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Direct normal irradiance (DNI), or beam radiation, is measured at the surface of the Earth at a given location with a surface element perpendicular to the Sun direction. [ 6 ] [ failed verification ] It excludes diffuse solar radiation (radiation that is scattered or reflected by atmospheric components).
Direct normal irradiance spectra calculated with SMARTS 2.9.5 for increasing air mass (0 to 10), using the same atmospheric conditions as the ASTM G173 standard. Air mass 0 corresponds to the extraterrestrial spectrum, [1] marked as Top of Atmosphere (TOA).
Direct insolation is equal to the solar irradiance above the atmosphere minus the atmospheric losses due to absorption and scattering. While the solar irradiance above the atmosphere varies with the Earth–Sun distance and solar cycles , the losses depend on the time of day (length of light's path through the atmosphere depending on the solar ...
Direct neural interface, a brain-computer interface; Direct normal irradiance, a measure of the solar irradiance striking a surface held normal to the line of sight to the sun; Direct normal insolation, also known as direct insolation, a measure of the solar irradiance striking a surface held normal to line of sight to the sun
In radiometry, irradiance is the radiant flux received by a surface per unit area. The SI unit of irradiance is the watt per square metre (symbol W⋅m −2 or W/m 2 ). The CGS unit erg per square centimetre per second (erg⋅cm −2 ⋅s −1 ) is often used in astronomy .
Since 1978, solar irradiance has been directly measured by satellites with very good accuracy. [11]: 6 These measurements indicate that the Sun's total solar irradiance fluctuates by +-0.1% over the ~11 years of the solar cycle, but that its average value has been stable since the measurements started in 1978.
Solar irradiance spectrum above atmosphere and at surface. The overall intensity of solar radiation is like that of a black body radiator of the same size at about 5,800 K. [1] As it passes through the atmosphere, sunlight is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation.
This is typically specified as average DNI (Direct Normal Irradiance) greater than 5.5-6m kWh/m 2 /day or 2000 kWh/m 2 /yr. Otherwise, evaluations of annualized DNI vs. GNI/GHI (Global Normal Irradiance and Global Horizontal Irradiance) irradiance data have concluded that conventional PV should still perform better over time than presently ...