1. Topics of discussion
1. Terminology about the motion of the sun
2. Irradiance over the course of a day and
year
3. Irradiance directly from the sun vs from
the blue sky
4. Spectral irradiance
5. Energy and Power
6. Map of Oregon
7. Power production using solar panels
2. SRML Mission Statement
• At the University of Oregon Solar Resource
Monitoring Lab (SRML) we measure the
irradiance of sunlight.
– At all times of day
– At all times of year
– Under all weather conditions
– All over the Pacific Northwest
• Irradiance is a measure of the power per area in
light
– Units: W/m2
3. Motion of sun across sky
SouthEast West
Directly
above
you
http://scienceblogs.com/startswithabang/files/2009/12/winter_solstice_pivato.jpg
4. How to describe the sun’s location
North
East
South
West
Zenith
(up)
AZM
ELV
SZA
Azimuthal Angle (AZM): Angle measured clockwise from North
Elevation Angle (ELV): Angle measured up from the horizon
Solar Zenith Angle (SZA): Angle measured down from vertical
ELV + SZA = 90°
5. Motion of sun across sky
SouthEast West
Solar Noon
SZA ≈ 70 °
AZM = 180°
Time = 12:00
Winter
Sunset
SZA = 90 °
AZM ≈ 240°
Time ≈ 04:30
Solar Noon
SZA ≈ 20 °
AZM = 180°
Time = 12:00
Winter
Sunrise
SZA = 90 °
AZM ≈ 120°
Time ≈ 07:30
Summer
Sunrise
SZA = 90 °
AZM ≈ 60°
Time ≈ 05:00
Summer
Sunset
SZA = 90 °
AZM ≈ 300°
Time ≈ 20:00
6. The
vertical
axis is the
height of
the sun
above the
horizon.
6:00
7:00
8:00
9:00
10:0
0
11:0
0
12:0
0
13:0
0
14:0
0
15:0
0
16:0
0
17:0
0
18:0
0
19:0
0
East South West
Azimuthal Angle (AZM)
ElevationAngle(ELV)
The blue curves show
the location of the
sun on specific days
The red curves show
the location of the
sun at specific hours.
The horizontal axis is the east/west location of the sun
http://solardat.uoregon.edu/SunChartProgram.html
Horizon
ELV = 0 °
SZA = 90°
Directly
overhead
ELV = 90 °
SZA = 0°
7. How the path length of light through
the atmosphere affects the irradiance
• In the summer light travels through less atmosphere.
Smaller path length → Less light absorbed → More irradiance → Summer
• In the winter light travels through more atmosphere.
Longer path length → More light absorbed → Less irradiance → Winter
Winter
sun
Summer
sun
NOTE: Not drawn to scale
The atmosphere is significantly thinner
(and the sun is much bigger and farther away)
Imagine two different
times of the year in
Eugene Oregon at noon.
Summer vs Winter
As light travels through
the atmosphere some
of the light is absorbed.
8.
9.
10.
11.
12.
13. Yearly fluctuations in irradiance due to
seasonal changes.
GHI at 12 PM, 2000 – 2005, Eugene, OR
14. Diffuse Radiation (DHI)
Light coming from:
• Clouds
• Air molecules in the sky
• Ground reflection (buildings,
trees, ground)
Direct Radiation (DNI)
• Light directly from sun
Solar radiation
monitoring sensor
This detector is observing light
coming directly from the sun and
also from other parts of the sky
This is called global irradiance (GHI)
15. Measuring light from different sources
GHI = Global horizontal
irradiance
DHI = Diffuse horizontal
irradiance
DirHI = Direct horizontal
irradiance
DNI = Direct normal
irradiance
• Light only coming from
the sun
• Measured on a surface
perpendicular to the light
• Light coming from
all parts of the sky
• Measured on a
horizontal surface
• Light not coming
directly from the sun
• Measured on a
horizontal surface
• Light only coming
from the sun
• Measured on a
horizontal surface
16. Shade Ball
Casts shadow
DHI sensor
In shadow of shade ball
Observes the sky
Does not observe sun
GHI sensor
Observes sky and sun
DNI
Observes the sun
Does not observe sky
Monitoring Station in Eugene Oregon
(Roof of Pacific Hall)
26. Power
• Irradiance is a measure of
power per area
• Power is the rate at which
energy is delivered
• P =
𝑑𝐸
𝑑𝑡
• We measure this.
