renewable energy course#04
TRANSCRIPT
Solar Power
Solstices
June solstice - North Pole is tilted 23.5o towards the Sun relative to the circle of illumination. All places above a latitude of 66.5oN are in 24 hours of sunlight, while locations below a latitude of 66.5oS are in darkness.
Equinoxes
Equinoxes – Earth’s axis is not tilted toward or away from the Sun and the circle of illumination cuts through the poles. Red circles are the Arctic Circle.
Equinoxes, Solstices, Aphelion, and Perihelion
Relationship of maximum Sun height to latitude for the equinox (left) and June solstice (right). The red values on the right of the globes are maximum solar altitudes at solar noon. During the equinox, the equator is the location on the Earth with a Sun angle of 90 degrees for solar noon
Solar Altitude
α = Sin-1[Sin δ Sin φ + Cos δ Cos ω Cos φ]
φ is latitude
Hour Angle
ω = 15 (ts – 12) (degrees)
ts is local solar time in hours
Declination Angleδ = Sin-1 [0.39795 Cos [0.98563 (N-173)]]
Hour Angle
Declination Angle (between the equatorial
plane and the sun-earth line)
Variation of Declination Angle
Solar Altitude Angle
Observer
Zenith Angle
Solar Spectrum and Solar Constant
1367 W/m2
Seasonal Variation of Extraterrestrial Radiation
Total Daily Extraterrestrial Solar Radiation on a Horizontal Surface
Ho,h = 86,400 Io [ωs Sin Φ Sin δ + Cos δ Cos Φ Sin ωs] / π (J/m2)
Io = Isc [1 + 0.34 cos {2πN / 365.25}] is the solar constant
Isc = 1367 Watt
ωs = cos–1[- tan(δ) tan(Φ)] is the hour angle of sunset in radians
-Ve before noon & +Ve after noon
Instantaneous Extraterrestrial Solar Radiation on a Horizontal Surface
Ioh = Io [cos δ cos Φ cos ω + sin δ sin Φ]
Photocell Response
Heliostat, Albuquerque
Designing & Fabrication of a 2-kW Parabolic Trough Solar Thermal Power Plant
Storage Requirement
Extraterrestrial Radiation on a Surface Normal to Sun
Annual cosine effect reduces solar radiation on a horizontal surface by 39% - equator, 52% - 40o latitude, 74% - 80o latitude.
Ground Level Radiation Attenuation Effect
Effect of Air Mass on Spectral Irradiance on the Ground
Air Mass = 1 for sea level normal Irradiance
Sun rise & Sun set > 30 air mass
Air mass
AM = 1/[cos θz + 0.50572 (96.07995 – θz) -1.6364]
θz = Zenith angle = 90o at sunset
Solar Radiation Attenuation Due to Air Mass
I = 1.1 x Ioh x 0.7(AM)**(0.678)
factor of 1.1 accommodates the 10% diffused radiation
Attenuation of Normal Solar Radiation Versus Azimuth Angle
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100
Azimuth Angle (degrees)
Air
Mas
s / S
ola
r R
adia
tio
n
Air Mass
Solar Radiation (25 W units)
Solar Radiation Measurement
Pyranometer
Normal Incidence Pyrheliometer
Global Solar Irradiance on a mostly Sunny day and a mostly Cloudy day
750 MW Imperial Valley Project of 250 kW Solar Dish Striling Engines
Linear Freznel