This paper proposed a new function of photovoltaic thermal (PVT) module to produce nocturnal cool water not just only generating electrical power and hot water during daytime. Experimental tests were carried out under Chiang Mai tropical climate with a 200 Wp monocrystalline PVT module having dimensions of 1.601 m × 0.828 m connected with two water tanks each of 60 L taken for hot and cool water storages. The module was facing south with 18 o inclination. The electrical load was a 200 W halogen lamp. From experiments, by taking the module as a nocturnal radiative cooling surface, the cool water temperature in the cool storage tank could be reduced 2 o C-3 o C each night and the temperature could be reduced from 31.5 o C to 22.1 o C within 4 consecutive days. The cool water at approximately 23 o C was also used to cool down the PVT module from noon when the PVT module temperature was rather high, and then the module temperature immediately dropped around 5 o C and approximately 10% increase of electrical power could be achieved. A set of mathematical models was also developed to predict the PVT module temperature and the hot water temperature including the cool water temperature in the storage tanks during daytime and nighttime. The simulated results agreed well with the experimental data.