ECN publication
Levensduur van Solar Home Systemen : opzet en uitvoering van laboratoriumtests
Published by: Publication date:
ECN Energy in the Built Environment 1-6-2002
ECN report number: Document type:
ECN-C--02-007 ECN publication
Number of pages: Full text:
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In this work the reliability and lifetime of small domestic stand-alonePV-systems is studied. Previous monitoring studies have already showed that a large number of the installed solar home systems (SHS) and solar lanterns is not functioning properly. It is also known that low-quality products and incorrect sizing are important causes for this, yet little data is available on the operating conditions and the long-term performance of SHS. Especially the effect of the system configuration and operating conditions on battery degradation, which is systematically studied here, is not clear. Data from field monitoring and previous test results have been used to determine the principal factors that cause premature failure of lead-acid batteries. In order to analyse these factors a laboratory test has been performed in which 6 different SHS and 2 solar lanterns of the same type were operated under simulated field conditions. In the SHS three different automotive batteries and one type of deep-cycle battery were applied, in combination with three types of charge regulators. After the test all automotive batteries showed serious degradation, in contrast with the deep-cycle batteries. One of the automotive batteries broke down before the end of the test and two others broke down after the final capacity measurement. In all the cases a defect cell caused this. The number of cycles corresponds approximately to a practical use of 9 months for the SHS and 6 months for the solar lanterns. The battery that failed first was part of a SHS in which a relatively small battery was directly connected to the simulated module without the use of a charge regulator. During operation the charging efficiency was very low and the battery showed excessive water loss. The test results showed that in most cases a lower battery capacity due to ageing did not directly lead to reduced energy output. The common definition for the end-of-life, which is reached when the remaining capacity is less than 80% of the nominal value, is therefore not a proper estimate for the practical lifetime. Often a large battery capacity is chosen to obtain a good utilisation of the energy from the module and to prevent water loss and corrosion. However the test results show that a SHS with a smaller battery capacity combined with a constant voltage charge regulator is likely to perform well, as large batteries tend to be undercharged.

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