Download - Solar Radiation - Solar Panel · PDF file2012 Jim Dunlop Solar Solar Radiation: 2 - 2 Overview Defining basic terminology associated with solar radiation, including solar irradiance

2012 Jim Dunlop Solar
Chapter 2
Solar Radiation
Terminology & Definitions Geometric & Atmospheric Effects Solar Power & Energy
Measurements & Data
PresenterPresentation NotesSolar energy is the fuel that creates and sustains life on earth. The nature and characteristics of the solar radiation resource are of fundamental importance in understanding how solar PV systems are designed and perform.
References: Photovoltaic Systems, Chap. 2National Renewable Energy Laboratory - Renewable Resource Data Center: www.nrel.gov/rredc

2012 Jim Dunlop Solar Solar Radiation: 2 - 2
Overview
Defining basic terminology associated with solar radiation, including solar irradiance (power), solar irradiation (energy) and peak sun hours.
Identifying the instruments used for measuring solar radiation.
Understanding the effects of the earths movements and atmospheric conditions on the solar energy received on the earths surface.
Locating the suns position using sun path diagrams and defining the solar window.
Accessing solar radiation data resources and quantifying the effects of
collector orientation on the amount of solar energy received.
PresenterPresentation NotesReference: Photovoltaic Systems, p. 25

Sun - Earth Relationships
Sun: Diameter: 865,000 miles (1,392,000 km, 109 times earth) Mass: 2 x 1030 kg (330,000 times earth) Density: 1.41 g/cm3 Gravity: 274 m/s2 (28 g) Surface Temperature: 10,000 F (5800 K)
Earth: Diameter: 7,930 miles (12,756 km) Mass: 5.97 x 1024 kg Density: 5.52 kg/cm3 Gravity: 9.81 m/s2 (1 g) Typical Surface Temperature: 68 F (300K) Earths Orbit Around Sun: 1 year Earths Rotation about its Polar Axis: 1 day
93 million miles, average (1.5 x 108 km)
1 Astronomical Unit (Distance traveled in 8.31 minutes at the Speed of Light)
PresenterPresentation NotesA comparison of the physical properties for the sun and earth illustrate the vast differences.
Reference: Photovoltaic Systems, p. 26-27

Solar Radiation
Solar radiation is electromagnetic radiation ranging from about 0.25 to 4.5 m in wavelength, including the near ultraviolet (UV), visible light, and near infrared (IR) radiation.
Common units of measure for electromagnetic radiation wavelengths: 1 Angstrom () = 10-10 meter (m) 1 nanometer (nm) = 10-9 meter 1 micrometer (m) = 10-6 meter 1 millimeter (mm) = 10-3 meter 1 kilometer (km) = 1000 meters
NASA
PresenterPresentation NotesThe sun produces immense quantities of electromagnetic radiation. The tiny fraction reaching the earths surface amounts to approximately 170 million gigawatts (GW), many thousands of times greater that the electrical power used on earth. Note that the United States has just over 1000 GW of electrical power generation.

Electromagnetic Spectrum
Wavelength (m)
near infra-red
near ultra-violet
Visible light
0.3 0.5 0.7
Wavelength
Gam
ma
rays
1
10
100
0.1 m
1 m
m
1 m
10
m
100 m
10 m
m
100
mm
1 m
10 m
100
m
103 m
104 m
105 m
X ra
ys
Ultr
avio
let R
adia
tion
Visi
ble
Ligh
t
Infr
ared
Rad
iatio
n
Mic
row
aves
Shor
t Rad
io
Wav
es (F
M/T
V)
AM
Rad
io
Long
Rad
io W
aves
Solar spectrum
0.25 m 4.5 m
PresenterPresentation NotesThe electromagnetic spectrum ranges from short wavelength gamma rays and x-rays, to long wavelength radio waves. The solar spectrum includes visible light and near infrared radiation.
Reference: Photovoltaic Systems, p. 30

Solar Irradiance (Solar Power)
Solar irradiance is the suns radiant power, represented in units of W/m2 or kW/m2.
The Solar Constant is the average value of solar irradiance outside the earths atmosphere, about 1366 W/m2.
Typical peak value is 1000 W/m2 on a terrestrial surface facing the sun on a clear day around solar noon at sea level, and used as a rating condition for PV modules and arrays.
1 m
1 m One
Square Meter
Typical peak value per m2
1000 watts = 1 kilowatt
PresenterPresentation NotesSolar irradiance is suns radiant power incident on a surface of unit area, commonly expressed in units of kW/m2 or W/m2. The Solar Constant is the value of solar irradiance outside the earths atmosphere on a surface facing the suns rays, which averages about 1366 W/m2. Due to atmospheric effects, typical peak values of terrestrial solar irradiance are on the order of 1000 W/m2 on surfaces at sea level facing the suns rays under clear sky conditions around solar noon. Consequently, 1000 W/m2 is used as a solar irradiance reference condition for rating the peak output for PV modules and arrays.

