In this study we examine the solar radiation conversion into thermal energy and energy storage into phase change material (PCM) in the photovoltaic thermal (PVT) collector system. In order to get better solar radiation satisfactory compound parabolic concentrator (CPC) has been mounted on PVT collector. In this study outdoor experiments were carried out to compare performance study between clear day and semi-cloudy day in winter season. PVT solar collector with CPC that act as a solar collector, a PCM tank and CPC was integrated into one piece because of simplicity structure for PCM storage in same unit. No connection pipe i,e small area needed for installation and continuous tracking was not needed for better concentration ratio. Total heat loss, total useful energy, thermal efficiency and overall efficiency of the collector by varying different parameters were evaluated using modified equations derived for the energy storage system from the basic derivation of Hottel-Bliss-Whillier. The results show that thermal efficiency of solar collector varies from 40% to 50% for clear day and around 40% for semi-cloudy day. The overall efficiency of the PVT collector between 55% and 63% for clear-day and around 46-55% for semi cloudy day whereas corresponding top loss value around 3 W/m(2) K for clear day and around 2.5 W/m(2) K for semi-cloudy day. Up to around 3 m from entrance, the plate temperature was increased and then it became nearly steady. But in case of applying same system without PCM temperature was increased sharply. (C) 2015 Elsevier B.V. All rights reserved.