Solar Radiation• The sun is a gaseous body composed mostly of hydrogen

• Gravity causes intense pressure and heat at the core initiating nuclear fusing reactions

• This means that atoms of lighter elements are combined into atoms of heavier elements, which releases enormous quantities of energy

• Even when planet Earth is 93 million miles away, we still received an amazing quantity of usable energy from the sun.

• Considering 25% efficient PV modules, if we used 1% of the surface of the earth we could meet 29 times our current total energy demand –These some rough calculations I did, but I’ll be glad to discuss your numbers if you happen to get something different.

Solar Radiation• Solar irradiance is the intensity of solar power, usually expressed in Watts per square meter [W/m^2]

• PV modules output is rated based on Peak Sun (1000 W/m^2).

• Since the proportion of input/output holds pretty much linearly for any given PV efficiency, we can very easily evaluate a system performance check by measuring irradiance and the PV module output.

• The amount of radiation received is proportional to the inverse of the square of the distance from the source –that is, twice the distance ¼ of the energy, four times the distance 1/16 and so on

• Solar irradiation is simply the solar irradiance multiplied by time. It is measured in Watt-hours per square meter [Wh/m^2]

Solar Radiation

Solar Radiation

Solar Radiation• Solar Spectrum most the energy received from the sun is electromagnetic radiation in the form of waves.

• Electromagnetic Spectrum is the range of all types of electromagnetic radiation, based on wavelength.

Solar Radiation• Atmospheric Effects: Solar radiation is absorbed,

scattered and reflected by components of the atmosphere

• The amount of radiation reaching the earth is less than what entered the top of the atmosphere. We classify it in two categories:

1. Direct Radiation: radiation from the sun that reaches the earth without scattering

2. Diffuse Radiation: radiation that is scattered by the atmosphere and clouds

Solar Radiation

Solar Radiation• Air Mass represents how much atmosphere the solar radiation has to pass through before reaching the Earth’s surface

• Air Mass (AM) equals 1.0 when the sun is directly overhead at sea level. AM = 1/ Cos Өz

• We are specifically concerned with terrestrial solar radiation –that is, the solar radiation reaching the surface of the earth.

• At high altitudes or in a very clear days, Peak Sun may be more than 1000 W/m^2 but it is a practical value for most locations

• Peak Sun Hours is the number of hours required for a day’s total radiation to accumulate at peak sun condition.

Solar Radiation• Zenith is the point in the sky directly overhead a particular location –as the Zenith angle Өz increases, the sun approaches the horizon. AM = 1/ Cos Өz•

Solar Radiation• Example problem of Peak sun hours per day:

If during the day we have 4 hours at 500 Wh/m^2 and 6 hours at 250 Wh/m^2 we should compute the peak sun hours per day as follow:

First, multiply 4hs x 500 W/m^2 and add to it 6hs x 250 W/m^2 – This will equal 3500 Wh/m^2

Second, we know that by definition Peak Sun is 1000 W/m^2, so if we divide the total irradiation for the day by Peak Sun we will obtain Peak Sun hours. – That is,

Peak Sun Hours = Total Irradiation [Wh/m^2] / Peak Sun [W/m^2] = Peak Sun hours

In our specific problem:

Peak Sun Hours = 3500 Wh/m^2 / 1000 W/m^2 = 3.5 Peak Sun hours

• Note: most solar irradiation data is presented in Peak Sun Hours units

Solar Radiation• Insolation; this is an equivalent term for solar irradiation and can be expressed in KWh/m^2/day or peak sun hours

Solar Radiation

• Solar spectral distribution is important to understanding how the PV modules that we’re going to utilize respond to it

• Most Silicon based PV devices respond only to visible and the near infrared portions of the spectrum

• Thin film modules generally have a narrower response range

Solar Radiation

Solar Constant:- Solar constant is the energy from the sun, per unit time, received on a unit area of surface perpendicular to the radiation, in space, at earth’s mean distance from the sun.According to Thekaekara and Drummond (1971) the value of the solar constant is 1353 W /m2 (1.940 Cal/cm2 min, or 487kJ/ m2 hr).Beam Radiation:- The solar radiation received from the sun without change of direction is called the beam radiation.Diffuse Radiation:- It is the solar radiation received from the sun after its direction has been changed by reflection and scattering by the atmosphere.

• Air Mass:- It is the path length of radiation through the atmosphere, considering the vertical path at sea level as unity.

• Zenith Angle:- It is the angle between the beam from the sun and the vertical.

• Solar Altitude:- It is the angle between the beam from the sun and horizontaI.i.e (90-Zenithangle)

• Solar or Short wave Radiation:- -It is the radiation originating from the sun, at a source temperature of about 60000 K and in the wave length range of 0.3 to 3.0 µm.

• Long wave Radiation:- Radiation originating from sources at temperatures near ordinary ambient temperatures and thus substantially at all wave length greater than 3.0 µm.

• Declination:- It is the angular position of the sun at solar noon with respect to the plane of equator (north positive)

Collectors in Various Ranges and Applications 1. Flat plate Collector(Low temperature t = 1000 C):-• (i). Water heating (ii). Space Heating (iii). Space

Cooling (iv). Drying.2. Cylindrical Parabola (Medium temperature t =

1000 C to 2000 C):- • (i). Vapour engines and Turbines(ii). Process Heating

(iii). Rfrigeration (iv) Cookig.3. Parabolloid Mirror arrays (High Temperaturet

>2000 C):- (i) Steam engines and Turbines(ii) Stirling engine (iii). Thermo-electric generator.