Following some ten years of planning and an international architectural competition, the Mont-Cenis Academy was built between 1997 and 1999 in the town of Herne in the state of Nordrhein-Westfalen, Germany. Located some 60 km northeast of Düsseldorf, the town is in the historic industrial and coal mining heartland of Germany. The educational academy is situated atop the old Mont-Cenis coal mine. With its environmentally and technically groundbreaking design, it is an internationally acclaimed landmark and serves as a symbol of the region's ecological and economic renewal.

Among many other energy and environmental innovations, the most prominent feature of the 12,000 m2 facility is its "micro-climatic envelope", a vast exterior shell of glass and semi-transparent PV modules. This shell encloses a number of buildings and structures that comprise the centre's lecture halls, meeting rooms, civic hall, library, gymnasium and other facilities. While the buildings themselves are heated in the winter, the space inside the glass envelope is not. Large-scale mechanized ventilation controls and the strategic variation of PV cell densities for shading is employed to create a mild Mediterranean micro-climate for the urban environment inside the glass shell.

The PV modules serve a variety of key functions in this design: aesthetically appealing roofing material, shading control that regulates the intake of solar heat and light, and electricity generator. The total capacity of the Building Integrated Photovoltaic (BIPV) system is 1,000 kWp, making it the largest in the world at the time of its construction.

The BIPV system generates some 2.5 times more electricity than is consumed by the facility. Most of the power is thus sold to the central grid. The German Renewable Energy Law (Erneuerbare Energien Gesetz - EEG) promotes grid-connected PV systems by guaranteeing a fixed premium purchase price for PV-generated electricity for 20 years. This significantly improves the cost effectiveness of the Mont-Cenis Academy large BIPV system.

The BIPV system, as well as the overall micro-climatic envelope, has operated well since the project's construction.

System description

Nearly 10,000 m² of the roof's surface is made up of 925 kWp semi-transparent PV modules. Each module is tilted slightly (5º) south. Another 75 kWp of PV is installed vertically on the west-facing façade of the structure. Several different types of multi-crystalline PV cells are used, all of them manufactured by Solarex and ASE. Some 569 individual Sunny Boy 1500 inverters (1,500 W each) are installed in multiple series strings to deliver the solar electricity to the Mont-Cenis buildings and to the grid.

Lessons learned

Photovoltaic cells integrated into a building envelope can serve a variety of functions (e.g. weather skin, shading, day lighting and power generation), thus significantly increasing their value and cost-effectiveness.

Large PV projects allow for economies of scale and can result in low overall per-kWp costs.

Unforeseen factors such as higher than expected temperatures below the roof-integrated PV modules and slight shading due to the saw-tooth configuration of the tilted modules may account for some loss of performance from the overall array.

The use of multiple small inverters allows for easy replacement of defective units and eliminates the large periodic costs associated with the failure of large centralized inverters.

A large BIPV installation can be a cost-effective and attractive showpiece of environmental sustainability and technological sophistication for a community.

The big picture

Worldwide, installed photovoltaic capacity has been increasing by 20 to 30% annually since the mid 1990s. PV systems now supply the equivalent electricity needs of over 1 million homes. Much of this growth has been fueled by European, and particularly German, governments' resolve to establish PV as a significant energy supply option. As a result, module and system costs continue to drop while the efficiency and variety of PV products increases. Building Integrated Photovoltaic systems (BIPV) offer increased application flexibility and cost effectiveness by utilizing PV modules not only for electricity generation but also as a valuable and attractive building material.

© Minister of Natural Resources Canada 1997-2009
www.retscreen.net