Energy
• Users often want to know
how much energy is
available in a day
• Add up all the energy
throughout the day
• E = 𝑃 𝑑𝑡
• We compute this from
the irradiance data
• The area under the
irradiance vs time graph
29. The solar resource in different
locations
• The SRML has
solar
monitoring
stations
throughout
the Pacific
Northwest
30. Go to the map and…
• Go to the map and find four locations.
1. Smallest solar resource in the summer
2. Smallest solar resource in the winter
3. Largest solar resource in the summer
4. Largest solar resource in the winter.
• It will probably be useful for you to make a
take a few notes
39. Solar lab kits
• The SRML has developed a solar lab kit.
• The kits are designed to get students to
explore the basic properties of solar cells.
40. Solar lab kit teaching options
• The simple yet versatile solar lab kits allow
students to explore science in many different
ways.
• Voltage and current in series and parallel
• Electrical power (P = I V)
• The properties of solar cell
• The dot product of two vectors
• How to compute the efficiency of a system
• An understanding of how solar could be
implemented into the power grid.
41. Compute the area needed to power
the American lifestyle
• Measure the power of a single solar cell
– Measure the voltage across a known resistor
– P = V2/R
• Measure the area of the single solar cell
• Compute the area needed to generate all their power
– The typical American uses around 10 kW of power
– This would require around 600 m2 (after reductions in
efficiency are accounted for)
• Compute the area needed to power the state of
Oregon
– ~1.18% of the state would need to be covered in solar
panels
42. Thank you for attending
• Contact information
– Josh Peterson
– jpeters4@uoregon.edu
– 541-346-4745
• SRML website
– solardat.uoregon.edu
43.
44. Lesson Plan
• How are the GHI, DHI, and DNI related?
– Come up with an equation that consistently relates the three terms.
• HINTS:
• Global horizontal irradiance is a measure of how much light is reaching a horizontal surface. This light is coming from
the sun and the blue sky.
• Direct normal irradiance is a measure of how much light is reaching a surface facing the sun. This light is only coming
directly from the sun. (There is no light coming from the blue sky.)
• Diffuse Horizontal Irradiance is a measure of how much light is reaching a horizontal surface. This light is only coming
from the blue sky. (There is light no light coming directly from the sun).
• The location of the sun is important.
• For the set of data given on the following page, determine an equation that relates the GHI, DNI, and DHI. You should be
able to use the equation at all times of the day.
Answer: GHI = DNI * Cos(SZA) + DHI
Note that the SZA is given in degrees, make sure your
calculator is reading degrees and not radians.
46. Follow up questions
• Approximately what time does the sun rise?
• Is the sun ever directly overhead (straight up)?
47. Take away lessons
• A sample data set to use statistics on
• Mean, Median,
• Standard deviation
• Use of the dot product
– DirHI = DNI * Cos (SZA)
• Extraterestrial vs ground (look at spectrum, why
is sky blue)
48. • Intro traditional lecture
– Intro to our work
– Motion of sun
– Energy vs power
• Location 1
– Watch sun move (passage of a day)
– clouds
• Location 2
– Year
• Location 3
– GHI DHI DNI
• Location 4
– How much power is this for one standard rooftop (10 m x 10 m) ?
