Photovoltaic connector behaviour under accelerated fretting testing regimes

Photovoltaic modules have no moving parts and last upwards of 25 years with no maintenance aside from occasional cleaning. The installation of modules in building facades and other structures has necessitated the use of push fit connectors to enable quick and easy inter-module DC electrical connection. New applications for photovoltaics such as roof shingles (tiles) place further performance demands on connectors. The day-night variation in temperature within a PV roof for example, creates component expansion. This paper details the behaviour of a tin plated copper photovoltaic connector under small amplitude fretting tests (10-100 μm) using a specially developed accelerated lifetime test rig. The mated connector creates a high force, multiple point contact between the male and female components by the use of a prestressed spring collar. The study shows that a transition amplitude exists (~13 μm) above which gross slip at the connector interface appears to occur. This causes a gradual linear increase in contact resistance, followed by a sudden change to rapid wearing of the tin plating on both the connector surfaces and spring collar, leading to connector failure. Below the transition amplitude, partial slip at the connector interface is observed which creates a stable, low contact resistance. The paper highlights the need to maintain a partial slip/stick condition within a PV connector for long term contact resistance stability. The implication of this requirement for photovoltaic connector design and application is discussed, considering the benefits of flexible connector housings and lubricants in particular