The aim of the project is to develop mathematical model of the relationship between incoming solar insolation and PV module output current and temperature. Solar insolation need to be measured in order to optimize the design of solar electricity generating system (SEGS). PV module sizing, battery sizing and also planning of auxiliary back up in order to avoid failure of electricity supply to the load is essential. A proper design of SEGS will lead to reliable and sustainable system to power electrical load. Output power of PV module fluctuates due to nature of solar insolation which varies according to time of the day and also the weather condition. The relationship between input power density of solar insolation and PV module output current and temperature is determined based on experimental design. Solar insolation data is collected by using pyranometer and output PV module current and temperature data are captured using suitable data acquisition system. Through this project, the equation of relationship between solar insolation and output current and temperature PV module is obtained and the equation is used to develop solar insolation measuring device and data logging system. © 2012 American Institute of Physics.