Consider a flat-plate solar collector on a roof. The inner and outer surfaces of the glass cover are at 28 °C and 25 °C; area 2.2 m^{2}, thickness 0.6 cm, k = 0.7 W/m·°C. Heat is lost from the outer surface by convection (h = 10 W/m^{2}·°C, ambient 15 °C) and radiation. Determine the fraction of heat lost by radiation. (answer in %)