Survey Reveals PV Test Priorities and Practices
Solar cell manufacturers recognize the need for complicated tests, but do not seem too worried about being able to integrate them in their production lines if they help to increase efficiency, according to a survey done by Keithley Instruments.
Alexander E. Braun, Senior Editor -- PV Society, 1/28/2010
A survey of solar cell/photovoltaic (PV) device researchers and manufacturers working in government, university and corporate labs, and manufacturing facilities indicates distinct differences in testing methods and priorities among respondents from Asia, North America and Europe. Keithley Instruments Inc. (Cleveland) conducted the study during the summer of 2009 using a by-invitation-only online survey generating 564 responses.
Overall, the survey showed the industry is focused on improving device efficiencies as its dominant development priority. Manufacturing costs reduction was the second most important among the respondents, although substantially less significant than the need to boost device and panel performance.
Parameters characterized as part of R&D as reported by respondents located around the world and in Asia. (Source: Keithley Instruments)
A large majority of respondents engaged in solar cell R&D worldwide identified their measurement key parameters as short-circuit current (ISC), open-circuit voltage (VOC), maximum output power (PMAX) and, to a lesser extent, conversion efficiency. North American and European respondents showed consistent agreement on what constitutes their most important tests, with a well-defined gap between these top four and 10 other tests. Asian respondents, while agreeing with the same top four tests, showed considerable less preference for them, while other tests were cited as key parameters nearly as often as the top four.
The top three tests indicated by respondents are consistent with what the company's customers describe as their important methodologies in the research phase, according to Mark Cejer, Keithley's marketing director. "We were a bit surprised not to see more priority given to shunt resistance and series resistance tests, as we hear quite a bit about how important those measurements are to characterizing device performance," he said. "Overall, other than a clear preference for the top three tests, there remains a significant amount of variation in the industry about what tests are most meaningful. There may be several reasons for this variation. For example, the tests used may vary depending on the cell technology or on the market for which they are intended. Also, many of the solar cell technologies are relatively new and therefore there are no industry-standard testing methodologies."
The priority of test parameters characterized as PV moves into production remained much the same, but there was far less agreement about the most important tests than what is found in the research lab. Asian respondents were more definitive about the most valuable solar cell tests for production, rather than for research.
Generally, engineers seem relatively unfazed by the solar cell industry's complicated battery of tests. When asked which tests presented technical challenges, none of the 15 tests appeared to pose a problem for a large portion of the respondents, either in the research or production test phase. This held true for even the most demanding tests on the list, such as quantum efficiency and conversion efficiency. Maximum power output was identified as the most difficult test to perform, with 28% noting it as the "most challenging," perhaps reflecting the difficulty of integrating 50 W power supplies into a test system for this type of research.
Respondents reported engagement in a broad range of solar cell/PV device technologies, including established, relatively well-characterized technologies for making PV devices out of monocrystalline, multicrystalline or amorphous silicon, as well as newer thin-film technologies such as CIGS, CdTe and GaAs. In general, respondents seemed more active in thin-film materials than in silicon, perhaps due to the improved response rates and capacitive properties of thin-film materials.
Given the staggering array of device technologies now being explored or developed, the industry seems poised to become larger and increasingly competitive, with manufacturers making significant investments in finding new ways to extract the maximum energy at the lowest possible cost from every photon that reaches their products. Asian manufacturers appear firmly committed to playing a major role in the worldwide solar cell industry.
The white paper, "Keithley Instruments' Solar Cell Test Survey," summarizes the results and is available for downloading from Keithley's website.
