ECN publication
Advanced reliability improvement of AC-modules (ARIA) : publishable report
Rooij, P.M.; Real, M.; Moschella, U.; Sample, T.; Kardolus, M.
Published by: Publication date:
ECN Solar Energy 1-9-2001
ECN report number: Document type:
ECN-C--01-093 ECN publication
Number of pages: Full text:
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The AC-module is a relatively new development in PV-system technology and offers significant advantages over conventional PV-systems with a central inverter : eg. increased modularity, ease of installation and freedom of system design. Countries like The Netherlands and Switzerland have a leading position in the field of AC-modules, both in terms of technology and of commercial, large scale, application. An obstacle towards large scale market introduction of AC-modules is that the reliability and operational lifetime of AC-modules and the integrated inverters in particular is not yet proven. Despite the advantages, no module-integrated inverter has yet achieved large scale introduction. The AC-modules will lower the barrier towards market penetration. But due to the great interest in the new AC-module technology there is the risk of introducing a not fully proven product. This may damage the image of PV-systems. To speed up the development and to improve the reliability, research institutes and PV-industry will address the aspects of reliability and operational lifetime of AC-modules.From field experiences we learn that in general the inverter is still the weakest point in PV-systems. The lifetime of inverters is an important factor on reliability. Some authors are indicating a lifetime of 1.5 years, whereas the field experiences in Germany and Switzerland have shown that for central inverter systems, an availability of 97% has been achieved in the last years. From this point of view it is highly desirable that the operational lifetime and reliability of PV-inverters and especially AC-modules is demonstrated/improved to make large scale use of PV a success. Module Integrated Inverters will most likely be used in modules in the power range between 100 and 300 Watt DC-power. These are modules with more than 100 cells in series, assuming that the module inverter will benefit from the higher voltage. Hot-spot is the phenomenon that can occur when one or more cells of a string are fully or partially shaded. Alpha Real has conducted considerable testing of shading and temperature rises of up to 180 C have been observed. Such a temperature rise will influence the lifetime and reliability of the module, and it is therefore common practice to protect modules from these conditions by using by-pass diodes. Having now an active element on the back of the module, such as a module integrated inverter, new possibilities are offered for new concepts for hot-spot prevention.

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