• Bike/person, lightbulb, toaster, vacuum, pinwheel moving, 1 kg at a height of 1 meter
– How much energy is this for 1 day one day on a standard roof top (10 m x 10 m)
• 1 gallon of gasoline, 1 jelly doughnut, 2000 Calories, 1 hour running
• Location 4
– Spectrum
• Location 5
– Solar kits
• Location 6
– Move around map
• Move up into atmosphere
• Intro traditional lecture
– Intro to our work
– Motion of sun
• Location 1
– Start in space earth move
– Come down to earth
– Watch sun move (passage
– clouds
• Location 2
– Year
• Location 3
– GHI DHI DNI
• Location 4
– Spectrum
• Location 5
– Solar kits
• Location 6
– Move around map
• Move up into atmosphere
49. Purpose of talk
• A bit about how the sun moves across the sky
• Information about irradiance
• Different types of light (GHI, DNI, DHI)
• Terminology of solar terms (SZA, AZM, Hour
angle)
50. Test the solar calculator
• Go to the website:
– https://www.nrel.gov/midc/solpos/solpos.html
• Enter the correct information about your time and location
– In Oregon the time zone is -8
– Keep the pressure and temperature as the default values. (they are only correction terms)
• Ignore the optional input values:
• Check desired output values:
– Solar azimuthal angle (the angle from north
• North = 0, East = 90, South = 180, West = 270, etc.
– Solar Zenith angle, degrees from zenith, refracted
• This is the angle to the sun from straight up
• Equipment:
– Meter sticks (or other long rod of known length)
– Compass
– Tape measure
– A sunny day
– A nice place to sit outside
• Go to a flat horizontal surface (example a football field.
– Make sure that the compass is working properly. If there is Iron in the vicinity compasses sometimes don’t actually tell you north.
– The magnetic field of the earth is not actually at the north pole.
– In Eugene the magnetic field points 15° East of North. So the actual north pole is 15 degrees to the left of the north pole the compass gives you.
– https://www.ngdc.noaa.gov/geomag-web/#declination
• Place the meter stick vertical
– Mark the location of the base of the meter stick.
– The end of the meter stick in the air should produce a shadow on the ground. Mark the location of the end of the shadow
– Measure the angle from north to the location of the meter stick
• Add 180° to it to get the azimuthal angle of the sun (test it against the solar calculator)
• Computing the azimuthal angle.
– In the diagram below mark the lengths of the sides of the triangle.
– HINT: you know the lengths of two of the sides.
Teachers Note:
You may find it easier to have the students mark a large sheet of
paper with a line designated as North.
Then have the students rotate the paper until the north on the
paper is actually aligned with the north pole. In Oregon the
Once the paper is aligned correctly don’t move it.
NOTE: The magnetic north pole of the compass is not at the
same location as the geographic north pole (the axis of the
earth).
I am not sure which north pole Santa clause lives at.
NOTE2: The actual magnetic north pole is located in antartica
and the magnetic south pole is located
51. 1st Class Stations:
• One minute data collection
• Measuring DNI, GHI and DHI
• Measure atmospheric conditions
• Calibrated yearly
• Eugene OR, 1975 – Present
• Burns OR, 1979 – Present
• Hermiston OR, 1980 – Present
• Dillon MT, 2002 – Present
• Twin Falls ID, 2002 – Present
• Seattle WA, 2015 – Present
Subsidiary Stations:
• One to fifteen minute data collection
• Measuring DNI, GHI and DHI
.
53. Clouds in the morning.
• No direct sunlight (DNI = 0)
• All light is diffuse (GHI = DHI)
Clear sky in the afternoon.
GHI = DNI * Cos(SZA) + DHI
2015 Aug, 15
Eugene, OR
Irradiance vs Time of day
IrradianceW/m2
GHI
DNI
DHI
55. Energy involved in various activities
• 1 MJ = 1,000,000 Joules
• 1 mile run = 0.46 MJ
• 1 apple = 0.65 MJ
• 1 movie at home (on the TV) = 1.4 MJ
• 2000 Calorie diet = 8.4 MJ
• 1 hot shower = 23.2 MJ
• 1 gallon of gasoline = 127MJ
• 1 kWH = 3.6 MJ
Small energy
Large energy
56. Energy vs Power
• Irradiance is a measure
of power per area
• It is useful to know the
total energy delivered
• P =
𝑑𝐸
𝑑𝑡
• E = 𝑃 𝑑𝑡
• The energy delivered a
day is add
Distance vs Speed
• Speed is the rate at
which the position
changing in time
• v =
𝑑𝑥
𝑑𝑡
• x = v 𝑑𝑡