Solar Irradiance
Time of Day
Sola
r Irr
adia
nce
(W/m
2 )
Sunrise Noon Sunset
For south-facing fixed surfaces, solar power varies over the day, peaking at solar noon.
PresenterPresentation NotesFor south-facing fixed (non-tracking) surfaces on a clear day, the incident solar irradiance varies over the day in a bell-shaped curve, peaking at solar noon.

Solar Irradiation (Solar Energy)
Solar irradiation is the suns radiant energy incident on a surface of unit area, expressed in units of kWh/m2. Typically expressed on an average daily basis for a given month. Also referred to as solar insolation or peak sun hours.
Solar irradiation (energy) is equal to the average solar irradiance (power) multiplied by time.
Peak sun hours (PSH) is the average daily amount of solar energy received on a surface. PSH are equivalent to: The number of hours that the solar irradiance would be at a peak level of
1 kW/m2. Also the equivalent number of hours per day that a PV array will operate
at peak rated output levels at rated temperature.
PresenterPresentation NotesSolar irradiation is the suns radiant energy incident on a surface of unit area, commonly expressed in units of kWh/m2/day for monthly averages and a given surface orientation. Insolation is also a term used to represent solar irradiation. Solar energy data are used to estimate the performance of buildings and solar energy utilization systems.

Solar Power and Solar Energy
Time of Day
Sola
r Irr
adia
nce
(W/m
2 )
Sunrise Noon Sunset
Solar irradiation (energy) is the area under the solar irradiance (power) curve
Solar irradiance (power)
PresenterPresentation NotesSimilar to electrical power and energy, solar power and solar energy are related by time. The amount of solar energy received on a surface over a given period of time is equal to the average solar power over the period multiplied by the time. Graphically, solar irradiation (energy) is the area under the solar irradiance (power) curve.

Peak Sun Hours
Time of Day (hrs)
Sola
r Irr
adia
nce
(W/m
2 )
1000 W/m2
Sunrise Noon Sunset
Peak Sun Hours
Solar Insolation
Solar Irradiance Area of box equals
area under curve
PresenterPresentation NotesPeak sun hours (PSH) represents the average daily amount of solar energy received on a surface, and equivalent to the number of hours that the solar irradiance would be at a peak level of 1 kW/m2 to receive the same amount of energy. It is also the equivalent number of hours per day that a PV array will operate at its peak rated output levels at rated temperature.
Peak Sun Hours = # equivalent hours @ 1 kW/m2 irradiance.
Worldwide, the solar energy resource averages around 5 PSH (5 kWh/m2/day) on optimally oriented fixed surfaces facing the sun.

Solar Power and Energy: Examples
The solar power incident on a surface averages 400 W/m2 for 12 hours. How much solar energy is received? 400 W/m2 x 12 hours = 4800 Wh/m2 = 4.8 kWh/m2 = 4.8 PSH
The amount of solar energy collected on a surface over 8 hours is
4 kWh/m2. What is the average solar power received over this period? 4 kWh/m2 / 8 hours = 0.5 kW/m2 = 500 W/m2
A PV system produces 6 kW AC output at peak sun and average
operating temperatures. How much energy is produced from this system per day if the solar energy received on the array averages 4.5 peak sun hours? 6 kW x 4.5 hours/day = 27 kWh/day
PresenterPresentation NotesAverage solar power multiplied by time in hours equals solar energy. Solar power defines the instantaneous output of a PV system, while the amount of solar energy accumulated defines the amount of energy produced and the equivalent n

Download - Solar Radiation - Solar Panel · PDF file2012 Jim Dunlop Solar Solar Radiation: 2 - 2 Overview Defining basic terminology associated with solar radiation, including solar irradiance

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