The self-deception is the base of “the Emperor’s New Clothes” story.
Sometimes it is difficult to realize that something is not real. It requires that someone comes up with something new to help us to see the reality.
Yes, maybe it is the time for the PV people to realize and see that the "King-module" is naked, from the PID perspective.
How Encapsulants Can Avoid Voltage Losses (PID defect and others) in PV Modules?
Gains and Looses in PV Modules: Starting at 18,66% Cell Yield to End Up at 16,05%
There are several factors that can affect the performance of crystalline photovoltaic modules. The main sources of influence have been analyzed and studied at the Fraunhofer ISE (Ref: From Cell to Module efficiency, I. Häidrich H. Wirth, M. Storz, G. Klingebiel, Fraunhofer ISE, Schmidt 2012) and summarized later by Gabor Photovoltaics Consulting LLC at the Intersolar July 2013. In general, all of them can be grouped in just three main grouped factors:
- Module format factors Including inactive areas
- Electrical factors. Losses generated by string formation and cables mainly
- Optical factors. Losses and gains generated by the various interactions between cell, Encapsulant, glass and backsheet
Another, and important, Electrical Loss: the PID
In addition to the previous list of described factors, there is also another one, which can seriously damage the modules performance and their reliability in extreme. Module’s voltage stress can seriously affect their operation yields, especially if module elements are not well suited to manage these stresses. This factor can be grouped inside the Electrical group of factors, being a really important one. Some researchers have decided to name it as Potential Induced Degradation (PID) effect. This type of electrical defect can move away modules from their regular window of operation and have a massive impact on module reliability (Ref: P. Hacke et a., Testing and Analysis for lifetime Prediction of Crystalline Silicon Modules Undergoing Degradation by System Voltage Stress. 38th IEEE PVSEC, Austin 2012). At the first stages of the PID phenomena, the power losses are small and take place spontaneously, but they can become a constant loss and rise up over time reaching values of 5% electrical losses, or even more, reaching until 30%, with disastrous damage to the modules.
But this type of electrical loss is not just limited to crystalline technologies it also happens on Thin Film technology modules. According to the latest research, PID is caused by the diffusion of positive sodium ions and water vapor penetration into the boundary between the glass and the transparent conductive oxide on the front of the thin film cell.
The causes of PID
To understand the causes of this type of electrical losses either in Crystalline or Thin Film technologies, several Photovoltaic Institutes (Fraunhofer IS, PI Berlin, NREL, CENER, et al.) have been working since 2010 on the issue. Their works and conclusions have been presented in several PV Conferences and published in Scientific papers. In parallel we, at NovoGenio, also initiated several internal projects to develop new PV Encapsulants to minimize and avoid such a defective electrical discharge and modules potential losses. We should not forget that the Encapsulants, being the joint material between all the parts, are the media that facilitate or avoid the electrical conductivity and consequently the electrical leakages inside the modules.
In general all studies have concluded that electrical losses due to Voltage Stress are mainly dependent of modules conditions like: systems voltage, humidity, temperature, and contact situation. Any of them “playing alone” or “playing with others” at the same time can seriously damage the modules performance and life.
The Remedies for PID
To avoid them, the module makers have the high responsibility to review the design and specifications of all module parts and the way they will have to be integrated to get the best of all. Only by being conscious of the long lasting guaranteed reliable life that a module should offer to the Market, it will be possible to choose raw materials in a cost-effective manner.
Trying to support and help, several parts companies have seriously come up with upgraded and more developed materials to enhance modules yields and reliability. Going in that direction some cell manufacturers have developed new surface cell treatments to avoid electrical charges accumulation and consequently the unwanted electrical leaks. In the same way, some glass companies have developed special glass compositions reducing the quantity of Na+ and replacing them by K+.
At NovoGenio, we want to be a reliable part of that process as well, by supplying Quality Certified Technical Films to support module makers to achieve the higher standards in Market. We have worked out some new type of Encapsulants with higher dielectric properties over the standard EVA ones. To know about how Encapsulants contribute to Electrical Losses and to help you select the best material to construct your modules you can download the following Document:
The Dielectrical Properties of Photovoltaic Encapsulants: Measurements and Values.
In this Document, of 12 pages long, you will find clarifying information about:
- The key Roles that all Encapsulants in photovoltaic Modules should meet.
- The Conductive and Dielectric properties of materials
- The Electrical Insulators available to construct Photovolaic Modules
- The Dielectric Limits of the Encapsulators’ King today, the EVA.
- How to Measure and Control the dielectric Limits of Encapsulants
- The Possible Adjustments that can be done in EVA Encapsulators to improve their isolation levels
- How to Overcome the Limits of EVA for sure: “The Dress of the King”
Hopefully this information will help you to see that the " King-module" is naked from the point of view of the PID. And at the same way the reading will help you to dress the King.