Module-level direct coupling in PV-battery power unit under realistic irradiance and load

A photovoltaic (PV) module, battery and consumer or load is usually tied together by a complex power electronics, including maximum power point tracking (MPPT) device for power coupling to maximize output of the PV modules. At the same time, a typical battery itself can play the role of a power coupling element in addition to its main energy storage function. In principle, a properly chosen PV-battery pair can maintain a high degree of internal power coupling even under variable irradiance and load without MPPT electronics. This option is of interest for e.g. module-level integration of PV and battery to cope with natural intermittency of a PV module power output. In this work, we experimentally examine the function of a laboratory scale unit of a 7-cell silicon heterojunction PV module directly connected to a lithium-ion battery and variable load. The unit is the simplest PV-battery module representative for detailed study under a series of emulated realistic profiles of irradiance and power consumption. The directly coupled PV-battery unit shows coupling efficiencies of above 99.8% at high irradiance and approx. 98% on average through the daily cycle – a value that is comparable to modern MPPT device