A pyranometer is used to measure the energy from the sun. When leveled in the horizontal plane, this is called the Global Shortwave Irradiance (GLOBAL) and when positioned in a plane of a PV Array, it is called the Total Irradiance in the plane of array (TPA). Inverted, a pyranometer is used to measure the Reflected or Albedo Irradiance (ALBEDO). A pyranometer can also be shaded from the direct beam of the sun to measure the Diffuse Shortwave Irradiance (DIFFUSE).
Based on the design of the distinguished PSP Pyranometer, the new SPP has faster response time, a reduced nighttime thermal offset, an improved cosine response and a better temperature dependence. This makes the SPP the ideal instrument for high quality network measurements and as a transfer standard for calibration of other pyranometers. A thermistor is included for measuring instrument temperature.
Recently, there has been much discussion on “uncertainty” and how it pertains to solar measurements. The RSS of the 9060 Secondary Standard specifications results in an uncertainty of approximately 3.5%. The typical uncertainty of Eppley’s factory calibrations are less than 1%. The stated uncertainty of the WRR is 0.4%. Evidence from comparisons of SPP measurements to component sum derived values (using an AHF and 8-48) show the SPP is capable of hourly averages better than 2% and daily averages better than 1%.