// Field tests of micro inverters

// Definition and implementation of field tests for photovoltaic module-level power electronics

Performance components at module-level, such as module optimisers or module inverters (micro inverters), are playing an increasingly important role on the photovoltaics (PV) market. They are specifically advertised as solutions for improving the yield of systems suffering from partial shading. Further arguments brought in their favour are increased system security via the option to switch off individual modules in the event of a fire, greater flexibility and various design options including simplified PV system design for installers, and availability and monitoring of module-level performance data for system operators. However, module-level power electronics are expected to be more reliable and have a longer useful lifetime than conventional string converters, i.e. comparable to that of PV modules – quite a challenge given the higher operational temperatures occurring on module level.

A test platform has been installed at ZSW’s Widderstall solar test facility to arrive at a near-realistic, time- and irradiation-resolved characterisation of the DC and AC performance of such commercial performance components, which allows for the testing of the respective module electronics (device under test, DUT) in direct comparison to a reference system involving string inverters. Various shading modes can be realised in this context, with DUT and reference systems always being subjected to identical shading conditions. In order to reduce system-related differences in the test arrangements and reduce the bias in the measurement components with the aim of improving measurement accuracy, both the DUT and reference measuring system and the PV modules may be alternated on an intermittent basis.