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4 ee462_l_solar_ppt

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4 ee462_l_solar_ppt

  1. 1. 1 EE462L, Spring 2014 PV Arrays (Solar Panels)
  2. 2. 2 Electrical Properties of a Solar Cell n-type p-type – V + I Photons Junction External circuit (e.g., battery, lights) Isc – V + I )1( −BV eA External circuit (e.g., battery, lights) )1( −BV eA 0 5 0.0 0.6Diode Volts DiodeAmps Diode current )1( −BV eA )1( −−= BV sc eAII
  3. 3. 3 I-V Curve V I Isc Voc Im Vm , where A, B, and especially Isc vary with solar insolation 0 0 Increasing solar insolation Maximum power point
  4. 4. 4 • 36 Cells in Series Make a 12V-Class Panel (Voc ≈ 19V) • Two 12V-Class Panels in Series Make a 24V-Class Array (Voc ≈ 38V) 9 cells x 4 cells is a common configuration
  5. 5. 5 ( )100524.034.5)( 1777.0 −−= V eVI I-V Curve Isc Voc Isc Pmax at approx. 30V Pmax ≈ 0.7 • Voc • Isc
  6. 6. 6 The Maximum Power Point P=0 at short circuit P=0 at open circuit Pmax On a good solar day in Austin, you get about 1kWh per square meter of solar panels (corresponds to about 150W rated)
  7. 7. 7 Earth’s Poles • Magnetic poles: Created by Earth’s magnetic field Can be located with a compass They move along Earth’s surface! • Celestial poles: Created by Earth’s rotation. They are two imaginary stationary points in the sky. Important for PV system applications. Geological Survey of Canada
  8. 8. 8 Where is the Sun? Figure 4. Sun Zenith and Azimuth Angles West North (x axis) Line perpendicular to horizontal plane East (y axis) Horizontal plane Up (−z axis) Note – because of magnetic declination, a compass in Austin points approximately 6º east of north. Series of equations to get zenith and azimuth angles – see pp. 5-7 in lab doc.
  9. 9. 9 Solar Noon
  10. 10. 10 Sun Moves Throughout the Year June 21 December 21
  11. 11. 11 Sun Moves from Summer to Winter Jun Dec Sep
  12. 12. 12 Sun Moves From Winter to Summer Dec Jun Mar
  13. 13. 13 Panel Orientation is Important June 21 December 21 March 21 September 21 Equator Tropic of Cancer Latitude 23.45o Tropic of Capricorn Latitude -23.45o Austin’s Latitude: 30o 23.45o 23.45o 30o Edge of PV module Earth’s surface
  14. 14. 14 Panel Orientation is Important Line perpendicular to horizontal plane Horizontal plane Figure 6. Panel Tilt Angle Line perpendicular to panel surface Edge of panel • Best all-year tilt = Latitude • Best winter tilt = Latitude + 15° • Best summer tilt = Latitude – 15°
  15. 15. 15 Solar Radiation Monitors Rotating Shadowband Pyranometers Measure GH and DH NREL Sci Tec Two-Axis Tracker Measures DN, GH, and DH GH (Global Horizontal W/m2 ): Sensor points straight up, sees entire sky, including sun disk DH (Diffuse Horizontal W/m2 ): Once per minute, band quickly swings over, shadow falls on sensor. Then, sensor sees entire sky, less sun disk. DN (Direct Normal W/m2 ): Tracking device points toward sun and sees only the sun disk
  16. 16. 16 Keep Solar Radiation Monitor Lenses Clean!
  17. 17. 17 Computing Incident Power )cos( )( zenith sun est DHGH DHDN θ − += Direct normal (DN), global horizontal (GH), and diffuse horizontal (DH), all in W/m2 , are the three important components of solar radiation. DN can be estimated from GH and DH. DH: Measured sky on shadowed horizontal sensor (excludes disk of sun) GH: Measured sky on horizontal sensor (includes disk of sun) (GH − DH): Est. disk of sun component on horizontal sensor Est. disk of sun component on sensor pointed toward sun DN: Est. total sky on sensor pointed toward sun
  18. 18. 18 Computing Incident Power, cont. incidentβ The angle of incidence is the angle between the sun’s rays and a vector normal to the panel surface (0° means that the sun’s rays are perpendicular to the panel surface) Series of equations to get angle of incidence – see pp. 11-12 in lab doc.
  19. 19. 19 Computing Incident Power, cont. panelincidentzenith sun incident A DHGH DHP •         • − += )cos( )cos( )( β θ The incident solar radiation, in kW, on a panel surface is approximated by About 14% is converted to electricity Est. disk of sun component on sensor pointed toward sun Measured sky on shadowed horizontal sensor (excludes disk of sun) Est. disk of sun component on panel surface Multiply by surface area Est. Watts on panel surface
