psk-solar introductiont presentation
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power sysiemTRANSCRIPT
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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.
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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]
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Solar Radiation
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Solar Radiation
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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.
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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
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Solar Radiation
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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.
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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•
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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
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Solar Radiation• Insolation; this is an equivalent term for solar irradiation and can be expressed in KWh/m^2/day or peak sun hours
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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
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Solar Radiation
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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.
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• 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)
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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.