M. Hermann*, T. E. Kuhn, M. Rommel

Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany
* Corresponding Author, Tel.: +49 7 61 / 45 88 — 54 09, Fax: +49 7 61 / 45 88 — 94 09
michael. hermann@,ise. fraunhofer. de

Abstract

The collector proposed in this paper is a semi-transparent combination of a solar collector and an angular-selective sun-shading device. The absorber of the collector features an array of small openings between the channels which lead to angular-selective properties and to a semi­transparent appearance. The casing of the collector is made from transparent materials. For example, the absorber is mounted between two (or more) glass panes. This means that a person inside the building can look through the collector. The complete window-like collector thus acts as a multifunctional building component which uses solar energy for heat production as well as daylighting and simultaneously provides solar control and glare protection. The multifunctional collector described here is in an early stage of research and development. First investigations concentrated on basic construction possibilities and raytracing simulations. The main tasks within the future work will be the evaluation of different feasible absorber constructions as well as an assessment of the component’s behaviour regarded both as a solar collector and as a transparent, window-like building component. An important focus is on architects’ specifications in order to offer them new perspectives for using solar energy in an attractive and innovative way. The work on the development of this new multifunctional collector will be carried out within a European project together with industry partners.

Keywords: Fa? ade collector, building integration, daylighting, shading

1. Introduction

Solar thermal collectors are state-of-the-art, not only as roof installations, but also integrated into fa? ades, where they can replace a part of the wall and its insulation. In contrast to these opaque constructions, the collector proposed in this paper is a semi-transparent combination of a solar collector and an angular-selective sun-shading device. A part of the solar energy irradiated on the building surface is absorbed in the collector and thus reduces the cooling load of the room behind it during summer months. Additionally, the heat gained from the collector can be used to drive a solar cooling system. An impression of how such semi-transparent fa? ade collectors could look like is given in Fig. 1. The semi-transparent appearance is obtained by a number of small openings between the fluid channels. The openings are built in a way which leads to a three-dimensional structure und thus to a shading behaviour which is dependent on the incidence angle of the sun. They can be produced e. g. by cutting and bending small fins or long lamellae between the fluid channels out of the absorber sheet (Fig. 2). There are also a number of other possibilities to produce the openings. The development

and assessment of angular-selective shading devices without the additional function of a solar absorber is an important field of research at Fraunhofer ISE ([1, 2]), and some of theses devices already exist on the market (Fig. 3). Since the tasks of the collector are both gaining solar energy by heating a fluid and protecting the room from overheating, new challenges arise concerning development as well as technically characterizing this new building component in a sufficient and adequate way with respect to all its physical properties.

Fig. 3: Angular-selective sunshade senn® (clauss markisen Projekt GmbH).
The lateral dimensions of each each profile are 4 mm x 5 mm