Hey There: The most important part is that you stop the sun from hitting the glass - this can be done by shutters or solar screens. The shutter system in general is much larger (the casing) than a fabric solar screen. The fabrics are available in different colors and also light transmission - 3%/ 5% and 10%...

Good Luck

There were 2 studies done on the efficacy of exterior solar screens on energy savings. Both are quite hard to find online, unfortunately.

In short - the heat reduction with solar screens that are mounted on the exterior of the window IS significant (as manufacturers and installers of thousands of them in the SF Bay Area, we can confirm).

A PAMA (Professional Awning Manufacturers Association) study showed exterior-mounted retractable solar shades can reduce annual cooling energy costs up to 86% (this was for homes in San Francisco).

You can see the excerpt of that report on the ERS webpage for retractable solar screens here. You can also see some examples of the openness and color factors of the fabrics that we use there.

Another organization, the AERC, reported $ savings to be $10-180 annually for roller shades and up to $270 for solar screens on single pane windows ($40-160 for double pane).

Unfortunately, we're not aware of any similar reports for exterior rolling shutters, but there is one for retractable awnings, found at the latter link, as well. A

A PAMA Energy Study also showed awnings can reduce annual cooling energy 64-80% for homes in San Francisco.

This same study by PAMA also found awnings INCREASE heating costs in colder months as they block natural heat gains when they are extended - another reason to invest in a retractable awning that can be collapsed in colder months!

That study is backed by further evidence from larger, independent organizations:

ASHRAE (the American Society of Heating, Refrigeration, and Air-Condition Engineers) show that an awning reduces solar gain by 72-77% on western exposures, reducing home cooling energy consumption by up to 60%.

The US Department of Energy report solar heat gain reductions of 65-77% from Awning usage.