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
- 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:
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.
