old French physicist discovers photovoltaic effect • 1876: Adams and Day first to study PV effect in solids (selenium, 1-2% efficient) • 1904: Albert Einstein published a theoretical explanation of photovoltaic effect which led to a Nobel Prize in 1923 • 1958: first commercial application of PV on Vanguard satellite in the space race with Russia

  24. Historic PV price/cost decline • 1958: ~$1,000 / Watt • 1970s: ~$100 / Watt • 1980s: ~$10 / Watt • 1990s: ~$3-6 / Watt • 2000-2007: • ~$1.8-2.5/ Watt (cost) • ~$3.50-4.75/ Watt (price)

  25. PV cost projection • $1.50  $1.00 / Watt • 2006  2008 • SOURCE: US DOE / Industry Partners

  26. PV Module Prices Source: P. Maycock, The World Photovoltaic Market 1975-1998 (Warrenton, VA: PV Energy Systems, Inc., August 1999), p. A-3.

  27. PV technology efficiencies • 1970s/1980s  2003 (best lab efficiencies) • 3  13% amorphous silicon • 6  18% Cu In Di-Selenide • 14  20% multi-crystalline Si • 15  24% single crystal Si • 16  37% multi-junction concentrators

  28. PV Module Performance • Temperature dependence • Nominal operating cell temperature (NOCT) Tc = cell temp, Ta = ambient temp (oC), S = insolation kW/m2

  29. PV Output deterioration • Voc drops 0.37%/oC • Isc increases by 0.05%/oC • Max Power drops by 0.5%/oC

  30. PV Module Shipments

  31. Wind & PV Markets (’94 -’06) Wind production PV production

  32. Wind Market

  33. PV Market

  34. Amorphous Si

  35. Amorphous Si

  36. Cadmium Telluride

  37. Multi-crystalline Si

  38. Multi-crystalline Si

  39. Single Crystal Si

  40. Semi-Conductor Physics • PV technology uses semi-conductor materials to convert photon energy to electron energy • Many PV devices employ • Silicon (doped with Boron for p-type material or Phosphorus to make an n-type material) • Gallium (31) and Arsenide (33) • Cadmium (48) and Tellurium (52)

  41. p-n junction • When junction first forms as the p and n type materials are brought together mobile electrons drift by diffusion across it and fill holes creating negative charge, and in turn leave an immobile positive charge behind. The region of interface becomes the depletion region which is characterized by a strong E-field that builds up and makes it difficult for more electrons to migrate across the p-n junction.

  42. Depletion region • Typically 1 m across • Typically 1 V • E-field strength > 10,000 V/cm • Common, conventional p-n junction diode • This region is the “engine” of the PV Cell • Source of the E-field and the electron-hole gatekeeper

  43. Band–gap energy • That energy which an electron must acquire in order to free itself from the electrostatic binding force that ties it to its own nucleus so it is free to move into the conduction band and be acted on by the PV cell’s induced E-field structure.

  44. Band Gap (eV) and cutoff Wavelength • PV MaterialsBand GapWavelength • Silicon 1.12 eV 1.11 m • Ga-As 1.42 eV 0.87 m • Cd-Te 1.5 eV 0.83 m • In-P 1.35 eV 0.92 m

  45. Photons have more than enough or not enough energy • Sources of PV cell losses (=15-24%): • Silicon based PV technology max()=49.6% • Photons with long wavelengths but not enough energy to excite electrons across band-gap (20.2% of incoming light) • Photons with shorter wavelengths and plenty (excess) of energy to excite an electron (30.2% is wasted because of excess) • Electron-hole recombination within cell (15-26%)

  46. p-n junction • As long as PV cells are exposed to photons with energies exceeding the band gap energy hole-electron pairs will be created • Probability is still high they will recombine before the “built-in” electric field of the p-n junction is able to sweep electrons in one direction and holes in the other

  47. Generic PV cell IncomingPhotons Top Electrical Contacts electrons  - - - - Accumulated Negative Charges - - - - n-type Holes E-Field Depletion Region + + + + + + + + + - - - - - - - - - Electrons p-type + + + Accumulated Positive Charges + + + Bottom Electrical Contact I 

  48. PV Module Performance • Standard Test Conditions • 1 sun – 1000 watts/m2 = 1kW/m2 • 25 oC Cell Temp • AM 1.5 (Air Mass Ratio) • I-V curves • Key Statistics: VOC, ISC, Rated Power, V and I at Max Power

  49. PV specifications (I-V curves) • I-V curves look very much like diode curve • With positive offset for a current source when in the presence of light

  50. From cells to modules • Primary unit in a PV system is the module • Nominal series and parallel strings of PV cells to create a hermetically sealed, and durable module assembly • DC (typical 12V, 24V, 48V arrangements) • AC modules are available

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