Engineering topics

Wohlgemuth, J H

Publications and source records attributed to Wohlgemuth, J H.

4 records

DOE OSTI2012

Technology and Climate Trends in PV Module Degradation: Preprint

To sustain the commercial success of photovoltaic (PV) technology it is vital to know how power output decreases with time. Unfortunately, it can take years to accurately measure the long-term degradation of new products, but past experience on older products can provide a basis for prediction of degradation rates of new products. An extensive search resulted in more than 2000 reported degradation rates with more than 1100 reported rates that include some or all IV parameters. In this paper we discuss how the details of the degradation data give clues about the degradation mechanisms and how they depend on technology and climate zones as well as how they affect current and voltage differently. The largest contributor to maximum power decline for crystalline Si technologies is short circuit current (or maximum current) degradation and to a lesser degree loss in fill factor. Thin-film technologies are characterized by a much higher contribution from fill factor particularly for humid climates. Crystalline Si technologies in hot & humid climates also display a higher probability to show a mixture of losses (not just short circuit current losses) compared to other climates. The distribution for the module I-V parameters (electrical mismatch) was found to change with field exposure. The distributions not only widened but also developed a tail at the lower end, skewing the distribution.

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DOE OSTI2012

Standards for PV Modules and Components -- Recent Developments and Challenges: Preprint

International standards play an important role in the Photovoltaic industry. Since PV is such a global industry it is critical that PV products be measured and qualified the same way everywhere in the world. IEC TC82 has developed and published a number of module and component measurement and qualification standards. These are continually being updated to take advantage of new techniques and equipment as well as better understanding of test requirements. Standards presently being updated include the third edition of IEC 61215, Crystalline Silicon Qualification and the second edition of IEC 61730, PV Module Safety Requirements. New standards under development include qualification of junction boxes, connectors, PV cables, and module integrated electronics as well as for testing the packaging used during transport of modules. After many years of effort, a draft standard on Module Energy Rating should be circulated for review soon. New activities have been undertaken to develop standards for the materials within a module and to develop tests that evaluate modules for wear-out in the field (International PV Module QA Task Force). This paper will discuss these efforts and indicate how the audience can participate in development of international standards.

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DOE OSTI2012

Examination of a Junction-Box Adhesion Test for Use in Photovoltaic Module Qualification (Presentation)

Engineering robust adhesion of the junction-box (j-box) is a hurdle typically encountered by photovoltaic (PV) module manufacturers during product development. There are historical incidences of adverse effects (e.g., fires) caused when the j-box/adhesive/module system has failed in the field. The addition of a weight to the j-box during the 'damp heat' IEC qualification test is proposed to verify the basic robustness of its adhesion system. The details of the proposed test will be described, in addition to the preliminary results obtained using representative materials and components. The described discovery experiments examine moisture-cured silicone, foam tape, and hot-melt adhesives used in conjunction with PET or glass module 'substrates.' To be able to interpret the results, a set of material-level characterizations was performed, including thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. PV j-boxes were adhered to a substrate, loaded with a prescribed weight, and then placed inside an environmental chamber (at 85C, 85% relative humidity). Some systems did not remain attached through the discovery experiments. Observed failure modes include delamination (at the j-box/adhesive or adhesive/substrate interface) and phase change/creep. The results are discussed in the context of the application requirements, in addition to the plan for the formal experiment supporting the proposed modification to the qualification test.

14 SOLAR ENERGY↗

DOE OSTI2012

Examination of a Size-Change Test for Photovoltaic Encapsulation Materials (Presentation)

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 +/- 5C 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.

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