How do you calculate clearness index?
On the Solar Resource page, for each month of the year, you can enter the average radiation for the month. Based on the value of the average radiation, the month of the year, and the latitude, HOMER calculates the clearness index.
What is cloudiness index?
The clearness index is the ratio of the measured global solar radiation at the Earth’s surface to the extra-terrestrial solar radiation at the top of the atmosphere, while the cloudiness index is the ratio of the diffuse solar radiation to the global solar radiation at the Earth’s surface.
What is clear sky insolation clearness index?
9. Averaged Clear-Sky Insolation Clearness Index. SRDB name: Ins_Clearness_Index_Clr. Definition: Average amount of the total solar radiation incident on a horizontal surface at the surface of. the earth when the cloud cover is less than 10% divided by the average of incoming top-of-atmosphere.
What do you mean by atmospheric clarity index?
The clearness index is a measure of the clearness of the atmosphere. It is the fraction of the solar radiation that is transmitted through the atmosphere to strike the surface of the Earth. It is a dimensionless number between 0 and 1, defined as the surface radiation divided by the extraterrestrial radiation.
How do you calculate monthly average clearness index?
The monthly averaged clearness index K ¯ T is defined as the ratio of the monthly averaged daily total radiation on a horizontal surface to that on a corresponding surface outside the earth’s atmosphere. The ratio r d / r T is a factor that depends on solar geometry and collector tracking.
What is the role of the clearness index for estimating solar radiation for cloudy day?
The clearness index is the measured global horizontal radiation divided by the extraterrestrial radiation. It basically tells you how cloudy that moment is. If you know the clearness index, then you can calculate the extraterrestrial radiation (it does not depend on the weather) and thus calculate the solar radiation.
What is meant by solar constant S?
Solar constant, the total radiation energy received from the Sun per unit of time per unit of area on a theoretical surface perpendicular to the Sun’s rays and at Earth’s mean distance from the Sun. The value of the constant is approximately 1.366 kilowatts per square metre.
What is clear sky insolation incident on a horizontal surface?
Clear-Sky Insolation Clearness Index Amount of the total solar radiation incident on a horizontal surface at the surface of the earth with cloud cover is less than 10%; given as a fraction of insolation available at the top of the atmosphere.
What is clearness?
clearness or lucidity as to perception or understanding; freedom from indistinctness or ambiguity. the state or quality of being clear or transparent to the eye; pellucidity: the clarity of pure water.
How do you calculate diffuse solar radiation?
A fair estimate of the diffuse irradiance can be obtained by subtracting the direct normal beam radiation projected onto a horizontal surface from the global irradiance.
What is clearness index in solar?
Clearness index is defined as the ratio of global solar irradiance measured at ground level G and its counterpart estimated at the top of the atmosphere Gext (Liu and Jordan, 1960):(9.3)kt=GGext.
How to calculate the monthly average clearness index?
The following equation defines the monthly average clearness index: where: Have = the monthly average radiation on the horizontal surface of the earth [kWh/m2/day] Ho,ave
Is the clearness index a dimensionless number?
The clearness indexis a dimensionless number between zero and one, indicating the fraction of the solar radiation striking the top of the atmosphere that makes it through the atmosphere to strike the Earth’s surface. The following equation defines the monthly average clearness index:
What’s the average clearness index of the Sun?
In other words, it is the proportion of the extraterrestrial solar radiation that makes it through to the surface. It varies from around 0.8 in the clearest conditions to near zero in overcast conditions. The monthly average clearness index may vary from near 0.8 down to maybe 0.2.
What does Homer use the clearness index for?
There’s nothing arbitrary about HOMER’s use of the clearness index. The clearness index has a very simple definition. It is equal to the global solar radiation on the surface of the earth divided by the extraterrestrial radiation at the top of the atmosphere.