Solar Architecture: Green Glass

Solar Architecture: Green Glass

Glass by serving as a thin-film photovoltaic module that actively generates environmentally friendly electricity can fulfill a protective function of the building as well as make an energy contribution.

By Lars Waldmann

Building shells like roofs and facades need to be able to meet special demands. They must be able to protect against winds and weather, provide shade in the summer, as well as sound insulation. These are all demands that glass meets in architecture today. Nevertheless, the architecture of the future demands more: a building shell should not only fulfill a protective func­tion, but also actively make an energy con­tribution. After all, ecology and sustainable building are turning out to be a megatrend in both architecture and city planning. Here, glass can leverage entirely new strengths as a building material by serving as a thin-film photovoltaic module that ac­tively generates environmentally friendly electricity.

Architects can combine functionality and esthetics extremely well with solar glass, for example, as transparent facade glazing, insulaed roof glazing or ventilated cold facades.

Glass, Its Role in a PV Module

But how can glass become a producer of electricity and what role does it play in a photovoltaic module? One thing the two have in common is that silicon is a main ingredient of both glass and photovoltaic cells. In order to produce the so-called thin-film solar modules, the silicon is pre­pared as a gas and then deposited onto a glass plate. Here, hyperpure white glass panes that are hardened and partially toughened are used. The resulting active silicon layer on the glass plate is less than a micrometer in thickness. Then, a fine laser structures the silicon in such a way that many small solar cells are created. Trans­parent conductor circuits see to it that elec­trons are transported to the cable connec­tions on the module. Once the contacts and the integrated serial connections to the in­dividual cells are applied by laser, this re­sults in a raw, yet functional module. The individual cells on the base glass are con­nected together directly to form a module. Several modules are then connected to­gether to form strings inside the applica­tion. They guide the direct current to an al­ternating-current converter. This converts direct current into alternating current that is then fed into the public power grid. Now that feed-in legislation has been passed, the government ensures that generating and feeding in solar power is always rather lu­crative by guaranteeing operators in Ger­many attractive compensation for a time frame of 20 years for each kilowatt hour of solar electricity that he produces on his roof. In Spain, feed-in remuneration is even guaranteed for 25 years. The calcula­tion is rather simple: the more electricity the modules are able to collect from the light of the sun and the longer they func­tion without difficulty, the more worth­while it is to invest in a photovoltaic sys­tem. Of course, the modules need to be of high quality and quite durable.

Combining Function and Design

As this suggests, the first demand placed on photovoltaic modules is technological performance. From an architectural per­spective, two additional aspects deserve mention: for instance, the solar module needs to replace the shell of the building and take on the protective function of a fa­cade or a roof. In addition to these func­tional demands, the design factor also plays an important role. Today��s percep­tion of photovoltaics is generally dominat­ed by other conceptions: dark blue mod­ules that are installed later on top of single family houses or larger buildings as so called roof-mounted systems. This, how­ever, does not live up to the design demands previously described. However, so­lutions are, in fact, available, because thin-film technology offers a wide variety of design possibilities. Architects can com­bine functionality and esthetics extremely well with solar glass, for example, as trans­parent facade glazing, insulated roof glaz­ing or ventilated cold facades. Preparing glass and photovoltaics as a construction element requires considerable engineering skills and many years of experience.

The German company SCHOTT Solar that is part of the international technology group SCHOTT has bundled its expertise in manufacturing glass and the efficient use of solar energy inside this subsidiary. The company has been active in the thin-film module market since the industry was born and started developing and manufac­turing so-called ASI modules on the basis of amorphous silicon back in 1980.

In explaining why thin-film modules and the ASI Series in particular are predestined for integration into buildings, thin-film modules are capable of generating more energy from sunlight, even with weak and scattered light than crystalline modules. They are, therefore, particularly well-suit­ed for applications with extreme angles of inclination, such as facades, for example. In addition, the ASI glass assumes many functions for modern solar architecture: as a frameless ASI THRU or ASI OPAK module. Their homogeneous, nearly black surface opens up a wide range of design approaches.

Ideas Gained from Practical Experience

The Stillwell Avenue Station project in New York City in the U.S. clearly reveals what is possible with thin-film technology. This is home to what is currently the world��s largest building-integrated PV sys­tem based on thin-film modules. Many people have rightfully referred to the pro­ject as the ��superlative solar roof��. And, in fact, the roof of the train station is a suc­cessful model for the future, both in terms of its architecture and power technology. The roof of the Stillwell Avenue Station building consists of 2,800 thin-film mod­ules from the German vendor. Each year, these produce 250,000 kW hours that are consumed on site by the train station. In the summer, this system covers two-thirds and in the winter one-sixth of the power needs. The unique thing about this project was that no more individual modules had to be installed on the roof, but rather sever­al raw modules were laminated onto larger glass substrates, whereby several of these base glasses were joined together by an aluminum frame. The architect selected the composition of the base glasses in such a way that transparent gaps result. In this way, the roof offers shade, yet allows for 20 to 25% of the light to pass through it. The solar roof of the Stillwell Avenue Sta­tion was completed in 2005. Since then, it has inspired many architects to remain contact SCHOTT Solar and take a closer look at projects of its own involving build­ing-integrated photovoltaics. Schott Solar consider itself to be a partner when it comes to sustainable, responsible construc­tion and try to work with architects on de­veloping standards that everyone can use, but yet leave enough room for customized design.

After all, the potential that thin-film technology holds is far from being ex­hausted.

Lars Waldmann is Public Relations Manager of SCHOTT Solar AG (www.schottsolar.de).