Once connected in the form of a panel, cells must be covered/coated to protect the semiconductor components from physical damage and to prevent direct contact with electrical hazards. C-Si PV cells are protected by a layer of glass, and commercial thin-cell PV panels are sandwiched between glass which not only affects efficiency but is subject to environmental damage much like, but to a lesser extent, the semiconductor components the glass is intended to protect.
Light must penetrate the glass to reach the solar collectors retained within. Despite surface treatment with antireflection coatings, reflection and refraction are unavoidable. In other words, not all the energy that reaches the glass surface of a PV panel reaches the solar collecting cells. This is the nature of the beast! It is unavoidable. Efficiency is reduced by the protective glass covering.
Glass is subject to environmental forces such as hail and flying objects in high winds. Dust storms, which occur in deserts where PV panels and solar thermal mirrors are ideally located, are inevitable. Sand blasted glass and mirrors are not a good thing—efficiency once again compromised.
On flat lands, tornadoes are creatures of destruction—a tragedy in the making for commercial photovoltaic and solar thermal facilities. Nature can wreak havoc on these solar facilities and destroy an expensive power plant with one fell swoop. Talk about blackouts and long term electricity outages! Where a community is largely reliant on solar energy, a fickle flight of nature could have long term impact on energy.
Another problem with glass is that it collects dust and dirt—much like your outdoor window do. This dirt further obscures light. In many cases, a 25 percent obscured surface will reduce the generation of electricity 50 percent. This is problematic. So, the panels must be cleaned on a routine basis, or solar penetration will be prevented and efficiency diminished.
On this note, one might look at the Sahara Dessert Solar Energy Project with a jaundiced eye. There are strange happening around the globe. And environmental, political, and weather conditions appear to be ignored by the investors as they race to a fanciful pie-in-the sky. Far be it for me to judge, but as I see it, the outcome can be and most likely will be financially disastrous.