Convincing investors, insurers, and stakeholders that PV modules will last 25-35 years has become increasingly important, given the trend towards financial models that forecast 10 years of additional merchant revenue beyond the PPA. Now, more than ever, it is critical that the materials used in your module will be reliable for the duration of its operational service life. As service lifetime expectations of PV modules continue to grow, it is important that we understand the implications of durability on module performance and safety so that different stake holders can make informed decisions on materials selection.
Backsheets, in particular, play an important role in ensuring your module will be sufficiently durable to reach your financial objectives. While a module may pass standard qualification tests, backsheet defects can develop after just a few years of deployment in the field. The implications of poor backsheet selection involve not just significant safety risks, but considerable losses in performance and revenue.
Recently, a large IPP discovered one of their sites was producing less energy than predicted and started reviewing the system for failures. They found certain backsheets had started to crack and delaminate, leading to high leakage currents tripping inverters, and causing partial shutdowns and late starts. DuPont was invited to perform inspection of the affected PV field, using their Fielded Module Inspection Program. The team discovered widespread backsheet cracking and delamination on many of the modules. While the site was composed of modules from a single manufacturer and model, as many as three different backsheet types were identified, suggesting the module manufacturer used multiple Bill of Materials (BoMs) for the same project.
Modules buyers often have specific criteria for purchasing decisions, which may be restrictive to Tier 1 manufacturers, modules that pass PVEL PQP testing, or modules that are competitively priced. Little consideration is paid to what material is used to build the module. This approach is leading to some system wide failures due to catastrophic degradation of low cost materials that otherwise pass third party testing requirements. Consequently, IPPs are increasingly interested in customizing the BoM in modules during the RFP process. By specifying the components that are acceptable, IPPs can ensure that each manufacturer’s BoM is the same no matter which factory produces the module.
The PV industry offers very little information on module failures in the field. To assist buyers in understanding the breadth of component degradation issues that manifest in fielded modules, DuPont PVAM will soon be releasing its annual Field Survey This annual report is compiled from inspection and analysis of nearly 2 GW of PV installations by DuPont teams around the globe. Since 2011, DuPont has conducted inspections of 355 fields, and 130 module makers in Asia, North America, Europe, and the Middle East.
Often, fields are inspected at the request of system owners to help determine the causes of underperformance. The industry also lacks guidance on applicable remedies once failure has been documented. Most system owners rely on module warranties to address issues, but a deeper look reveals significantly greater impact on project economics. In a large field with widespread backsheet cracking, replacement costs of $120,000 per MW, exclusive of new module costs, have been estimated. This estimate does not include lost revenue or liquidated damages associated with non-delivery of energy under PPA contract.
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