Indoor Testing

The laboratory offers standardised and non-standardised indoor tests. Below is a list of the offered services.

Current-voltage characterisation at standard test conditions (STC)

Measurements are taken indoors under a AAA-class solar simulator1, whilst the cell is held at 25 °C. The illumination is provided in a short flash equivalent to 1-sun intensity at 1000 Wm-2. The current-voltage characteristic is measured through an electronic load. This data is then used to calculate cell parameters such as shunt and series resistances, power, short-circuit current and open circuit voltage under these conditions. A test report is prepared in accordance with ISO 17025.

IEC Standards:

• 60904-1 Measurement of photovoltaic current-voltage characteristics.

Current, voltage and power temperature coefficients

The cells are tested indoors under a AAA-class solar simulator. The cells are mounted on a temperature-controlled chuck, and multiple current-voltage characteristics are taken over a range of temperatures in 10 °C increments and a constant irradiance of 1000 Wm-2. These data are then processed to determine the change of power, short-circuit current and open-circuit voltage with temperature.

IEC Standards:

• 60891 Procedures for temperature and irradiance corrections to measured I - V characteristics of crystalline silicon photovoltaic devices.

Spectral response measurement

The spectral response of a cell can be measured with or without encapsulation by using a solar simulator and measuring the short-circuit current output of a cell under different wavelengths of light. In the case of single-junction cells, spectral filters with a bandpass of 50 nm are used to determine the External Quantum Efficiency (EQE) for each band of wavelengths. In the case of multi-junction cells, a chopped light source along with bias lighting and voltages are applied to investigate the performance of each junction in isolation, typically with a resolution of 5 to 10 nm.

IEC Standards:

• 60904-8 Measurement of spectral response of a photovoltaic (PV) device.

Electroluminescence imaging

Electroluminescence imaging is a useful diagnostic technique that can be used to investigate the structural and electrical integrity of a photovoltaic device. An electronic power supply is used to drive current in through the cell in forward bias. This causes the cell to emit light in the near infrared region, resulting in a spatially-resolved image of conversion efficiency that can be captured by a high-resolution IR camera. Damaged areas of the cell not visible to the naked eye can be easily pinpointed using this technique.

Module performance at standard test conditions (STC)

The modules are mounted in an indoor flash tunnel and a large-area AAA-class solar simulator is used to provide an illumination intensity of 1000 Wm-2 in the plane of the panels whilst they are held at a temperature of 25 °C. The output of the module is measured by an electronic load that measures the current-voltage characteristic of the module, giving the power output, open circuit voltage, short-circuit current, and fill factors. A test report is prepared in accordance with ISO 17025.

IEC Standards:

• 61215 Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval .

• 61646 Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approvalCurrent-voltage characterisation at standard test conditions (STC).

Measurement of module temperature coefficients

For this measurement, temperature sensors are fixed to the middle of the back of the module. A series of current-voltage characterisations are performed at different module temperatures and fixed illumination, and by applying a least-squares fit to the data, power, current and voltage temperature coefficients of the module are determined. In addition, I-V characterisations are performed at a fixed temperature under different irradiance intensities to calculate the series and shunt resistances of the module under test. A test report is prepared in accordance with ISO 17025.

IEC Standards:

• 61215 Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval .

• 61646 Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approval .

• 60891 Procedures for temperature and irradiance corrections to measured I - V characteristics of crystalline silicon photovoltaic devicesCurrent-voltage characterisation at standard test conditions (STC).

Damp heat test

The module under test is introduced into a climatic chamber, and held at a temperature of 85 °C ± 2 °C and relative humidity of 85 % ± 5% for a duration of 1000 hours. Once removed from the chamber, the module is subjected to an insulation test, a wet leakage test, a visual inspection and determination of maximum power is performed in accordance with the relevant qualification standard. A test report is prepared in accordance with ISO 17025.

IEC Standards:

• 61215 Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval .

• 61646 Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approvalCurrent-voltage characterisation at standard test conditions (STC) .

Thermal cycling test

In this test, a module is placed in a climatic chamber, temperature sensors are connected to the centre of the panel, and an electronic power supply connected to the module terminals. The panel is then subjected to 200 cycles where the temperature is raised from -40 °C to + 85 °C in accordance with the figure on the right.

Whilst the module is above 25 °C, current equal to the output at STC conditions is passed through the module, and this is logged along with the module temperature. A test report is prepared in accordance with ISO 17025.

IEC Standards:

• 61215 Crystalline silicon terrestrial photovoltaic (PV) modules – Design qualification and type approval .

• 61646 Thin-film terrestrial photovoltaic (PV) modules – Design qualification and type approvalCurrent-voltage characterisation at standard test conditions (STC).

Indoor Testing

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