Calibration of solar cells with the Direct Sunlight Method at ESTI, JRC

The goals of RMG 2 is to perform calibration measurements of the short circuit current of reference solar cells under Standard Test Conditions (ISTC) [1] from at least two solar cells using the integral solar cell calibration method and to produce an uncertainty budget of this integral solar cell calibration method used at the facility at European Solar Test Installation (ESTI), Joint Research Center (JRC). A set of two unfiltered and one filtered mono c-Si reference solar cells were calibrated, using the primary Differential Spectral Responsivity (DSR) method at PTB and the primary Direct Sunlight Method (DSM) method at ESTI.
The Direct Sunlight Method (DSM) is an integral calibration method for calibration of solar cells (e.g. reference solar cells). Generally, the aim is to determine short circuit current under Standard Test Conditions (ISTC) of the Device Under Test (DUT). The Standard Test Conditions are:

  • Irradiance level ESTC=1000 Wm-2,
  • Temperature T = 25 °C ,
  • and AM1.5G reference spectrum (in according to IEC 60904-3).

The DSM realise the illumination with the direct natural sunlight. In addition to the current measurement of the DUT, the spectrum of the sunlight is measured with an EKO Wiser system, the irradiance level with a pyrheliometer, and the temperature with an integrated temperature sensor. However, even the direct natural sunlight doesn’t match perfectly the reference spectrum AM1.5G. Therefore, a spectral mismatch correction (IEC 60904-7) have to be applied. The spectral mismatch correction require the spectral responsivity of the DUT in addition to the measured direct natural sunlight spectrum.
A set of three solar cells was investigated at PTB and JRC. The research stay was used to transfer knowledge between the researcher and the guest organisation. The evaluation of the results is still in progress.