Integrating phase change material with building envelopes is recently considered one of the most reliable passive solutions to mitigate indoor temperature fluctuations, improving therefore indoor comfort. In addition, the integration of photovoltaics to combat the gradual increase in energy consumption is highly increasing to meet the growing demand for energy. Using phase change material to improve thermal and electrical performances of building integrated photovoltaic systems and to reduce incoming heat energy indoors, simultaneously, were performed. Interestingly, it is highly recommended to integrate the building integrated photovoltaic phase change material systems on inclined roofs in order to perform the phase change material as preferred through a cyclic process. The peak temperature of the inclined and vertical building integrated photovoltaic systems decreased from 70.5°C and 41°C to 41.4°C and 31°C, respectively. Hence, a drop in average indoor daytime temperature where the peak indoor temperature has been reduced to about 4.5°C. The inclined and vertical building integrated photovoltaic systems’ DC power output, at midday, has been increased from 74.5 W to 108.5 W and 37.5 W to 38.5 W. Eventually, the use of phase change material decreased the thermal load leveling by 7%, 2% and 1.5% during the first three days, respectively, After the third day, the decrease of the thermal load leveling remained constant at 3%. Consequently, findings reveal that using phase change material could be an excellent solution to decrease indoor air temperature fluctuation and can bring higher temperature drops.

High renewable-energy shares do not, by themselves, guarantee that renewable electricity can be absorbed, shifted, and delivered through a constrained network. This study uses openTEPES for a deterministic 8736 h assessment of Tunisia’s 2035 power system, represented by 47 domestic nodes. It compares matched cases without and with endogenous battery energy storage system (BESS) investment and evaluates eight sensitivity families. In the no-BESS case, 265.996 GWh of modelled energy not served (ENS) and 1120.263 GWh of renewable curtailment occur in disjoint hours, indicating a temporal mismatch between scarcity and surplus. Under the central assumptions, the model selects 3.590 GW/14.361 GWh of BESS, reducing modelled ENS to zero under the represented deterministic conditions and renewable curtailment to 42.362 GWh. The sensitivity analysis shows that the model-selected BESS capacity and location, together with transmission exposure, depend strongly on demand, imposed duration, renewable-profile stress, interconnection availability, and candidate siting. Within the modelled scenario space, storage, internal transmission, and cross-border exchange therefore provide complementary forms of flexibility. The central BESS quantity is interpreted as a conditional planning benchmark, not as evidence of probabilistic adequacy or a national procurement target.