PV Modules

Double-glass PV modules are emerging as a technology which can deliver excellent performance and excellent durability at a competitive cost. In this paper a glass–glass module technology that uses liquid silicone encapsulation is described. The combination of the glass–glass structure and silicone is shown to lead to exceptional durability. The concept enables safe module operation at a system voltage of 1,500V, as well as innovative, low-cost module mounting through pad bonding.

We are always hearing about champion cells demonstrating efficiencies of 24% or higher, yet only 20 or 21% can be obtained at the module level. This paper highlights the different loss mechanisms in a module, and how they can be quantified. Once it is known where photons and electrons are lost, it is possible to develop strategies to avoid this happening.

The backsheet is the first barrier for ensuring the reliability and durability of PV modules for 25+ years. To reduce cost, backsheets with a variety of compositions and constructions have been developed and introduced in PV modules. For PV module manufacturers, a major challenge is choosing a low-cost backsheet that can maintain the current levels of high reliability and durability performance. In the work reported in this paper, the properties of several backsheets of various compositions and constructions were compared.

This paper demonstrates that the future of the lowest-cost electricity generation from PV is not all about increasing cell and module efficiencies and minimizing cost/Wp, but rather squeezing the best out of a system using a few simple tricks, such as bifaciality, tracking and ground reflection improvements, to achieve the lowest cost/kWh.

Newly developed high UV light transmission ethylene vinyl acetate (EVA) has recently been extensively introduced for use in PV modules. It has been proved that this type of EVA can result in potential power gain because of the better blue light response of the solar cell, which in turn can further reduce the cost per watt of the PV module. However, if only high UV transmission EVA is used as an encapsulant, too much UV light irradiates the backsheet, which can cause the backsheet to yellow. In order to improve the reliability and durability of the modules, SUNTECH, as a module manufacturer, therefore uses combined EVA, i.e. high UV transmission EVA as the front encapsulant and conventional UV cut-off EVA as the rear encapsulant, to protect the UV-sensitive backsheet. This paper presents the results of an investigation of the reliability and durability of high UV transmission EVA in PV modules, through an enhanced UV test which exceeds IEC standards.

One of the main concerns of module manufacturers is the power loss that takes place when the solar cells are incorporated in PV modules. This power loss, known as cell-to-module (CTM) loss, results from the influence of many factors which occur during module production. Some of these factors lead to a gain in power at the end of the process; on the other hand, some are responsible for a loss of power and offset the positive effects of other ones, resulting in a net power loss. In this paper the CTM losses will be addressed from an industrial point of view and for standard crystalline PV modules. The focus will first be on some of the most frequent issues detected in production lines and their influence on module power loss. More extensive research is then carried out to arrive at an explanation of their origin. This paper describes some of the mentioned factors along with the different ways of detecting them.

Poor insulation resistance in modules is one of the primary contributors to module failure. Regimes currently in place to test the insulation resistance of crystalline silicon modules have proved problematic, as the conditions found in a laboratory are not on a par with environmental conditions at installation sites. This paper explores the shortcomings of current testing standards and recommends further tests that should be introduced to prevent module failures in the field.

High-efficiency (HE) PV technologies, such as heterojunction, back-contact or n-type, can be affected by significant measurement errors compared with conventional technologies; the power measurement of HE crystalline silicon PV modules and cells has therefore been a challenge for the PV industry for at least two decades. To deal with the internal capacitance and the spectral mismatch errors of HE cells and modules, various measurement techniques are currently used: steady-state, multi-flash, dynamic I–V, DragonBack™ and dark I–V and reconstruction methods, to name a few. This paper discusses the challenges and provides guidance for best practice for acquiring accurate measurements.

Potential-induced degradation (PID) of the shunting type (PID-s) is one of the most severe forms of PID, which is caused by the negative potential of p-type solar cells with respect to grounded frames/mounting. Although this negative potential can be completely avoided at the system level, that is not the case for a large number of modern PV systems. PV modules that are able to sustain PID-s stress for at least the duration of their service life are therefore essential. To assess whether modules fulfil this requirement, laboratory tests are currently recommended in which the modules are exposed to a certain constant level of PID-s stress for a given amount of time. These types of test with constant stress levels, however, are only feasible in the case of degradation mechanisms that are not reversible in the field, for which non-coherent stress episodes simply sum up to the total stress. Unlike other mechanisms, PID-s is reversible under field conditions; as a consequence, the level of PID-s of a fielded module is the result of an intricate interplay of phases of degradation and regeneration. This behaviour cannot be replicated in a laboratory test using a constant stress level; the currently recommended laboratory tests for PID-s with constant stress levels are therefore not appropriate for assessing the service life duration, and can only be used for differentiating the susceptibility to PID-s stress and for monitoring the stability of production processes. For monitoring the PID-s resistance of its products, Hanwha Q CELLS uses tests for PID-s with constant stress in accordance with the draft for IEC PID test method 62804. This assures that all the products of the Q CELLS brand come with Anti-PID Technology (APT). The expected service life duration with respect to PID-s is assessed by simulating the interplay of degradation and regeneration under non-constant outdoor conditions that are based on meteorological data.

In the last few years PV technology has seen continuous improvements, with significant enhancements at the cell and module levels. In addition to the requirement of high efficiency, the long-term reliability of PV modules leads to proposals for innovative module concepts and designs. Meyer Burger has developed a low-temperature wire-bonding technology, known as SmartWire Connection Technology (SWCT), with the aim of offering a cost-effective solution for high-efficiency solar cells while minimizing cell-to-module losses. The introduction of this interconnection design immediately brings new challenges, especially in the selection of an appropriate encapsulant, which must ensure a good processability as well as the required long-term module reliability. The compatibility of the most cost-effective types of encapsulant currently available on the market was analysed in the study reported in this paper. Thermoplastic polyolefin encapsulants with water absorption less than 0.1% and no (or few) cross-linking additives have proved to be the best option for long-lasting PV modules in a glass-glass (GG) configuration. The development of a laminator having a symmetrical structure (two heating plates without any vacuum membrane) has also opened the door to fast lamination processes with cycle times under eight minutes.