Operators of photovoltaic systems expecttheir system to function reliably for maxi-mum electricity yield.

To monitor the correct functioning ofphotovoltaic systems, it is advisable tocontinuously measure the solar irradi-ance using irradiance sensors.

Solar irradiance sensors which corre-spond in their construction to a photo-voltaic module are preferably used.Consequently, solar irradiance sensorsare often composed of a solar cell andmeasuring electronics determining theshort-circuit current of this solar cell.

The irradiance sensitivity is then used toconvert the short-circuit current into thecorresponding irradiance. Thus, the irra-diance sensitivity of the radiation sensoris one of the most important influencingfactors for correct monitoring of the solarirradiance and needs to be determinedduring calibration of the sensor.

In the solar cell calibration laboratory ofthe Calibration and Test Center (CalTeC)of the Institute for Solar Energy Research(ISFH) we perform a DAkkS accreditedcalibration of solar irradiance sensors.

Calibration of Solar Irradiance Sensors

Dr. Karsten Bothe & Dr. David Hinken

eMail solarcells@caltec.isfh.deInternet www.caltec.isfh.de

Institut für Solarenergieforschung GmbHCalibration and Test CenterSolar Cells and SensorsAm Ohrberg 1 31860 EmmerthalGermany

Calibrated measurement of the spectral responsivity sSTC.rel() of a solar irradiance

sensor under standard testing conditions (STC) andassociated measurement uncertainty U

The calibration of solar irradiance sensors is car-ried out under standard testing conditions at atemperature of 25°C and the AM1.5G referencespectrum at an irradiance of 1000 W/m2.

Since irradiance sensors are usually not activelycooled, they heat up under real operation condi-tions. Therefore our calibration always includesthe determination of the responsivity as a func-tion of temperature.

For this purpose, the sensor is illuminated withthe light of an AAA sun simulator and the outputsignal of the irradiance sensor is measured as afunction of temperature between 23 and 75°Cusing the built-in temperature sensor.

If the output signal of the sensor does notchange linearly with the irradiance, a calibrati-on at different irradiance levels need to beperformed. For this purpose we offer calibrati-ons at 100, 500 and 1000 W/m2.

To obtain highest precision we also recomand aspectral mismatch correction. For this purposewe measure the spectral responsivity s() as afunction of wavelength .

This measurement requires a sensor withoutmeasuring electronics or measuring resistor.Alternatively, it can be carried out on a sensorof identical construction.

Calibration of Solar Irradiance Sensors

Calibrated measurement of the responsivity s of a solar irradiance sensor

as a function of temperature T