Solar energy is a very attractive renewable source of energy than other renewable source of energy due to relative small system size, free and sustainable generation source or fuel, noise free operation due to the absence of moving parts, the possibility to put it close to the user, ease of installation and systems require relatively little regular maintenance. But the efficiency of solar Module energy conversion is low because it is affected by solar insolation temperature and load conditions. If the load is directly coupled to the PV module, the size of PV modules or the number of PV modules must be increased to supply the required power to the load. This leads to wastage of power, increased cost and an over-sized or require more number of modules to supply the load. In this thesis Modeling and performance evaluation of existing solar powered water-pumping system installed at Merawi kolella kebele in Ethiopia is presented. The proposed system model and evaluate the performance of the existing system at different value of surrounding temperature and solar insolation and propose a solution that reduce the effect of variations of atmospheric on output of the system. After modeling and evaluating the performance of the existing system P&O maximum Power point tracker boost converter is modeled and designed. The P&O maximum power point tracker harvests the maximum available power from the solar array by sensing the current and voltage of the PV array and sends the command signal to adjust the duty cycle of the boost converter. The boost converter then regulates the output voltage, current and power to the desired point. There is a proportional integral (PI) controller to minimize the error between the reference voltage and the measured output voltage. In the proposed systems P&O maximum power point tracker extract or harvest the maximum available power of 2507 watt and produce output voltage of 300V and output current of 8.356 A from the solar array and the boost converter regulate this outputs to a constant value. It increases the power by 1657 watt, voltage by 84 V and current by 1.056 A from the previous system. At the end proposed systems supply power continuously, reduce power loss caused by variation of solar insolation and temperature and reduce cost. The simulation is done in Matlab simulink software.