A PV module being subjected to hail testing at Fraunhofer ISE.
Financing photovoltaic power plants can be an uphill battle. As with any power plant, the payback time to recover the upfront building costs is a crucial factor in securing project funding. With a PV project, uncertainty around PV modules’ long-term durability in their operating environment increases the perceived risk. As solar modules age and degrade, their power output decreases, gradually making the PV power plant less productive. To account for this, finance models need to be able to predict how long a module will remain operational and at what rate the power output will decline.
The current International Electrotechnical Commission (IEC) testing standards used by the solar industry focus on assessing manufacturing quality and “infant mortality” in the field; they don’t yet provide sufficient information to assess the lifetime durability of solar modules or their long-term degradation rates.
Current tests also lack protocols for comparing the relative reliability risk among different module designs. Without these benchmarks, financial models must instead depend on a patchwork of methods for creating predictions for relative durability, making it difficult to quantify which solar modules are best suited for a particular installation. That uncertainty creates confusion that increases perceived risk, delays financing, and ultimately raises the cost of building PV power plants.
Over the course of their operational lifetime, modules experience shifts in both cause and frequency of failures – a trend captured in the “Bathtub Curve”. Click for a larger image.
Fraunhofer, with its decades of experience in the development, testing, and qualification of solar technology, has teamed up with PV module developers, manufacturers, and financiers to create a more comprehensive testing protocol for assessing PV module durability – the Photovoltaic Durability Initiative (PVDI).
First announced in 2011, PVDI is a joint venture between the Fraunhofer Center for Sustainable Energy Systems (CSE) and its German sister institute, the Fraunhofer Institute for Solar Energy Systems (ISE), that aims to create a durability assessment protocol which will eventually form the basis for an international industry standard. The first round of PVDI modules has been tested under the new protocol; the results will be presented at next week’s PV Rollout Conference in Atlanta, Georgia, while a more in-depth discussion of data and testing procedures will be published in the weeks ahead.
At the core of the PVDI are accelerated test protocols that extend beyond the existing IEC tests for module performance and safety. PVDI’s accelerated stress tests range from mimicking wind stress via low-temperature dynamic loading to simulating hot, dry climates by exposing PV modules to high temperatures and ultraviolet radiation.
The tests also include more typical stresses such as temperature cycling, humidity-freeze, and damp heat exposure. The result is a quantitative, third-party analysis that addresses investors’ durability concerns. PVDI promotes further industry development, provides a comparative ranking of PV modules, and makes detailed data available to the participants.
The current PVDI testing protocol. Click for a larger view.
PV modules may be submitted to PVDI testing by module manufacturers, project developers, and other stakeholders in the PV industry who are interested in a comprehensive picture of module performance and reliability. Going beyond simple pass/fail ratings, a quantitative scoring system provides a way to rank modules based on their durability.
And in order to encourage widespread participation in the program, confidentiality is strictly protected. The manufacturers of modules tested in the program have the option of withholding their identity from published reports thereby benefiting from knowing how their products stand up to the competition without the risk of exposing themselves to bad publicity.
Top performers, however, have the added incentive of attaching their name to their results and making consumers and financiers aware of their products’ superior quality. Though participants have the option to remain anonymous, the data generated – without identification – remains part of the PVDI dataset for comparison with the rest of the field. The public reports will therefore provide a window into the distribution in quality of commercial modules available in the marketplace.
Long-term outdoor testing in a variety of climate zones supplements laboratory testing and helps verify the protocol as a whole.
From its inception, PVDI has been constructed as an evolving standard. Over the course of the program, Fraunhofer CSE and ISE will continuously validate and refine the test methodology. In parallel with the accelerated tests, modules will be subjected to long-term outdoor exposure, making it possible to examine the correlation between accelerated lab tests and actual operation in the field. PVDI workshops will be held yearly, allowing program partners to discuss findings and suggest improvements to the protocol.
By determining the appropriate metrics and establishing strict standards for PV durability, Fraunhofer hopes to reduce the risks – and costs – involved with PV investment, making it easier for PV companies to secure the funding needed to advance production and installations. By making detailed reliability data available to PV stakeholders and creating venues for collaboration, Fraunhofer is optimistic that the new PVDI program will ultimately accelerate deployment of PV throughout the world.
Fraunhofer is currently recruiting new participants for the next round of PVDI testing. Manufacturers, utilities, and investors who are interested in submitting modules for evaluation are encouraged to contact Geoffrey Kinsey, CSE’s Director of PV Technology, at [email protected].
