What Is the Difference Between Facade and Rooftop PV Installation?

The integration of PV arrays with buildings can be divided into rooftop installation and facade installation; it can be said that these two installation methods suit most buildings.

Rooftop installation mainly includes horizontal roofs, sloped roofs and PV skylights, among which:

1) Horizontal roofs: On a horizontal roof, the PV array can be installed at the optimum tilt angle to achieve maximum generation; conventional crystalline silicon PV modules can be used, reducing module investment costs, so the economics are usually relatively good. However, the aesthetics of this installation method are average.

2) Sloped roofs: In the Northern Hemisphere, roofs sloping toward due south, southeast, southwest, due east or due west can all be used to install PV arrays. On a due-south sloped roof, the array can be installed at or near the optimum angle to achieve higher generation; conventional crystalline silicon PV modules can be used, offering good performance and low cost, so the economics are also good. Moreover, this does not conflict with building functions, integrates tightly with the roof, and looks better aesthetically. Roofs with other orientations (away from due south) have lower generation performance.

3) PV skylights: These use transparent PV cells as skylight building components. They look very good aesthetically and meet the need for light transmission. However, PV skylights require transparent modules, which have lower efficiency; besides generating power and transmitting light, skylight components must meet certain architectural requirements for mechanics, aesthetics and structural connections, so module costs are high and generation costs are high; they add social value to the building and bring a green concept effect.

Facade installation mainly refers to installing PV modules on the south wall (for the Northern Hemisphere), east wall and west wall of a building. For multi-story and high-rise buildings, the walls are the exterior surfaces with the largest sun-exposed area, and PV curtain walls and vertical PV curtain walls are among the more common application forms. According to design needs, transparent, semi-transparent and ordinary transparent glass can be combined to create different building facades and indoor light and shadow effects. Double-skin PV curtain walls, point-supported PV curtain walls and unitized PV curtain walls are currently common forms of PV curtain wall installation. Modules used for curtain wall installation are relatively costly, the PV system schedule is constrained by the overall building schedule, and because the PV array deviates from the optimum tilt angle, output power is relatively low. In addition to PV glass curtain walls, PV exterior walls, PV canopies, etc. can also be installed on building facades.

(a) Horizontal roof      (b) Sloped roof

(c) PV skylight      (d) PV curtain wall