PHOTON International The Photovoltaic Magazine

Rensselaer develops tracking concentrator systems for office windows

The new intelligent window system, known as Dynamic Shading Window System (DSWS) of New York-based Rensselaer Polytechnic kills two birds with one stone. Not only does the window block direct sunlight, but it also produces electricity: packed between two panes of glass is a kind of PV module, consisting of several dozen 30 × 30 cm PV elements.

	© Rensselaer Polytechnic Institute
Selective: As this computer animation demonstrates, this electricity-generating window blocks direct rays, while diffuse daylight can shine into the room.

The elements themselves contain a Fresnel lenses constructed of plastic and an underlying 1 cm² silicon or GaAs solar cell. The sun-tracking lens system, driven by motors and directed by light sensors, keeps direct sunlight constantly focused on the cells and concentrated at a factor of around 500 suns.

The desired side effect is that the harshest rays are deflected, while the diffuse daylight can still enter the room. Thus the room is always comfortably illuminated. Blinds or curtains are unnecessary. The window currently only exists on a laboratory scale.

© Rensselaer Polytechnic Institute

Prototype on lab scale: The Fresnel lenses concentrate sunlight on tiny silicon or GaAs solar cells.

In the next two years, the institute plans to construct a building-scale demonstration project, but the product won't be ready for commercial sale for another three to five years, says architecture professor Anna Dyson, who helped develop the system. In addition to powering the tracking system's motor, the electricity produced by the window will provide enough energy to heat, cool, and light up the room. The system was especially designed for offices and public structures. According to the developers, the window promises to significantly reduce the burden on America's electricity grid, a topic that has made big headlines since the great blackout of 2003.