Engineering topics
Publications and source records attributed to Otth, D. H..
Results are presented for a current set of accelerated long-term endurance tests on crystalline silicon module of various constructions. Cell materials include single crystal, semicrystal, EFG ribbon, and dendritic web ribbon. The latest data set is for the equivalent of 20-year life and showed satisfactory performance.
New materials were developed which show promise of fabricating modules that can pass the Underwriter Laboratories Class A burning brand test for fire ratable solar cell modules. It is concluded that fire resistant module design require special high temperature materials and constructions to achieve Class B and Class A ratings. Also, synergisms exist between back surface materials and module configuration.
The development of a qualification test for modules bypass diodes is reviewed. Diode junction temperature is measured, indirectly, under laboratory ambient conditions, and extrapolated to field conditions. Criteria are given for diode reliability.
Design criteria have been developed for bypass diodes in p-n and Schottky barrier in photovoltaic applications. A test method for assessing conformity to the design criteria is described. Junction temperatures are defined in terms of expected worst-case field conditions, including ambient temperature and solar irradiance on the photovoltaic module. The rating criteria address the maximum allowable current and heat-sink characteristics of diodes mounted inside or outside the photovoltaic module. The method establishes worst-case module-to-diode thermal interfaces and may be adapted for laboratory or field-site experiments. A list of the design criteria is given.
The evaluation of back-surface materials flammability in order to identify fire resistant module designs is examined. The fire test apparatus, burning-brand test sequence, and spread-of-flame test sequence are described. Video recordings and time-temperature profiles of module back surfaces are utilized to study the flammability failure mechanism and identify high-temperature materials. A table of flammability test results for various module designs is provided. The data reveals that 2-mil kapton, fiberglass cloth coated or impregnated with a material to plug pores, and metal foil back-surface materials achieve class A and B fire-resistance levels, and are applicable for photovoltaic module designs.
A series of photovoltaic module development activities, designated Blocks I through V, used increasingly refined requirements together with extensive testing and failure analysis to assist industry in developing the most advanced modules possible. The block program approach is described and the design details are given for all modules developed, highlighting the blockwise improvements. The success of this approach is demonstrated by the fact that most design details of the Block V modules have been adopted internationally. Instrumental to this success have been the steady improvements in design and test specifications that have guided module development. The experience gained since development of the Block-V specification is being incorporated into a Block VI Design and Test Specification, which includes upgraded and revised application-specific requirements. Highlights of this Block VI specification are also described.
A cooperative, cost-sharing research effort to develop a technology base required to construct fire-ratable photovoltaic modules has resulted in the identification of several high-temperature, back-surface candidate materials capable of raising the fire-resistance of modules using hydrocarbon encapsulants to Class A and B levels. Advanced experimental module configurations have been developed using back surfaces consisting of Kapton, Tedlar laminates, metal-foils, and fiberglass materials with high-temperature coatings. Test results (October 1984; March 1985; May 1985; and October 1985) indicate that several of these advanced module configurations are capable of achieving Class B fire-resistance levels, while a few configurations can achieve Class A levels. The paper summarizes activities to date, discussing flammability failure mechanisms, time-temperature profiles, and results of Block V environmental exposure tests of a candidate material suitable for both Class B and Class A fire-resistance levels.
Photovoltaic modules used in solar energy conversion are tested for flammability. Class B burning brand tests were conducted with the following results: module glass shattered and hydrocarbon encapsulants ignited. Penetration of back surface material was the prime cause of failure. Materials with greater flame and heat resistance are under consideration to increase back surface integrity up to Class A burning brand standard. The most promising is stainless steel foil.
A series of Class B burning-brand tests were performed on experimental modules using high-temperature, back-surface materials to develop the technology base required to construct fire-ratable modules. Results indicate the existence of synergistic relationships between hydrocarbon encapsulation materials and the experimental module configurations that provide increased fire resistance. These configurations use Kapton, fiberglass, neoprene rubber, stainless-steel foil or aluminum foil as the back surface. Successful test results occur when the structural integrity of the module back surface is maintained. Test failures of these modules always occur for one of three reasons: the outermost back cover melts, rips, or is too porous. In each case flammable molten encapsulant, its gaseous byproducts, or both, penetrates the back surface of the module and bursts into flame. Future efforts to complete the technology base will concentrate on the spread-of-flame test, focusing on the more promising configurations identified in the initial series of tests.
An assessment is made of results obtained by an experimental program having as its aim the identification of critical temperature-humidity bias degradation mechanisms in solar cell modules intended to have an operating lifetime of the order of 20-30 years. These mechanisms are studied in the context of conditions encountered over the course of long term operation in various sites in the U.S. Accelerated tests for the assessment of product lifetime entail the development of a correlation between test and application conditions; this has been accomplished through an analytical procedure for the correlation of time-varying field exposures to constant-stress accelerated environments.
The photovoltaic module failure mechanisms related to temperature, humidity, and electrical bias are analyzed using the data collected over a period of 20 years from various sites in the U.S. The approach is based on measuring the rate dependence of the mechanisms on site stress levels, and then using the rate data to analytically estimate the field life by means of computer models of the site environment. A correlation is established between the accelerated constant-stress testing and the time-varying field exposures. Test results are presented for two failure mechanisms for a module design featuring polyvinyl butyral encapsulant for the temperature range of 85 to 100 C and 85-percent relative humidity.
Viscoelastic shear dampers help eliminate microinch deflections resulting from low frequency vibrations. Dampers are applicable to control of tones and resonances in record players and turntables and other audio engineering equipment where vibration isolation is critical.
Design improvements and detailed functional analyses are reviewed to trace the development of a pyroactuated release device with segmented thread design from its intermediate design into one that reduces the levels of shock spectra generated during its operation by 50%. Comparisons of shock output and internal load distribution are presented, along with descriptions of mechanical operation for both designs. Results also show the potential areas where design development activity can gain further progress in lowering actuation shock levels.