As PV solar power is becoming the most important renewable energy resource, more and more users have concerns for PV systems. Here addressed outlines the reliability issues of modules, the core of PV systems.
When we talk about PV technology, it means mainly the technology of solar cells in the PV modules. Since two decades ago, the technologies of solar cells have been focused on the improvement of energy conversion efficiency, which experienced stages from BSF (backside-field), PERC (Passivated Emitter and Rear Cell), TOPCon (Tunnel Oxide Passivated Contact), and HJT (Heterojunction Solar Cell) to the most advanced BC (back-contact cells) today with conversion efficiency of solar cells increased from around 15% to over 26%. Accordingly, the powers of PV modules have progressed as well. Therefore, the powers or conversion efficiency of PV modules are mainly determined by the solar cell technologies, while, on the other hand, the reliability PV modules is decided by the module technologies.
In general, the key manufacturing processing of PV modules consists of two aspects: the connection between cells in series electrically and the lamination of layered materials, as shown in the figure below.
For the layered materials, there is no much difference for different manufacturers. However, the approach of inter-connection between cells is rather critical as it affects the performance and reliability of the modules significantly. The connection approach differentiates the technology of modules.
Conventionally, the inter-connection between cells is realized by using ribbons (copper stripes coated with soldering tin) to connect the front electrodes of a cell to the backside ones of its neighboring cell (see figure a below) or to connect the electrodes at the backside of a cell to the ones at the backside of its neighboring cell (see figure b or c).
As well known, however, the inter-connection with ribbons exists intrinsic disadvantages, such as stress and heavy metal typically. The stress at the edges due to the bended ribbons and the stress on the cell surfaces due to soldering could cause micro-cracks, which have been identified as the major factors responsible to the power degradation and reliability of PV modules. At the same time, the soldering materials coated on copper stripes for ribbons contain heavy metal (Pb), which has become the significant issue today due to recycling concern.
In fact, there have been a lot of efforts to solve the problems of stress and heavy metal Pb. Thanks to the creative idea of planar electrical connection (PEC) technology, which replaces the ribbon connection approach by using patterned planar-conductive-foils combined with an punched insulating encapsulate composite (IEC), as shown in the figure below. The innovated connection mechanism for the inter-connection of cells roots out the problems of conventional ribbon connection approach.
In conclusion, the performance of PV modules is decided by both the solar cell technology and modules technology. The module technology itself plays an even more important role on the reliability of PV modules. The PEC technology, obviously, makes the PV modules significantly unique, especially in high efficiency, harmful heavy-metal free and better reliability for longer lifetime. With example as below, the main technologies used in different modules can be identified easily.
It is believed that, as the most advanced technology, planar electrical connection (PEC) is becoming the dominant and unique technology to manufacture high reliable PV modules, including especially lightweight modules, flexible modules, PV roof-tiles.
