Solar Windows
For what are they good?

Solar Windows are performing a dual task. They serve as traditional windows and as solar panels

Solar Windows and Building Integrated Photovoltaic

The building-integrated photovoltaic concept is to make a dual usage of the building elements. Examples are solar tiles and solar power generating windows. The idea is to embed thin transparent pre-wired active solar cells between two layers of glass. The glass is cut and framed to form windows and to produce electrical power. There are two advantages to this approach:

1. The windows fit nicely with the contour of the building with no visible external solar panels
2. A saving factor because the windows are used for their original purpose (bringing natural light into the house) and also produce electricity

Solar transparent windows focused market is BIPV and zero energy home (mostly a built-to-order sub market).
Therefore, you don't see it yet offered for upgrading existing homes. I expect however to see a penetration into the home improvement market once the technology is mature, standardized and more cost effective
In the building-integrated photovoltaic sub market, a prominent company is Ertex-Solar (Germany)

Innovative Research

The Queensland University of Technology (Australia) cooperated with Dyesol to develop an innovative technology that imitates photosynthesis. The panel is a transparent sandwich of an electrolyte, a layer of the white pigment Titania (Titanium Dioxide), and ruthenium dye (Ruthenium is a white hard metal) inserted between two glass sheets. Sun radiation hitting the dye excites electrons which are absorbed by the Titania to produce electric current. It will take a few years for the new technology to hit the market commercially