Reporting back from the NREL Pyrheliometer Comparison 2013

Accurate measurement of direct solar irradiance is essential in the fields of meteorology, climatology and solar energy. To achieve this scientists use pyrheliometers, instruments that measure the direct solar irradiance within a 5° field of view and are mounted on an automatic tracker to point precisely at the centre of the sun. There are two main types of pyrheliometers. Absolute cavity radiometers do not usually have a window, have a shutter to block the incoming radiation, and are connected to a control unit and computer. Field pyrheliometers operate autonomously, have a window, and are designed for continuous all-weather use – like our CHP 1 and SHP1 models.

Our pyrheliometers have a calibration that is traceable to the international standard for direct solar irradiance measurement, the World Radiometric Reference (WRR). This is realised by the World Standard Group (WSG) of radiometers at the World Radiation Center ( PMOD-WRC) in Davos, Switzerland. To ensure WRR traceability, and to maintain a high level of quality, Kipp & Zonen regularly participates in pyrheliometer comparisons, such as the International Pyrheliometer Comparison (IPC) in Davos and the NREL Pyrheliometer Comparison (NPC) in Golden, Colorado.

This September we participated in the 17th annual NPC at the Solar Radiation Research Laboratory in Golden. At the NPC we operated 4 field pyrheliometers mounted on a SOLYS 2 sun tracker and our PMO6-cc absolute cavity pyrheliometer.

In total more than 34 scientists and engineers, operating more than 52 instruments, participated in comparing direct solar irradiance measurements. These measurements resulted in a calibration to the NREL group of pyrheliometers, which is traceable to the WRR.

The full official report from the NREL Pyrheliometer Comparison 2013 is expected in the beginning of 2014.

The report of 2012 is downloadable.