Radiative cooling surface coatings

1. A surface coating composition for providing a surface coating having radiative cooling properties, the composition including a solar reflective pigment and a quantity of microspheres, said coating having a high reflectance of solar radiation, wherein said quantity of microspheres is effective to enhance the emittance of said coating such that said coating has a high radiative emittance in a wavelength range of 8 to 13 μm to emit thermal energy in said wavelength range.

2. A composition according to claim 1 in which the microspheres are silica microspheres.

3. A composition according to claim 2 in which the microspheres have a shell of silica-alumina.

4. A composition according to claim 1 in which the diameters of the microspheres are substantially between 45 μm and 150 μm.

5. A composition according to claim 4 wherein the average diameter of the microspheres is approximately 50 μm.

6. A composition according to claim 1 in which the microspheres have shell thicknesses substantially between 0.3 μm and 1 μm.

7. A composition according to claim 1 , wherein said composition includes from substantially 60 to 150 kg of microspheres per 600 L of the composition.

8. A composition according to claim 1 , wherein said composition includes from substantially 60 to 140 kg of microspheres per 600 L of the composition.

9. A composition according to claim 1 , wherein said composition includes from substantially 60 to 70 kg of microspheres per 600 L of the composition.

10. A method of reducing temperature within a building relative to ambient temperature, said method including the step of applying a surface coating to the building, said coating including a solar reflective pigment and a quantity of microspheres, said coating having a high reflectance of solar radiation, wherein said quantity of microspheres is effective to enhance the emittance of said coating such that said coating has a high radiative emittance in a wavelength range of 8 to 13 μm to emit thermal energy in said wavelength range.

11. A method according to claim 10 in which the surface coating has a radiative emittance greater than 85% at thermal wavelengths.

12. A method according to claim 10 in which the surface coating has a solar reflectance greater than 80%.

13. A building having a roof with a surface coating having a composition according to claim 1 .

14. A composition according to claim 1 , wherein said coating is adapted to absorb heat and re-radiate said heat as thermal energy in said wavelength range.

15. A composition according to claim 1 , wherein said coating has a radiative emittance greater than 85% at thermal wavelengths.

16. A composition according to claim 1 , wherein said coating has a solar reflectance greater than 80%.

17. A composition according to claim 16 , wherein said coating has a solar reflectance greater than 95%.

18. The method of claim 10 , wherein said coating is adapted to absorb heat from within said building and re-radiate said heat as thermal energy in said wavelength range.

19. A method according to claim 12 in which the surface coating has a solar reflectance greater than 95%.

20. A method according to claims 10 , including the step of applying said coating to a roof of said building.

21. A solar selective surface with a surface coating having a composition according to claim 1 .

22. A composition according to claim 1 , wherein the coating has a radiative emittance greater than 90% at thermal wavelengths.

23. A composition according to claim 1 , wherein the coating has a radiative emittance greater than 95% at thermal wavelengths.

24. A method according to claim 16 , wherein the coating has a radiative emittance greater than 90% at thermal wavelengths.

25. A method according to claim 16 , wherein the coating has a radiative emittance greater than 95% at thermal wavelengths.