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The SI unit of irradiance is watts per square metre (W/m 2 = Wm −2). The unit of insolation often used in the solar power industry is kilowatt hours per square metre (kWh/m 2). [12] The Langley is an alternative unit of insolation. One Langley is one thermochemical calorie per square centimetre or 41,840 J/m 2. [13]
The angular diameter of the Earth as seen from the Sun is approximately 1/11,700 radians (about 18 arcseconds), meaning the solid angle of the Earth as seen from the Sun is approximately 1/175,000,000 of a steradian. Thus the Sun emits about 2.2 billion times the amount of radiation that is caught by Earth, in other words about 3.846×10 26 watts.
Multiplying the figure of 1,050 watts per square meter by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98,000 lux (lumens per square meter) on a perpendicular surface at sea level. The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky.
watt per square metre per hertz W⋅m −2 ⋅Hz −1: M⋅T −2: Radiosity of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅m −2 ⋅nm −1. This is sometimes also confusingly called "spectral intensity". J e,λ [nb 4] watt per square metre, per metre W/m 3: M⋅L −1 ⋅T −3: Radiant exitance: M e ...
The two forms have different dimensions and units: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W⋅m −2 ⋅Hz −1), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W⋅m −3), or more commonly watts per square metre per nanometre (W⋅m −2 ...
Radiant intensity, a radiometric quantity measured in watts per steradian (W/sr) Luminous intensity, a photometric quantity measured in lumens per steradian (lm/sr), or candela (cd) Irradiance, a radiometric quantity, measured in watts per square meter (W/m 2) Intensity (physics), the name for irradiance used in other branches of physics (W/m 2)
where Pd is the power density in watts per square meter (one W/m 2 is equal to 0.1 mW/cm 2), H 2 = the square of the value of the magnetic field in amperes RMS squared per meter squared, E 2 = the square of the value of the electric field in volts RMS squared per meter squared. [6]
In 2015, three solar farms were constructed in the Philippines. The Philippines receives over 7kWh per square meter per day during its peak month of April and lowest at 3kWH per square meter per day during its off-peak month of December as observed by Schadow1 Expeditions in 33 cities of the country. [10]