Andreas Fieber, Division of Energy and Building Design,

Department of Construction and Architecture, Lund University P. O. Box 118, 221 00 Lund, Sweden andreas. fieber@ebd. lth. se Phone +46-46-2227347 fax +46-46-2224719 Helena Gajbert, Division of Energy and Building Design, Lund University Hakan Hakansson, Division of Energy and Building Design, Lund University Johan Nilsson, Division of Energy and Building Design, Lund University Tobias Rosencrantz, Division of Energy and Building Design, Lund University Bjorn Karlsson, Division of Energy and Building Design, Lund University

The building industry and the solar energy industry calls for innovative and attractive building integrated active solar thermal and PV systems, in order to widen the acceptance and use of solar energy. As an answer to a widened understanding of building integration, a multifunctional wall element has been developed.

A PV/T component on the inside of an antireflective insulation window with concentrating mobile reflector screens makes the system fully integrated into the building, even its interior. The Solar Window provides PV electricity and warm water, besides passive space heating and day lighting. Simultaneously, the reflector screens act as sunshades and added internal insulation for the window. The reflectors have an optical concentration factor of 2.45, which decreases the required, cost-intensive PV cell and heat absorber area. The hybrid technology has synergetic effects such as cooling the PV cells for increased performance, and making use of heat generated in the cell. The climate protected system is a visible element in the exterior and particularly in the interior, and its performance is directly connected to the user behaviour, due to the operation of the reflectors, which can be switched between a closed, concentrating mode or an open, transparent mode.

Performance of a 1 m2 prototype of the system, regarding its sun shading and U-value properties and its photovoltaic and active thermal output, has been measured. For a two-pane anti-reflective window, the U value is reduced from 2.8 to 1.2 W/ m2K with the reflectors closed. The annual transmittance through the window is estimated to 609 kWh/ m2, of which approximately 10% is expected to be delivered by the PV modules. About 20 % will be delivered as active solar heat and 30% as net passive space heating. The distribution is highly dependent on the daily operation of the reflectors, which to some extent could be automated.