MANUFACTURINGOUTLOOK
Figure 4: (a) imec’s i-module process flow for back-contacted solar cells and (b) View of a ‘mini’ -i- module of 4 back- contact solar cells with a thickness of 120µm
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understanding of the physical and chemical degradation processes (and in particular their acceleration factors), exhaustive accelerated lifetime tests, and finite-element modeling (based on accurately measured material properties).
The future PV landscape Today, the operational lifetime of PV modules is typically about 20 years. In the future, the added functionality in combination with intelligent control strategies, and the evolution towards module integration technologies could positively affect their lifetime. However, if we want to boost this to 30 or even 40 years power guarantee, we will also need new test methodologies for module lifetime prediction. Today, module lifetime guarantees provided by industry are essentially based on past field experience on the one hand, and on passing specific qualification tests as a means to compare between products on the other hand.
Strictly speaking, these tests do not provide failure rates. In order to perform cheaper and quicker lifetime assessment, we need ageing models that can predict failure rates. They need to be based on an exhaustive knowledge of all failure modes (gathered from outdoor testing), a fundamental
Of course, these models need always to be validated with outdoor tests, under various climates and conditions. This extended R&D activity will require an industry-wide collaboration effort but may have a determining impact on the economics of the PV sector in view of the potential cost savings related to longer lifetimes. Reversely, detailed models of failure modes and in particular their dependancy on specific local operating conditions could one day allow the manufacturing of ’just-reliable-enough’ modules – modules that are designed to counter the prevailing failure modes encountered in a given operational site – but without material upgrades and design features that are adressing non-prevailing faillure-modes.
Also, the optimal choice of the ‘smart’ components to add will depend on a variety of factors, such as the site location, the monthly average light intensity, the estimate losses due to shade, snow and dirt, etc. In addition, the exact ‘looks’ of a module will differ according to the market segment. We believe that elements of smartness will first be introduced in residential systems, where less ideal illumination conditions are mostly to occur, and where the user is often willing to pay a premium to improve or maintain efficiency. Later
www.solar-pv-management.com Issue IV 2011
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