EE535: Renewable Energy: Systems, Technology & Economics. Session 4: Solar (1): Solar Radiation. Annual solar radiation on a horizontal surface at the equator is over 2000kWh/m 2 In Northern Europe this falls to about 1000kWh/m 2 (per annum)
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Session 4: Solar (1): Solar Radiation
Annual solar radiation on a horizontal surface at the equator is over 2000kWh/m2
In Northern Europe this falls to about 1000kWh/m2 (per annum)
The tilt between the sun and the land reduces the intensity of the midday sunSolar Radiation
Energy from the sun in the form of ultra-violet, visible and infra-red electromagnetic
radiation is known as solar radiation
Ultraviolet 0.20 - 0.39µ
Visible 0.39 - 0.78µ
Near-Infrared 0.78 - 4.00µ
Infrared 4.00 - 100.00µ
Flux of solar radiation incident on a surface placed at the top of the atmosphere, depends on time t, geographical location (latitude φ, longitude λ, and on the orientation of the surfaceOrientation
E(t, Ф, λ) = S(t)cos Ф(t , Ф, λ)
S(t) is known as the solar constant
δ is the declination of the sun
ώ is the hour angle of the sun
Ф is the angle between the incident
solar flux and the normal to the surface
The solar constant is the amount of incoming solar electromagnetic radiation
per unit area that would be incident on a plane perpendicular to the rays,
at a distance of one astronomical unit (AU) (roughly the mean distance from
the Sun to the Earth).
The sun produces light with a distribution similar to what would be expected from a 5525 K (5250 °C) blackbody, which is approximately the sun's surface temperature
Radiation interacts with matter in several ways:
ReflectionSolar radiation spectrum for direct light at both the top of the Earth’s atmosphere and at sea level
[Insolation is a measure of solar radiation energy received on a given surface area in a given time.
It is commonly expressed as average irradiance in watts per square meter (W/m2) per day.
In the case of photovoltaics it is commonly measured as kWh/(kWp·y) (kilowatt hours per year per kilowatt peak rating). ]
The European Commission's Joint Research Centre, Institute for Environment and Sustainability
n – day of year (days since Jan 1st )
h = hour angle
L = Latitude
The optimal solar device tilt
Can be estimated from:
The declination angle, denoted by d, varies seasonally due to the tilt of the Earth on its axis of rotation and the rotation of the Earth around
the sun. If the Earth were not tilted on its axis of rotation, the declination would always be 0°.
However, the Earth is tilted by 23.45° and the declination angle varies plus or minus this amount.
Only at the spring and autumn equinoxes is the declination angle equal to 0°.
S Daniels relations