EN IEC 62788-1-4 Measurement Procedures for Materials Used in Photovoltaic Modules - Part 1-4: Capsules - Measurement of Optical Transmittance and Calculation of Solar Weighted Photon Transmittance, Yellowness Index and UV Cut-off Wavelength

The basis of a European standard, later published by the International Electrotechnical Commission (IEC), “EN IEC 62788-1-4 Measurement procedures for materials used in photovoltaic modules - Part 1-4: Encapsulations - Measurement of optical transmittance and calculation of solar weighted photon transmittance, yellowness index and UV cut-off wavelength” describes a method for measuring the optical transmittance of encapsulating materials used in photovoltaic (PV) modules.

The standardized measurements in this procedure quantify the expected transmittance of the encapsulation to the PV cell. Subsequent calculation of the solar weighted transmittance allows comparisons to be made between different materials. The results for unweathered material can be used in an encapsulation manufacturer's data sheets, in the manufacturer's material or process development, in production quality control (material acceptance), or applied in the analysis of module performance.

This measurement method can also be used to monitor the performance of encapsulation materials after exposure to weathering to help assess their durability. Standardized measurements are designed to examine an interior region within a PV module, for example, without the effects of oxygen diffusion around the cells. Subsequent calculation of the yellowness index allows durability to be quantified and appearance to be taken into account. Changes in transmittance, yellowness index, and ultraviolet (UV) cutoff wavelength can be used by encapsulation or module manufacturers to compare the durability of different materials.

For the purposes of this standard, the following terms and definitions apply:

• The solar weighted transmittance of photon irradiance expresses the fraction of solar spectral photon irradiance optically transmitted from the sample over the entire range of the terrestrial solar spectrum (280 nm to 2 500 nm). Photon irradiance describes the wavelength specific energy of the optical flux and should not be confused with spectral irradiance.
• Representative solar weighted photon irradiance transmittance expresses the ratio of solar spectral photon irradiance optically transmitted from the sample over the range of the terrestrial solar spectrum (300 nm to 1250 nm). In the case of a PV device, representative solar weighted photon irradiance transmittance is defined over the range of the spectrum used by a representative PV device (which may not include wavelengths as low as 280 nm or as high as 2 500 nm).
• The UV cutoff wavelength refers to the wavelength of light at which the encapsulation is considered optically absorbing and the encapsulation is transmissive. In this procedure, 10 percent absolute transmittance is considered the threshold for the UV cutoff wavelength. The UV cutoff wavelength can also be used to measure the effects of corrosion.
• Abrasion refers to the process of exposing samples to environmental conditions that may include ultraviolet radiation, temperature, humidity, and ozone. Abrasion can occur in artificial or natural environments. Abrasion can occur at a nominal (field) or accelerated rate.
• The yellowness index refers to the calculated value that describes the yellowness of the test sample as perceived by the human observer. This value can be used to measure the effects of weather conditions.

In principle, the total spectral transmittance of laminated samples containing encapsulation material is measured using a spectrophotometer equipped with an integrating sphere. The solar weighted transmittance, yellowness index and UV cut-off wavelength are then calculated from the transmittance measurements. The transmittance measured using this procedure can be used in more advanced optical analysis to improve the accuracy of the PV performance analysis or to distinguish between different encapsulation materials, as described in the standard appendix (Annex A). The transmittance measured using this procedure can be used to estimate module performance (current efficiency) if the quantum efficiency of the PV cell is known, as described in Annex B. The method does not attempt to account for changes in transmittance with the angle of incidence, which can vary with time of day, sky conditions and module geometry, particularly if optical concentration is used.

The test apparatus used in these tests consists of a dual-beam spectrophotometer equipped with an integrating sphere. If the port reflectance can be calculated appropriately, a single-beam spectrophotometer may be used. Details on the construction and configurations of the test apparatus are contained in ISO 13468-2 or ASTM E424-71. A measurement range of at least 60904 nm to 3 nm is required for the calculation of solar-weighted transmittance using the AM1.5 spherical spectrum as in IEC 280-2. A wavelength increment of no greater than 500 nm is preferred for the measurement, but increments up to 1 nm with linear interpolation up to 1 nm are permitted. To reduce measurement error, an integrating sphere of at least 5 mm in diameter with a port area of ​​at least 5 percent is recommended.

Our organization has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. Among the numerous test, measurement, analysis and evaluation studies provided for businesses in various sectors, there are also test services in accordance with the standard “EN IEC 62788-1-4 Measurement procedures for materials used in photovoltaic modules - Part 1-4: Capsules - Measurement of optical transmittance and calculation of solar weighted photon transmittance, yellowness index and UV cut-off wavelength”.