The absorber surface of a solar collector is made of aluminum coated with black nickel oxide (a/= 0.92 and = 0.08). The collector is to be installed in Stellenbosch (South Africa). The air and the effective sky temperatures are 20 and 7C, respectively, and the convection heat transfer coefficient is 15 W/m.K. For an absorber surface temperature of 60C, determine the net rate of solar energy delivered by the absorber plate to the water circulating behind it.