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EE362L, Spring 2009 PV Arrays Solar Panels

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The incident solar radiation, in kW, on a panel surface is approximated by ... That corresponds to about 6.6kWH per 1kW rated of solar panels. ... – PowerPoint PPT presentation

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Title: EE362L, Spring 2009 PV Arrays Solar Panels


1
EE362L, Spring 2009 PV Arrays (Solar Panels)
2
Electrical Properties of a Solar Cell

Photons


n
-
type

External circuit



Junction

(e.g.
,
battery,
V


lights)



p
-
type

I

3
I-V Curve
4
  • 36 Cells in Series Make a 12V-Class Panel (Voc ?
    19V)

9 cells x 4 cells is a common configuration
  • Two 12V-Class Panels in Series Make a 24V-Class
    Array (Voc ? 38V)

5
I-V Curve
Isc
Pmax at approx. 30V
Isc
Pmax ? 0.7 Voc Isc
Voc
6
The Maximum Power Point
P0 at short circuit
P0 at open circuit
On a good solar day in Austin, you get about 1kWh
per square meter of solar panels (corresponds to
about 150W rated)
7
Earths Poles
  • Magnetic poles Created by Earths magnetic
    field
  • Can be located with a compass
  • They move along Earths surface!
  • Celestial poles Created by Earths rotation.
  • They are two
    imaginary stationary points in the sky.
  • Important for PV system applications.

Geological Survey of Canada
8
Where is the Sun?
Series of equations to get zenith and azimuth
angles see pp. 5-7 in lab doc.
9
Solar Noon
10
Sun Moves Throughout the Year
June 21
December 21
11
Sun Moves from Summer to Winter
Jun
Sep
Dec
12
Sun Moves From Winter to Summer
Jun
Mar
Dec
13
Panel Orientation is Important
Edge of PV module
Austins Latitude 30o
June 21
30o
Tropic of Cancer Latitude 23.45o
March 21 September 21
23.45o
23.45o
Equator
December 21
Tropic of Capricorn Latitude -23.45o
Earths surface
14
Panel Orientation is Important
  • Best all-year tilt Latitude
  • Best winter tilt Latitude 15
  • Best summer tilt Latitude 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
DN (Direct Normal W/m2) Tracking device points
toward sun and sees only the 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.
16
Keep Solar Radiation Monitor Lenses Clean!
17
Computing Incident Power
GH Measured sky on horizontal sensor (includes
disk of sun)
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.
(GH - DH) Est. disk of sun component on
horizontal sensor
DH Measured sky on shadowed horizontal sensor
(excludes disk of sun)
Est. disk of sun component on sensor pointed
toward sun
DN Est. total sky on sensor pointed toward sun
18
Computing Incident Power, cont.
The angle of incidence is the angle between the
suns rays and a vector normal to the panel
surface (0 means that the suns rays are
perpendicular to the panel surface)
Series of equations to get angle of incidence
see pp. 11-12 in lab doc.
19
Computing Incident Power, cont.
The incident solar radiation, in kW, on a panel
surface is approximated by
Est. disk of sun component on sensor pointed
toward sun
Measured sky on shadowed horizontal sensor
(excludes disk of sun)
About 14 is converted to electricity
Est. disk of sun component on panel surface
Multiply by surface area
Est. Watts on panel surface
20
Panels Atop ENS
Disconnected
21
Weather Forecast
http//www.nws.noaa.gov/forecasts/graphical/sector
s/southplains.phptabs
22
Panel Pairs Connected to Power Lab
Voltage at Panels
Voltage at Lab Bench
Panel Current
Use these two
23
Use a Variable Power Resistor to Sweep the Panel
I-V Curve
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

Reminder - Hand plot as you take your data points
  • Take the short circuit current and panel voltage
    reading

25
Use the Excel Solver to Curve Fit Your
Measurements
26
  • Automated way to get I-V curve
  • Suddenly connect panel to large discharged C
    (like 5 or 10 of the DBR Cs),
  • 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
Solar Radiation in Texas
28
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29
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32
Practice Problem
33
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