IEC 61853-1

Uncertainly analysis for G-T matrix measurement in accordance with IEC 61853-1

The G-T matrix measurement in accordance with IEC 61853-1 [1] determines the electrical performance of a PV module under variable module temperature (T) and irradiance (G). As shown in Table 8 the characterization is composed of I-V measurements at 22 test conditions.

	PV module temperature (T)
Irradiance (G)	15°C	25°C	50°C	75°C
100 W/m²	•	•	N/A	N/A
200 W/m²	•	•	N/A	N/A
400 W/m²	•	•	•	N/A
600 W/m²	•	•	•	•
800 W/m²	•	•	•	•
1000 W/m²	•	• (STC)	•	•
1100 W/m²	N/A	•	•	•

Table 8: Test conditions for G-T matrix measurement

(G-T) matrixes of PV module performance parameters (P_max, I_sc and V_oc) are resulting from I-V measurements for each test condition and measurement uncertainties result from the procedures described in section 3.

It must be noted that the contributions from uncertainty sources may change with varying module temperature and irradiance, resulting in specific uncertainty tables for parameters P_max, I_sc and Voc. On the other hand, some contributions from uncertainty sources are highly correlated for all G-T matrix elements (i.e. Irradiance uncertainty from the reference). The following points must be considered individually for each G-T matrix element for the uncertainty analysis:

• Irradiance non-uniformity: The irradiance non-uniformity in the test area of a solar simulator usually changes with the lamp power or by using attenuator masks. A contribution to measurement uncertainty arises from the fact that the average irradiance in the module area may deviate from the irradiance measured at the location of the reference cell. Compensation may be required by adjusting the scaling factor of the reference cell.
• Uncertainty related to irradiance setting: High precision reference cells of “Word PV Scale (WPVS) design” are not designed for operation in high ambient temperature environment. To avoid degradation, the reference cell is preferably held constantly at 25°C. This can be achieved either by placing it outside the temperature chamber (in which the test module is installed) or by active cooling (e.g. Peltier element). In the first case an uncertainty contribution arises from the transfer of calibration to the new position outside the test chamber.
• Temperature measurement uncertainty: Infrared temperature sensors, which are typically used for PMAX measurement under STC, may not be suitable for operation in a high temperature environment. An uncertainty contribution results from the use of contact sensors such as Pt100 or thermocouples. In case of incomplete thermal stabilization, the measured temperature will not correspond to the module junction temperature and this difference between measured temperature and junction temperature constitutes an uncertainty contribution.
• Temperature non-uniformity: If a temperature chamber is used, depending on the air circulation conditions, uncertainty contributions can result from a higher temperature non-uniformity in the PV module area compared to STC measurements. Uncertainties related to temperature non-uniformity will also arise when heating is achieved by continuous light exposure (i.e. steady-state solar simulator).
• Spectral mismatch uncertainty: Spectral responsivity of the PV module under test changes with operating temperature. Furthermore, if a temperature chamber is used, the spectral transmittance of the glass cover at the light entrance side will have an impact on the spectral irradiance reaching the PV module. Both effects are combined within spectral mismatch uncertainty.

References

[1] IEC 61853-1:2011 “Photovoltaic (PV) module performance testing and energy rating - Part 1: Irradiance and temperature performance measurements and power rating”