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Written by Anupam 2009
Soltecture (formerly Sulfurcell), a manufacturer of solar modules, has announced the development of a sustainable office building, which proves that solar construction can be both aesthetically pleasing and economic. The complex, which provides space for an administrative building and a production hall, features solar façade cassettes that have been deployed for the first time. The solar cassettes carry hardened, frameless glass, enabling the modules to create a smooth and elegant glass façade. The modules can be installed like conventional cassette cladding systems to generate renewable energy for the building. Since the solar cassettes are installed on a substrate, it becomes possible to clad them on uneven surfaces, such as facades of old buildings as well. The cassettes are rear-ventilated and equipped with recessed drainage channels that release rainwater in a controlled fashion to prevent the thermal insulation from getting wet and also regulate the temperature of the solar modules, thereby increasing their efficiency. The headquarters feature 900 cassette modules, which collectively generate one third of the building’s overall energy needs. The remaining energy comes from a roof-mounted solar array that ensures that the building is completely powered by renewable energy generated on-site.
With its building, which consists of an administrative building and production hall, Sulfurcell and its construction partners are breaking new ground in industrial architecture.
The main design element utilized on the administrative building is provided by the solar facade cassettes, which were deployed here for the very first time. Their surfaces consist of hardened, frameless glass, enabling the modules to create a smooth and elegant glass facade. Black metal spandrels and brown timber banding provide additional highlights. When developing this solution, ease of handling was a decisive factor for Sulfurcell. The modules are hung like conventional cassette cladding systems. Because they are installed on a substructure, this even makes it possible to clad uneven background surfaces, such as the facade of an old building.
The solar facade cassettes are rear-ventilated and equipped with special recessed drainage channels. These discharge rainwater in a controlled manner, thus ensuring that the thermal insulation layer remains dry (see Fig. 5). In technical terms, the rear ventilation has the added advantage that the module temperatures are lowered, thus increasing their energy yields. The 900 cassette modules on the facade supply around one third of the administrative building's energy needs. The remaining energy requirement is provided by the solar power system on the roof of the production hall, ensuring that the administrative building is hundred percent energy-independent.
The Manufacturing Process by Sulfurcell
Sulfurcell develops and produces solar PV modules based on the absorber material Copper-Indium-Sulfide (CIS). Apart from the p-type absorber CIS – this is where the absorbed light is transformed into electric current – a module consists of a second, n-type semicondutor layer, a metallic back contact and a transparent, conducting front contact. Within a module a number of solar cells are series-interconnected.
The most common solar PV modules are based on crystalline silicon as absorbing material. CIS, the material Sulfurcell uses as absorber, has significantly better absorption properties. Therefore, the thickness of a CIS solar cell can be reduced to 1 % of the thickness of a common solar cell based on crystalline silicon.
The various layers a solar module consists of are deposited one after another on a glass substrate. The glass substrate serves twofold, as support for the very thin solar cells and as part of the later encapsulation. For the deposition of the various layers of a CIS based solar PV module techniques such as sputtering are used which have been applied successfully for a long time in the area of large scale glass pane deposition for architectal applications. Using sputtering large areas can be deposited homogenously at low energy consumption.
On the molybdenum back contact precursors consisting of copper and indium are deposited. In the presence of elemental sulfur vapor at a temperature of about 500°C the precursor reacts within a short time to form the absorber material CIS. The device is completed by the deposition of a front contact and after the contacting it is encapsulated to secure it from climatic influences.
In order to realize the integrated series interconnection of a number of cells on one substrate glass the deposited layers have to be disconnected at appropriate spots. This is done typically after the corresponding deposition process. Thus, the fabrication of the solar cells and the solar PV module is combined in one single process chain.