Photovoltaic (PV) modules, operate at high voltages and elevated temperatures, and are known to degrade because of leakage current to ground. Related degradation processes may include: electric/ionic corrosion, electrochemical deposition, electromigration, and/or charge build-up in thin layers. The use of polymeric materials with a high resistivity is known to reduce the rate of potential induced degradation processes. Because of this, PV materials suppliers are placing increased importance on the encapsulant bulk resistivity, but there is no universally accepted method for making this measurement. The development of a resistivity test standard is described in this paper. We have performed a number of exploratory and round-robin tests to establish a representative and reproducible method for determining the bulk resistivity of polymeric materials, including encapsulation, backsheet, edge seals, and adhesives. The duration of measurement has been shown to greatly affect the results, e.g., an increase as great as 100X was seen for different measurement times. The standard has been developed using measurements alternating between an "on" and "off" voltage state with a weighted averaging function and cycle times of an hour.
Although the main root causes and referring counter measures for PID are known, a significant part of the industrial modules are still found to be PID sensitive in testing and PID is increasingly evident in field. This paper discusses field occurrence of PID with respect to environmental conditions and material properties. Different PID pattern in field and in test are analyzed in terms of the potential distribution and surface conductivity. Examples are given for the correlation of PID lab tests of a (commercial) BOM with real outdoor degradation. PID progress is predicted for different locations and compared with measurement data. Suitable quality control measures are discussed for the modules as well as for the encapsulation material
We examine a proposed test standard that can be used to evaluate the maximum representative change in linear dimensions of sheet encapsulation products for photovoltaic modules (resulting from their thermal processing). The proposed protocol is part of a series of material-level tests being developed within Working Group 2 of the Technical Committee 82 of the International Electrotechnical Commission. The characterization tests are being developed to aid module design (by identifying the essential characteristics that should be communicated on a datasheet), quality control (via internal material acceptance and process control), and failure analysis. Discovery and interlaboratory experiments were used to select particular parameters for the size-change test. The choice of a sand substrate and aluminum carrier is explored relative to other options. The temperature uniformity of ±5°C for the substrate was confirmed using thermography. Considerations related to the heating device (hot-plate or oven) are explored. The time duration of 5 minutes was identified from the time-series photographic characterization of material specimens (EVA, ionomer, PVB, TPO, and TPU). The test procedure was revised to account for observed effects of size and edges. The interlaboratory study identified typical size-change characteristics, and also verified the absolute reproducibility of ±5% between laboratories.
We proposed an UV accelerated test condition for an EVA encapsulant, based on analysis of long term field exposed PV
modules. We found that strong UV irradiation into EVA encapsulant test sample led to the fast decomposition of UV
absorber formulated in EVA encapsulant, which has never seen in the field exposed PV modules. Thus, the integrating
UV intensity of 60 W/m2 and black panel temperature of 110°C using a xenon weather-o-meter were suitable as an UV
accelerated test condition. With this proposed test condition, which shows that 1 week exposure by xenon light
corresponds to 1 year field exposure, we can predict discoloration rate of EVA encapsulant.
In addition, we evaluated change in peel strength to glass for Mitsui's and the other commercially available EVA
encapsulants during UV accelerated test with the proposed condition. There was no large change in peel strength for our
EVA encapsulant during the UV accelerated test. On the other hand, we observed that the competitor's EVA encapsulant
showed the large decrease of peel strength to glass at early stage, even no change in yellowness index (YI). This result
indicates not only YI change but also peel strength change should be evaluated for design of reliable PV module and
We have developed "tapered self-written waveguide (SWW)" for coupling of optical components in the board level optical interconnection. Tapered waveguides have a possibility of achieving larger alignment tolerance for optical coupling. The fabrication condition of tapered SWW was studied by adjusting both the optical power and irradiation time of curing resin, and tapered SWW was successfully realized. The optical tolerance vertical to the optical axis twice as compared with straight SWW was obtained.
In the optical interconnection of board level, 45-degree micro mirrors are used to achieve 90-degree optical path change. These mirrors are often fabricated by using a rotating blade and this method has a serious problem of cutting other waveguides in the vicinity. A self-written waveguide ha been successfully applied to repari and connect these waveguides. So, it will be possible to allow optical signals to be input and output at a specific location on the board.
A micro-mirror formed using excimer laser processing for a fluorinated polyimide waveguide film was demonstrated. The tilted excimer laser irradiation to the waveguide core formed a micro-mirror with an angle of 45 +/- 1-degree. The micro-mirror had convex profile and exhibited a lens effect as a concave mirror. The micro-mirror, as formed, exhibited a low reflection loss of approximately 0.6dB at a wavelength of 850nm. This technique applied to flexible optical and electrical circuit board.
Replication processes of a fluorinated polyimide film were demonstrated using a polyimide and a quartz glass molds. A silicon-oxide was introduced on the top of the mold, which could significantly improve the separation between the mold and the fluorinated polyimide film without degrading the optical property. A single- and a multimode waveguide film were fabricated using a cladding film with grooves formed by our replication process. The multimode waveguide exhibited low optical propagation loss of 0.36dB/cm at the wavelength of 0.85um. Using the fluorinated polyimide waveguide film, a low cost optical board with vertical-cavity surface-emitting laser (VCSEL) and photodiode (PD) was developed for intra-board level optical interconnection. The edges of the multimode waveguide film were butt-coupled to a commercialized 0.85um multimode VCSEL and PD by the passive alignment technique developed. The waveguide film coupled with the VCSEL and the PD was mounted on a FR-4 printed wiring board (PWB), bending the waveguide film. The total loss of two couplings between the waveguide and optical components (VCSEL and PD) was obtained to be less than 3 dB. We confirmed that the high-bit-rate data, >3Gbps, was transmitted using the optical board on the PWB.
A replication process using a SiO2 mold was demonstrated using a fluorinated polyimide. The replicated fluorinated polyimide film was separated from the mold by soaking in distilled water. The film separation with slow and then successive fast steps was due to the displacment of the weak adhesive layer by water and release of stress at the interface, respectively. Lowering the curing temperature of the fluorinated polyimide, whcih formed the weak adhesive layer at the interface, improved separation without chipping of the stripes of the SiO2 mold.