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What Is Solar Radiation? How To Control Solar Radiation

What Is Solar Radiation? How To Control Solar Radiation


At this Blog post you will learn about various map of Solar radiation in the worlds, so you will able to more understand the radiation map of solar in the worlds. The solar energy impinging the surface of the earth is depicted below 
Basics of Solar Radiation
Radiation from the sun sustains life on earth and determines climate. The energy flow within the sun results in a surface temperature of around 5800 K, so the spectrum of the radiation from the sun is similar to that of a 5800 K blackbody with fine structure due to absorption in the cool peripheral solar gas (Fraunhofer lines).
This divides the world into five solar performance area based on yearly averages of daily hours of sunlight and temperature


Source : Globe Engineering Research
the red area is most powerful for Solar radiation power generation,
everyday there is plenty of energy from the sun hitting the earth but today those energy still doesn't have priority at the worlds, picture below taken from Nate Lewis of the California Institute of Technology, shown that six solar radiation power plant can produce about 20 Tera watts of electrical power. That would totally solve humanity's energy problem.

after we know the total energy average per years, we should known where is the total yearly energy capture potential of the site that determines the economical viability of installing a power plant.
 
this map have same with previous but more clearly and this map is for Solar thermal energy map, not solar radiation,

How does solar radiation affect the temperature of a roof surface and heat flow through the roof?


This solar radiation control fact sheet focuses on low-slope roofs for commercial buildings. The membranes or weatherproofing materials used for these roofs are opaque to solar radiation. When opaque roof surfaces are exposed to solar radiation, no solar radiation is directly transmitted through the roof. The sketch above in the heading depicts an opaque low-slope roof interacting with solar radiation. It illustrates that some of the sunlight is reflected away by the surface and the rest is absorbed. The fraction reflected is given by the solar reflectance of the surface, a number between 0 and 1 that applies to the solar part of the electromagnetic spectrum. Solar radiation includes the wavelength range from near ultraviolet to near infrared, spanning what is visible to the human eye. The sketch assumes a solar reflectance of about 0.85.
The solar radiation that is absorbed heats the surface. The absorbed energy is no longer solar energy. It is characterized by the temperature of the surface material, which is much lower than the equivalent solar temperature. Consequently, the surface emits radiation in the far infrared part of the spectrum. This infrared radiation is not to be confused with the reflected solar radiation. The amount emitted is in direct proportion to the surface's infrared emittance, a number between 0 and 1 that is generally different from the solar reflectance. A roof surface also exchanges energy by convection with the air above the roof and by conduction with the layer of the roof directly below the surface. Moisture effects, mainly evaporation and condensation of liquid water on the surface, are occasionally important for low-slope roofs.

The temperature of the roof surface is determined by a balance among energy gains and losses, including energy stored in the roof. The peak surface temperature strongly depends on the peak solar radiation and the solar reflectance of the surface. On a sunny day in late June, all of July or early August in the northern hemisphere, a black roof surface (solar reflectance less than 0.1) may reach peak temperatures exceeding 170°F (77°C). At the same time, a highly reflective white surface (solar reflectance greater than 0.8) could be less than 110°F (43°C).
For steady conditions, heat flow per unit area through a roof is given by the quotient of the temperature difference across the roof and the total thermal resistance of the roof. On a cloud-free day in the middle of summer for typical inside surface temperatures of 80°F (27°C), solar radiation control causes a decrease in the temperature difference across the roof from about 90°F to 30°F (from about 50°C to 17°C). If the total thermal resistance (R-value) of the materials present in the roof is small, a significant decrease in steady heat flux through the roof will occur. If the roof has significant thermal capacitance (thermal mass), absorbed energy will be stored in the roof and heat fluxes through the roof will be delayed and diminished, lessening the effect of solar radiation control. Cloudiness and other non-steady conditions also decrease the heat flux through the roof relative to the maximum steady value.





1 comment:

  1. congratulations guys, quality information you have given!!! John

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