As a sustainable and cost-effective solution of energy supply in remote areas, stand alone photovoltaic (SAPV) systems are widely used after the exploding development of photovoltaic cell industry in recent years. A wide variety of computer software tools are available for the dimensioning, analysis and optimization of solar energy systems. This thesis investigates the reliability of specified software tools using the methodology of comparing the measured data and simulation results. Two stand alone photovoltaic systems were established. One has a conventional regulator and the other with a maximum power point tracking (MPPT) regulator. Their operation parameters were monitored and stored with data acquisition tools. A survey concerning the software tools that are capable for SAPV systems simulation was implemented to select the appropriate software to be investigated. TRNSYS 16 was selected to simulate the PVSA systems due to its modular structure and tremendous flexibility. The measurement results have shown that the MPPT system couldn’t produce reasonable energy when the radiation is low. This enlarged the PV energy errors of MPPT system together with the ideal MPPT output from simulations. On the contrary, the inconsistence of charging control between reality and simulation, which was affected by the fractional state of charge (FSOC) and battery voltage, was the dominating reason of PV energy errors of conventional system. Battery efficiency which was used to calculate FSOC became an important parameter in the simulation of charging/discharging control. All to all, the errors were either coming from the real operation or the simulation of regulators. The comparisons of simulations and measurements have also shown that the one diode equivalent circuit model could correctly simulate the electrical performance of solar cells. Whereas the inbuilt thermal model of the solar cell and the battery model still need to be improved.