Streamlining Due Diligence with the IECRE: Page 3 of 3
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Properly trained installers understand that it is important not to drop, twist or bend modules. Improper handling—such as carrying a module overhead with the weight resting on a hard hat—can crack PV cells and lead to hot spots. It is likewise important not to walk or kneel on modules during the installation process. Adjusting mounting hardware too loosely or too tightly can also damage modules. Since today’s modules often have thinner glass, thinner frames and larger collector areas compared to earlier products, they tend to have a lower tolerance for mishandling. System performance also suffers when installers connect mismatched modules or unequal string lengths to the same inverter or maximum power point tracker.
It is also important to monitor and track system performance to detect installation errors. Some errors, such as reverse polarity on PV source circuits, can dramatically reduce system performance right out of the gate. Other issues, such as scraped or punctured backsheets, only manifest with the passage of time. Recordkeeping and tracking not only allow for traceability but also provide a feedback mechanism that enhances learning. To the extent that you identify potential problems in advance, you can correct them at the project completion stage, before they have an adverse impact on performance and reliability.
The guidelines in the IEC 63049 technical standard also call for application-specific design adaptation. Consider a PV plant installed at a location that frequently experiences heavy snow loads or large hail, where the standard mechanical load tests, detailed in IEC 61215, may not provide a good indication of long-term reliability. In this scenario, you may want to use modules tested to enhanced mechanical loads and constructed with deeper frames or thicker glass, given the expected snow or hail loads. Designers could also opt for steeper or taller mounting systems where damage due to snow buildup and shedding is a concern. Similarly, quality designs can account for environmental conditions such as high wind loads, corrosion and extreme temperatures.
Test methodology is also an important consideration. Infrared (IR) thermography, for example, can enable rapid, economical detection of certain defects. With an appropriate temperature scale and resolution, IR testing has the potential to reveal a number of problems in fielded modules, including hot spots, bypass diode defects, solder bond failures, mechanically damaged cells and so forth. While aerial IR surveys may be most appropriate for some utility-scale PV plants, IR camera apps for cell phones may be adequate for surveying smaller systems.
Annual PV plant performance. A PV system energy test evaluates plant performance over time by comparing predicted and expected performance. Whereas predicted energy is based on historical weather data, expected energy is based on actual weather over the 1-year test period. These long-term energy test results provide valuable documentation regarding long-term PV system performance over the entire range of environmental conditions at a given site. (See “PV System Energy Performance Evaluations,” SolarPro, October/November 2014.)
To standardize performance evaluation activities, the IECRE includes an operational document, OD-402, regarding annual PV plant performance certification. This document defines terms—such as expected energy or energy performance index—that are essential for calculating plant performance. To facilitate feedback and learning, the test results are quantitative rather than merely pass or fail. The assessment accounts for nonoperational periods outside the control of plant operators, such as grid outages. It also compares actual O&M costs with the planned O&M costs and documents performance lost due to maintenance events. This feedback facilitates continual improvement.
Certifications in development. The list of operating documents in draft form or under development covers everything from project design to O&M.
Project design. A project design certificate, OD-403, is in draft form. This operational document will evaluate system designs against best practices for inverter and wire sizing, plant layout, shade analyses and climate- or region-specific considerations.
Project condition. A project condition certificate, OD-404, also in draft form, will address considerations related to asset transfer. This operational document will evaluate the repair and maintenance needs of fielded plants and use historical performance to estimate degradation rates and quantify risk and value. The project condition evaluation will also include a field survey to identify hot spots, browning, etching, corrosion, damaged interconnects, delamination and other issues that can impact performance and lifetime. This type of condition assessment could prove useful after an extreme weather event as a means of identifying weather-related damages.
O&M. A review is under way for an O&M certificate, OD-410, which will provide a quality management system for O&M companies. When complete, this operational document will certify that providers have the training and the tracking systems in place to comply with technical specifications such as IEC 63049 and IEC 62446-2, which covers grid-connected PV system maintenance. This certificate will address common maintenance issues such as vegetative shading between rows in PV farms. On sites where O&M providers need to mow weeds, they must avoid flinging rocks into module glass or backsheets in the process. Service providers need to protect against damage inflicted by people or animals as well. In addition, the O&M certificate will include standards related to cleaning and soiling. For example, a report in the IEEE Journal of Photovoltaics (vol. 6, issue 5, pp. 1,333–38) suggests that some methods of squeegee-cleaning operating arrays may permanently damage monolithic thin-film modules due to partial shading patterns. The new O&M operating document will ensure that cleaning methods do not damage modules. It will also provide guidelines for conducting cost-benefit analyses to optimize the timing of these activities.
Future opportunities. Other opportunities lie ahead to develop and implement additional certifications. In 2018, for example, the IEC expects to publish new standards for inverters and power conversion equipment that include guidelines for robust product designs and quality management systems. Once the IEC publishes this technical standard, IECRE working groups can develop an associated certification for inverters.
Status of Implementation
To date, 16 countries have joined the IECRE, including Austria, Canada, China, Denmark, Egypt, France, Germany, Hungary, India, Japan, Netherlands, South Korea, Spain, United Arab Emirates, United Kingdom and the US. These countries are the member bodies of the IECRE, each represented with a national committee. Rules of participation vary from country to country. In the US, the national committee members are organizations—companies, labs and agencies—that participate in renewable energy industries; each organization designates one or more individuals to represent it.
Numerous organizations have applied for authorization to participate in the IECRE, including certification bodies, inspection bodies and test labs. The IEC is in the process of approving more than two dozen applications. Some requests for proposals now ask for IECRE certification. Large-scale PV installations are likely to utilize the IECRE certification process first, with eventual adaptation at the individual consumer level.
—Katherine Jordan / Complex Review / Denver / complexreview.com
—George Kelly / American Renewable Energy Standards and Certification Association / Norwich, VT / aresca.us
—Sarah Kurtz / National Renewable Energy Laboratory / Golden, CO / nrel.gov