Photovoltaic (PV)-converter-battery is the main part of a standalone building integrated photovoltaic system (BIPVS). Maximum power point tracking (MPPT) schemes cannot be applied to this section of a BIPVS because the output current of the PV panel is determined only by the state of charge (SOC) of the batteries bank which is the sole load of the PV panel in this section. In this study, a novel scheme is proposed to increase the energy efficiency of this section of a BIPVS. For the first time, it is shown that the energy efficiency of the PV-converter-battery section of a BIPVS is effectively increased by decomposing its PV panel into a set of parallel homogenous configured PV modules. Theoretical results obtained using the Lambert W function as a mathematical tool are presented that indicate parallel homogenous configured PV modules produce higher output power compared to all other configurations. Simulated results performed in MATLAB and PROTEUS environments are presented that explicitly validate the obtained theoretical results and verify an increase of about 10% in the energy efficiency of the PV-converter-battery section. Real experimental results are also presented that validate the simulation/theoretical results and verify an increase of 9.3% in the energy efficiency. (C) 2015 Elsevier BM. All rights reserved.