A step forward towards an ideal absorber for solar energy

With the object of enhancing the absorptivity of water for solar radiation, the effect of dissolved salt was studied. Five saturated solutions were prepared by dissolving the following salts in water: copper sulphate, potassium permanganate, potassium dichromate, cobalt chloride and TMPD. The extinction coefficients of these five saturated solutions were measured in the spectral range 330–1100 nm. The results indicated that a mixture of copper sulphate and potassium permanganate solutions behaves as an ideal absorber for solar energy, in that the percentage transmission in the previously mentioned spectral range is reduced to less than 0.1%. The mixture was tested against distilled water, where the rise in temperature against time shows that the absorptivity for solar radiation is significantly improved. The chemical stability of the mixture was also examined over a long period of time.