The purpose of writing this article is to find out the power reduction per degree Celsius in a 30 Wp solar panel and the effort to handle it through water cooling. The solar panel is placed on a vertical holder with a hose is mounted on top side of the solar panel. The hose is perforated every 10 cm to drain the water to the front side of solar panel. Two units of halogen lamp of total 600 Watt are used to irradiate and heat the surface of solar panel. The halogen lamps are positioned in front of the solar panel at 32 cm. Three units of thermocouples are attached at front side and three units at back side of solar panel to measure temperatures. Besides, we measure the ambient temperature using a unit of thermocouple. The data of temperatures are collected using NI cDAQ-9174 hardware and LabView software. The average value of low temperature is 39.62 °C and the average value of high temperature is 61.39 °C, while these values correspond with the maximum output power of 7.13 W and 6.59 W, respectively. The power will decrease at magnitude of 0.025 W/ °C. Therefore, water cooling on the surface of solar panel can decrease temperature and increase power output.