  20. 20. 20 Panels Atop ENS All panels atop ENS have azimuth angle = 190o View Facing Front of ENS Panels (i.e., looking toward north) (Note – areas shown are for individual panels, so for a pair, double the values shown) Station 18 BP Station 19 BP Station 18 BP Station 17 BP Station 16 Solarex Station 16 Solarex Station 19 BP Station 17 BP Station 15 Solarex Station 15 Solarex Station 21 Photowatt Station 21 Photowatt Area of each panel is 0.54m2 Area of each panel is 0.52m2 Area of each panel is 0.60m2 Station 20 BP Area of this panel is 1.04m2 80W each 150W 85W each 85W each Disconnected
  21. 21. 21 Weather Forecast http://www.nws.noaa.gov/forecasts/graphical/sectors/southplains.php#tabs
  22. 22. 22 Panel Pairs Connected to Power Lab Voltage at Panels Voltage at Lab Bench Panel Current Use these two
  23. 23. 23 Use a Variable Power Resistor to Sweep the Panel I-V Curve
  24. 24. 24 Record, Plot, and Visually Inspect the I-V Data Points as You Take Them •Take the open circuit voltage reading with no load connected •Adjust the power resistor, backing down in integer volts in two volt steps (e.g. 38V, 36V, 34V, … ) until about 25V, while taking the current readings •At about 25V, continue to back down in integer volts, but in five volt steps, while taking the current readings •Take the short circuit current and panel voltage reading Reminder - Hand plot as you take your data points
  25. 25. 25 PV Station Isc= 5.340E+00 I = Isc − A(exp(BVpanel) − 1) A= 5.241E-03 B= 1.777E-01 di/dv R(v) Vpanel Vload I I equation (I error)^2 Ppanel = VI P equation equation equation 39 0 -1.818E-02 0.00033 0.0 -0.7 -9.31E-04 1073.6 35 2.65 2.710E+00 0.003654 92.8 94.9 -9.31E-04 1073.6 30 4.3 4.262E+00 0.00148 129.0 127.8 -9.31E-04 1073.6 25 4.95 4.899E+00 0.002558 123.8 122.5 -9.31E-04 1073.6 20 5.15 5.162E+00 0.000138 103.0 103.2 -9.31E-04 1073.6 4 5.3 5.334E+00 0.001178 21.2 21.3 -9.31E-04 1073.6 0.009338 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 PV Station, Bright Sun 0 1 2 3 4 5 6 0 5 10 15 20 25 30 35 40 45 V(panel) - volts I-amps Use the Excel Solver to Curve Fit Your Measurements
  26. 26. 26 0 5 10 15 20 25 30 35 40 0 0.5 1 1.5 2 Seconds Voltage Current I - V 0 1 2 3 4 5 6 0 10 20 30 40 Power 0 20 40 60 80 100 120 140 0 0.5 1 1.5 2 Seconds Automated way to get I-V curve: • Suddenly connect panel to large discharged C (like 5 or 10 of the DBR C’s), • Capture I and V data points on a scope, save to a floppy, and read the file with Excel, • Replot I versus V, • Replot P versus time to get max P
  27. 27. 27 Solar Radiation in Texas AVERAGE DIRECT NORMAL INSOLATION MAP LEGEND per YEARCOLOR KEY per day (kWh/m2 -day) (MJ/m2) (quads/100 mi2 ) <3.0 <3,940 <1.0 3.0 - 3.5 3,940 - 4,600 1.0 - 1.1 3.5 - 4.0 4,600 - 5,260 1.1 - 1.3 4.0 - 4.5 5,260 - 5,910 1.3 - 1.5 4.5 - 5.0 5,910 - 6,570 1.5 - 1.6 5.0 - 5.5 6,570 - 7,230 1.6 - 1.8 5.5 - 6.0 7,230 - 7,880 1.8 - 1.9 6.0 - 6.5 7,880 - 8,540 1.9 - 2.1 6.5 - 7.0 8,540 - 9,200 2.1 - 2.3 >7.0 >9,200 >2.3
  28. 28. 28
  29. 29. 29 Multiply by panel efficiency, e.g. 0.14, to get electrical output
  30. 30. 30 clock noon solar noon
  31. 31. 31 Solar analysis of Sept. 25, 2006. Assume panels are at 30º tilt, 180º azimuth. Incident kWH on 1m2 panel (approx. 150W rated) is 7.02kWH. Multiplying by 0.14 efficiency yields 0.98 kWH. That corresponds to about 6.6kWH per 1kW rated of solar panels (1000*0.98/150). Thus, if a (non-air conditioned) house consumes 20 kWH per day, then about 3kW of panels are needed. Using $2.5 per W, which inflates to about $7.0 per W with mounting and electronics, then the 3 kW of panels cost about $21K. Consider an average price of electricity for residential users of 11 cents/kWH (TX is about average). So cost of electricity each day is about $2.1. Hence, it will take close to 3 years to pay the solar
  32. 32. 32 In recent years, financial incentives have acted like catalysts to increase PV power penetration and to bring solar panels costs down
  33. 33. 33 • Other factors affecting PV use effectiveness and return of investment: - Air conditioner impact - PV panel orientation (SW is better during the summer because it tends to maximize generation when air conditioner consumption is maximum)
  34. 34. 34 December 16 was a brilliant solar day here in Austin. Consider a PV installation that has 60º tilt, and 225º azimuth (i.e., facing southwest). Use the following equation, , and the graphs on the following page to estimate 5a. the maximum incident solar power density on the panels (in W/m2), and 5b. the time at which the maximum occurs. Practice Problem
  35. 35. 35 Zenith Incident GH DH

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