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).
In 2013, Eppley introduced the ISO 9060 Secondary Standard SPP Pyranometer to replace the venerable PSP. For 2014, the design team was tasked with making a pyranometer targeted for the PV/CSP Industry that was “as good or better at a lower cost” and the GPP was introduced in 2015.
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 GPP measurements to component sum derived values (using an AHF and 8-48) show the GPP is capable of hourly averages better than 2% and daily averages better than 1%.