Standards for Photovoltaics

I recently returned from a week spent as one of the US representatives on the IEC Technical Committee 82 (TC82), which develops standards for solar photovoltaics. My focus is on Working Group 7, where we are working on standards including solar trackers and power and energy rating of concentrating photovoltaic modules. However, meeting with the rest of the TC82 community also gave me an opportunity to discuss issues in the design and testing of conventional wafer-based and thin-film modules.

While there are a number of groups working on standards applicable to solar (including the UL, ASTM, and NEC in the United States, CENELEC in Europe, and IEC and ISO internationally), the IEC plays an especially significant role because photovoltaics is a global market: major producers of polysilicon, cells, modules, and tools are spread across Europe, Asia, and the Americas, and customers are worldwide as well. Similarly, TC82 has members from 29 countries (including the major markets; China, Spain, Germany, the US, Japan, and France) working together to develop standards.

Standards are an important part of any growing industry.  For example, the SEMI International Standards Program is widely credited with speeding the growth of the semiconductor industry since the 1970s. Looking back, it’s hard to believe that at one point wafer sizes and shapes were not standard, and “custom-made solutions for each individual customer were the norm”[1].

For an industry whose value proposition depends on long product lifetimes in outdoor environments, standards that govern design qualification, accelerated testing, and safety of products are especially important. Additionally, standards for power rating, energy rating, and measurement are critical for allowing side-by-side comparison of different products.  This is especially apparent when trying to compare between crystalline PV, thin-film PV, and CPV.

Some of the PV standards we find most relevant in our work[2] are listed below. Where possible, I’ve also linked to free previews of the table of contents of each standard:

• IEC60904: Photovoltaic Devices
• This is a large, ten-part standard (IEC60904-1 is the numbering scheme for part 1, and so on) covering a number of device characterization areas such as measurement of I-V curves, spectral response, and solar simulators.

• IEC61215 (ed2.0, 2005): Crystalline silicon terrestrial photovoltaic (PV) modules: Design Qualification and Type Approval
• Note that a third edition is in development within the IEC.
• UL1703: Flat-Plate Photovoltaic Modules and Panels
• Note that this is also applied to thin film modules and in some cases in the past concentrating modules, though see also UL8703 below.
• IEC61646 (ed2.0, 2008): Thin-film terrestrial photovoltaic (PV) modules: Design Qualification and Type Approval
• IEC62108 (ed1.0, 2007): Concentrator photovoltaic (CPV) modules and assemblies: Design Qualification and Type Approval
• Note that for low concentration (<10x) modules, it is less clear whether they will be tested under IEC 62108 or an adapted form of IEC 61215. And some concentrating systems such as heliostats differ from the main focus (no pun intended…) of IEC 62108.
• On the IEC committee we are actively soliciting feedback on the first edition, as we work on a second edition.
• UL8703: Concentrator Photovoltaic Modules and Assemblies
• UL1741 and the just-published European standard EN50530 cover inverters
• The PV Resources web site contains a more exhaustive list of standards, though it is somewhat out of date and does not mention some of the newest standards. And the standards above cover a significant portion of what companies we work for care about.
• You may also find this UL diagram of UL/IEC PV standards by system component informative.

For anyone who was new to the industry, I hope this list of information is useful. 

That said, qualification standards only outline the bare minimum testing. It’s important to design tests to simulate other failure modes and environmental conditions not included in the standards. In addition, testing identifies certain failure modes that are more systematic (damp heat for the previous generation of thin-film modules, for example), helping guide areas for design.  Including testing early in the development path is important: we have seen some companies develop a first prototype, only to require major design revisions once they begin thinking about reliability, DFM, and qualification. 

The topic of PV module design for reliability could be a whole separate discussion, but two documents to get you started down this path are:

• NREL's "non-comprehensive summary of the most common types of failures for each PV technology", with 53 references to additional papers
• Another paper out of NREL, published in 2009: "History of Accelerated and Qualification Testing of Terrestrial Photovoltaic Modules: A Literature Review"

Standards themselves don’t necessarily inspire passion and dedication in everyone, but their purpose overlaps with the desire to design and build high-quality, reliable, cost-effective technologies that can solve some of our pressing energy supply and environmental issues. And doing that makes us at GreenMountain very excited. Come back to this blog next week for a post about the scalability of solar, examined from a variety of perspectives (land usage, capital requirements, labor, and growth rate). 

[1] The SEMI International Standards Program – History, Successes and Lessons Learned to Address Compound Semiconductor Manufacturing Challenges, http://www.csmantech.org/Digests/2006/2006%20Digests/4A.pdf

[2] I'm putting the "about us" blurb down here in a footnote as many readers may already be familiar with us: We offer design engineering for hire, including engineering of products, automated tools, and software for many companies in the cleantech sector. This includes extensive experience in the solar industry (we’ve done design engineering for dozens of solar companies). The product-related standards I mention in this post are less relevant when we develop manufacturing tools, but do come into play when we design solar modules, encapsulation, interconnects, CPV receivers, or a range of other solar components.