In this article, heat loss reduction and overall performances improvement of a solar collector by using Phase Change Material (PCM) are examined. In authors' previous studies, a building-integrated solar collector has been presented with an experimental characterisation and a validated numerical model. In addition, thermal losses at high reduced temperatures were identified due to the specific collector shape. On the other hand, several authors introduced PCM thermal storage for domestic hot water systems (DHWS). In the frame of the present study, the goal is to use the high PCM volumetric thermal density for limiting both temperature and thermal losses and recovering a part of the stored heat during evening. Adding PCM might change the optimum operating conditions: the influence on monthly performances of existing PCM characteristics, flow rate variation, temperature regulation and PCM volume addition are investigated. Simulations for a complete DHWS have been performed with measured environmental data (solar radiation, wind, ambient temperature). The mathematical model of PCM thermal process is presented. The performances with PCM addition are evaluated and the improvements on the thermal behaviour are estimated. In addition, Life Cycle Assessment (LCA) is performed in order to examine the influence of PCM use on the environmental profile of the solar system. (C) 2017 Elsevier Ltd. All rights reserved.