Whole cities or individual houses can be cooled by making their surfaces more reflective for example by painting them white. This is a cost-effective method that has been used in many hot countries for thousands of years.

The approach can be combined with adding some heat insulation into the buildings. The combination of a shining white surface and a silica aerogel layer under it can already cool the building effectively. However, with present technologies increasing the reflectivity of the buildings and equipping them with PV or PVT panels are alternative approaches, excluding each other.

It might, of course, be a good idea to investigate whether it would be possible to combine both approaches. It might be possible to develop transparent solar panels which would first utilize certain wavelengths to produce electricity and then reflect the rest of the solar radiation back to space, to provide a maximized cooling effect. Unfortunately, we do not have anything like this in the market, yet.

Another problem is that white surfaces have a strong cooling impact also during winter, and not only in summer. This may be a problem, if the winter is cold. If the white surfaces increase the need for heating energy during the winter, part of their climate benefit is lost during the cold season.  Also, the bright reflection from the shiny white surfaces makes it difficult or impossible to use a roof for anything during the daytime, before the sun has set.

One possibility would be to equip suitable roofs and walls with easily installed tiles or plates, that would be black from one side and white from the other.  The tiles could then be turned twice a year, so that the black side would be up during the winter and the white side during the summer. This would provide a cooling effect during the hot seasons and a heating impact during the coldest part of the year.  The tiles or plates should, ideally, consist of an effective heat insulation material, like silica aerogel.