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solar_uv_interface [2020/03/27 09:15]
tedem [Overview]
solar_uv_interface [2020/03/29 12:45]
tedem [Additional Information]
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 Accurate calibration of a pyranometer is challenging even with expensive specialist equipment so we have to be realistic about what can be achieved. Commercial solar sensors are generally supplied with a calibration traceable to a national standard, which is one reason they are so expensive. If bought as a complete unit, the sensitivity of the WeatherDuino solar sensor will have been adjusted to provide an approximate calibration. This means that under ideal conditions the solar irradiance measured by the WeatherDuino solar sensor should be similar to the theoretical maximum value, taking into account the latitude and longitude of the site, the time and the date. 'Ideal conditions'​ in this context means a cloudless day with excellent visibility, and the best time to make the comparison is around noon in mid-summer. The Sun's rays travel through the minumum thickness of atmosphere at noon in mid-summer, and the rate of change of the solar incident angle is least around noon, so irradiance values are relatively stable. Accurate calibration of a pyranometer is challenging even with expensive specialist equipment so we have to be realistic about what can be achieved. Commercial solar sensors are generally supplied with a calibration traceable to a national standard, which is one reason they are so expensive. If bought as a complete unit, the sensitivity of the WeatherDuino solar sensor will have been adjusted to provide an approximate calibration. This means that under ideal conditions the solar irradiance measured by the WeatherDuino solar sensor should be similar to the theoretical maximum value, taking into account the latitude and longitude of the site, the time and the date. 'Ideal conditions'​ in this context means a cloudless day with excellent visibility, and the best time to make the comparison is around noon in mid-summer. The Sun's rays travel through the minumum thickness of atmosphere at noon in mid-summer, and the rate of change of the solar incident angle is least around noon, so irradiance values are relatively stable.
  
-The theoretical maximum solar irradiance for any location at any day of the year can be found using the Apogee [[http://​clearskycalculator.com/​pyranometer.htm|Clear Sky Calculator]] or, if you are using the Cumulus MX software it is shown on the same chart as the measured solar irradiance.+The theoretical maximum solar irradiance for any location at any day of the year can be found using the Apogee [[http://​clearskycalculator.com/​pyranometer.htm|Clear Sky Calculator]] or, if you are using the Cumulus MX software it is shown on the same chart as the measured solar irradiance. Any mismatch between the theoretical maximum and that measured can reduced by adjusting the scaling factors in the Cumulus software. Note, however, that occasional values in excess of the theoretical maximum are possible, especially at the edges of clouds where the irradiance may be enhanced.
  
  
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