Technical Papers

Extended crystal defects, such as grain boundaries and dislocations, have long been considered the main factors limiting the performance of multicrystalline (mc-Si) silicon solar cells. However, because the detrimental effects of these crystal defects are reduced as a result of improvements in the solidification process as well as in the feedstock and crucible quality, the degradation caused by boron–oxygen complexes is expected to be of increasing importance. Light-induced degradation (LID) occurs in both p- and n-type crystalline silicon solar cells that contain both boron and oxygen. Because of the fundamental differences in the solidification processes, mc-Si silicon contains less oxygen than Czochralski silicon; nevertheless, the oxygen content in mc-Si silicon is still sufficient to cause degradation, although to a lesser extent than in the case of Czochralski silicon. Whereas B–O-related degradation of 0.5 to 1% abs. can be found in Czochralski cells, the degradation in conventional mc-Si cells is limited to around 0.1 to 0.2% abs.

The market outlook for utility-scale PV installations is very positive. These PV plants have the capability of supporting grid operation, and the ability to do this is being increasingly required in grid codes. Testing the capabilities of very large PV inverters, however, is demanding for laboratories. Gunter Arnold, Diana Craciun, Wolfram Heckmann and Nils Schäfer from Fraunhofer IWES discuss current developments and resulting challenges and address the gaps and diversity in testing guidelines and standardisation.

As early as 2010, Phoenix Solar along with Saudi Aramco installed the first of three PV test facilities in Dhahran, Saudi Arabia, putting four different module technologies (monocrystalline, amorphous-microcrystalline, CdTe and CIS) to the test in extreme climatic conditions. Klaus Friedl of Phoenix Solar LLC shares some hints and lessons learned from the tests.

Maximising production from a PV system is critical, since nearly all of the investment is made prior to system activation. Monitoring of PV systems allows operators to identify any performance or safety problems early so that they can be repaired quickly, thus minimising energy losses. Joshua Stein of Sandia National Laboratories and Mike Green of M.G. Lightning Electrical Engineering discuss some new monitoring strategies that are necessary for expeditiously identifying and locating system faults.

New inverter technologies offer installers the choice of central of distributed systems for PV arrays. Deciding which system is the most optimal to use isn’t always based on the size of a solar system, writes Alvaro Zanon.

More than ever, the global PV market provides attractive new investment opportunities, but the elements driving such rapid expansion also increase the risk of solar financial assets failing to meet long-term fiscal and performance goals. Boris Farnung, Björn Müller and Klaus Kiefer of Fraunhofer ISE, and Peter Bostock and John Sedgwick of VDE Americas explore major quality-assurance measures and the challenges today for achieving bankability of utility-scale PV plants.

A significant part of the risk management process associated with large-scale solar PV installations is ‘technical due diligence’, which seeks to define and minimise all technical risks associated with the project. Fred Martin and Nick Morley of TÜV Rheinland explore due diligence challenges for PV power plants in Japan.

Sophia, a four-year European Commission-funded project to promote coordination across the EU's PV research community came to an end in January. With 20 partners drawn from industry and academia, the project appears to have fulfilled its aims of fostering greater collaboration. But with Europe's PV manufacturing industry facing a dire predicament in the face of competition from Asia, is it too little, too late?

The current standards (IEC 61646 and IEC 61730-2, and IEC 62804 draft for c-Si only) are clearly insufficient to guarantee satisfactory long-term stability and energy yield for thin-film modules, given that reports from the field, as well as from laboratory test results (beyond IEC testing), in some cases show significant degradation of IEC-certified modules. Accordingly, thin-film modules can also exhibit degradation effects, such as TCO corrosion and power degradation, because of potential-induced degradation (PID). This paper presents the results obtained for thin-film modules subjected to bias and damp-heat (BDH) conditions in both indoor and outdoor tests. In order to assess module lifetimes for different thin-film technologies with respect to PID, indoor- and outdoor-determined leakage currents are compared and analysed, taking into account weather data and results from accelerated ageing tests. Finally, on the basis of simulations and investigations for different installation locations, module lifetimes are estimated and discussed.

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.