In photovoltaic (PV) cells, a fraction of the incident solar energy is transformed into electrical energy. Most of the part is transformed into heat which elevates the cell temperature resulting in reduced electrical efficiency. A box containing phase change material (PCM) can be attached on the dark side of the PV panel to reduce the operating temperature of the PV which elevates the electrical efficiency. In the current work, a mathematical model is presented for analyzing the electrical and thermal performances of only PV and PV-PCM systems at South West UK. Ansys-Fluent software has been used for carrying out the calculations. The results show that, for the June month at Cornwall, UK (50.17°N, 5.12°W), (a) the integration of PCM box at the back of a roof integrated 4kWp PV system decreases the PV temperature by 20°C near noon, (b) the electrical output is improved from 2.6kW to 2.9kW using PCM near noon and (c) the total daily electrical output is increased from 17.7kWh/day to 18.9kWh/day using PCM.