Search NASA⌕ Search

Engineering topics

Wohlgemuth, J

Publications and source records attributed to Wohlgemuth, J.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Technology and Climate Trends in PV Module Degradation (Presentation)

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 presentation 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.

14 SOLAR ENERGY↗
DOE OSTI2012

Field Evaluation of the Potential for Creep in Thermoplastic Encapsulant Materials: Preprint

There has been recent interest in the use of thermoplastic encapsulant materials in photovoltaic modules to replace chemically crosslinked materials, e.g., ethylene-vinyl acetate. The related motivations include the desire to: reduce lamination time or temperature; use less moisture-permeable materials; use materials with better corrosion characteristics or with improved electrical resistance.However, the use of any thermoplastic material in a high-temperature environment raises safety and performance concerns, as the standardized tests currently do not expose the modules to temperatures in excess of 85 degrees C, though fielded modules may experience temperatures above 100 degrees C. Here we constructed eight pairs of crystalline-silicon modules and eight pairs ofglass/encapsulation/glass thin-film mock modules using different encapsulant materials of which only two were designed to chemically crosslink. One module set was exposed outdoors with insulation on the back side in Arizona in the summer, and an identical set was exposed in environmental chambers. High precision creep measurements (+/- 20 um) and performance measurements indicate that despitemany of these polymeric materials being in the melt state during outdoor deployment, very little creep was seen because of their high viscosity, temperature heterogeneity across the modules, and the formation of chemical crosslinks in many of the encapsulants as they aged. In the case of the crystalline silicon modules, the physical restraint of the backsheet reduced the creep further.

14 SOLAR ENERGY↗
DOE OSTI2011

Ensuring Quality of PV Modules: Preprint

Photovoltaic (PV) customers need to have confidence in the PV modules they purchase. Currently, no test can quantify a module's lifetime with confidence, but stress tests are routinely used to differentiate PV product designs. We suggest that the industry would be strengthened by using the wisdom of the community to develop a single set of tests that will help customers quantify confidence in PVproducts. This paper evaluates the need for quality assurance (QA) standards and suggests a path for creating these. Two types of standards are needed: 1) QA of the module design and 2) QA of the manufacturing process.

14 SOLAR ENERGY↗
DOE OSTI2011

How Standards Control Module Design for Better or Worse (Presentation)

One would hope that PV modules are designed for survival in the outdoors. However, it appears that some module types are really designed to pass the qualification (IEC 61216/61646) and safety (IEC 61730 and UL 1703) tests. While this has resulted in an overall increase in module reliability and a reduction in infant mortality, it may not result in the most cost-effective solution for long-termreliability and minimum power degradation. This paper will provide several examples of module types and even solar cells designed to pass the tests that do not result in good cost-effective long-term solutions for outdoor performance. This presentation is meant to stimulate a discussion about how to remedy this situation and improve the overall PV industry.

14 SOLAR ENERGY↗
DOE OSTI2011

Opportunities and Challenges for Power Electronics in PV Modules (Presentation)

The presentation describes the value of adding DC converters and other power electronics to modules to improve their output even when shading or bad cells would otherwise decrease the module output. The presentation was part of a workshop sponsored by ARPA-E exploring the opportunities for power electronics to support PV applications.

14 SOLAR ENERGY↗
DOE OSTI2010

Module Technology: Current Practice and Issues (Presentation)

PV modules must provide mechanical support for the cells, protect the world from the voltages inside, protect the cells, diodes and interconnects from the weather outside, couple as much light as possible into the PV cells and minimize the temperature increase of the cells. The package must continue to serve these functions for at least 25 years as that is the typical module warranty period today. Furthermore the package must do all this for as low a cost as possible since the key to large scale PV growth is a reduction in cost while retaining excellent module reliability and durability. This paper will review current module construction practices for both crystalline silicon and thin film PV with emphasis on explaining why the present designs and materials have been selected. Possiblelong term issues with today's designs and materials will be discussed. Several proposed solutions to these issues will be presented, highlighting the research efforts that will be necessary in order to verify that they can cost effectively solve the identified issues.

14 SOLAR ENERGY↗