Not so long ago, quality of PV components and modules was the subject of concern mostly for those who built them. Today, buyers, insurers and investors all have a better technical understanding of solar product quality. Typical third-party “type approval” certifications merely ensure basic safety and qualification, and provide an entry point into the market. However, they have proved insufficient for the finance community. Investors want to know if a manufacturer can maintain quality in an everyday production process; if the current basic accelerated testing can be extended beyond the qualification testing to compare and differentiate the products from different manufacturers; if the commissioned power plants are susceptible to or undergoing durability and reliability issues; and how long modules will last in a certain climate.
To demonstrate quality of solar energy products and plants, a number of new evaluations and tests are being developed on the market.
At present, PV module manufacturers have their products tested only once to receive the type approval certifications. Testing random modules bought off the market or pulled off the power plant, not just the units provided by the manufacturer for testing, will provide an insight into the quality control at the manufacturing facility.
To ensure and demonstrate quality of solar energy products and plants, a number of new evaluations and tests are being developed on the market.
Current qualification tests probably have overlooked some of the failures and degradations that are seen in the field. The Qualification PLUS tests provide customers with additional information for choosing products that will last longer in the field. These tests are expected to increase confidence in the durability and reliability of PV modules.
Super combined comparative testing
This type of testing combines more than seven market-driven comparative testing protocols developed by various organizations with primary goals of low turnaround time, low price and low sample number. These protocols help manufacturers differentiating their products from others on the market and project developers evaluating module durability beyond Qualification PLUS tests. These tests are expected to increase confidence on the warranty provided by manufacturers and to help customers differentiate among various products.
Energy yield assessment
Comparing actual array energy yield of PV modules in multiple climates allows for a more comprehensive evaluation of their performance. Such evaluations help compare
- PV modules’ relative performance against competitors;
- Performance comparison of different PV module types in varying climates; and
- Actual performance versus various energy prediction models.
TÜV Rheinland PTL, PV Evolution Labs and Celestica recently launched a program inviting manufacturers to participate in such comparative energy yield program. Yield assessments can also be done for an entire PV power plant during a construction phase.
Independent energy production prediction
An investigation by Sandia National Laboratories in 2013 revealed a strong need for greater consistency of the energy production prediction models. The inconsistency exists between the users of the same model and between the models. Several industry-recognized models and software exist for the production prediction, including CEC’s 5-parameter, PVSyst, PVWatts, Clean Power, Maui, Retscreen and other models used in Europe. The project developers need well-trained personnel to evaluate these models for their specific application and site.
The project developers may choose an acceptance testing procedure that would allow them to make procurement decisions. Statistical acceptance testing through unannounced factory visits according to UL 4730 sampling procedure or other accepted procedure developed by the project partner can be used.
Ensuring installation and design quality of PV power plants helps enhance their bankability and increase cost-efficiency. These options include help in selecting suitable components and modules; testing module output performance to verify the output forecast and nameplate ratings as per various standards, including UL 4730, EN 50380, Sandia Performance Model and IEC 61853-1; site and plant design evaluations; and ensuring quality of the installation.
Yield assessments are done by solar testing providers as well as freelancers. However, there is no quality standard for installation inspections, energy yield assessments, soiling level investigation, module mismatch investigation, non-intrusive and non-destructive diode failure testing, energy production prediction and power plant inspections and evaluations. The industry needs a standard level of personnel training for those who offer these services.
Of course, additional tests come at additional cost, and there is currently no consensus on the best testing and sampling methods. One way to approach the dilemma is to statistically select the samples as per UL 4730 procedure or buy modules off the market after they have been type-approval certified and selectively test them. The tests do not need to be too expensive as they may eliminate the need to do multiple tests for multiple investors.
Written by Dr. Mani TamizhMani, President of TUV Rheinland PTL