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Solar radiation maps are built using databases derived from satellite imagery, as for example using visible images from Meteosat Prime satellite. A method is applied to the images to determine solar radiation. One well validated satellite-to-irradiance model is the SUNY model. [39] The accuracy of this model is well evaluated.
The solar constant includes radiation over the entire electromagnetic spectrum. It is measured by satellite as being 1.361 kilo watts per square meter (kW/m 2) at solar minimum (the time in the 11-year solar cycle when the number of sunspots is minimal) and approximately 0.1% greater (roughly 1.362 kW/m 2) at solar maximum. [1]
For example, a solar panel with 20% efficiency and an area of 1 m 2 produces 200 kWh/yr at Standard Test Conditions if exposed to the Standard Test Condition solar irradiance value of 1000 W/m 2 for 2.74 hours a day. Usually solar panels are exposed to sunlight for longer than this in a given day, but the solar irradiance is less than 1000 W/m ...
The illuminance for Daylight (this version) under AM1.5 is given as 109,870 lux (corresponding with the AM1.5 spectrum to 1000.4 W/m 2). AM2~3; AM2 (=60°) to AM3 (=70°) is a useful range for estimating the overall average performance of solar cells installed at high latitudes such as in northern Europe. Similarly AM2 to AM3 is useful to ...
Of the ~340 W/m 2 of solar radiation received by the Earth, an average of ~77 W/m 2 is reflected back to space by clouds and the atmosphere and ~23 W/m 2 is reflected by the surface albedo, leaving ~240 W/m 2 of solar energy input to the Earth's energy budget. This amount is called the absorbed solar radiation (ASR).
If the extraterrestrial solar radiation is 1,367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1,050 W/m 2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1,120 W/m 2. [6]
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 . Irradiance is often called intensity , but this term is avoided in radiometry where such usage leads to confusion with radiant intensity .
Solar activity has been on a declining trend since the 1960s, as indicated by solar cycles 19–24, in which the maximum number of sunspots were 201, 111, 165, 159, 121 and 82, respectively. [14] In the three decades following 1978, the combination of solar and volcanic activity is estimated to have had a slight cooling influence. [ 15 ]