The roof MaReCo, previously described by Adsten (2002), is 2D, concentrating solar collector intended to be placed on a tilted roof, see figure 3. It has a reflector designed as a parabola combined with a circular section and an absorber that absorbs irradiation on the back side from an acceptance interval between 0° and 60° solar altitude angle, when placed on a roof with 30° slope. The absorber also receives direct irradiation on the absorber. A prototype of this design was evaluated by indoor and outdoor measurements of thermal performance at varying incidence angles. The glazing of the prototype was replaced by a Teflon film.

The other concentrating solar collector evaluated here is a hybrid solar window, which basically consists of a parabolic reflector and a hybrid absorber, designed with a

concentration ratio of 2.45. The function of the reflector is both to concentrate the irradiance onto the absorber and to be used as solar shading, as the reflectors may be rotated backwards, as shown in figure 4. The hybrid absorbers consist of thermal absorbers with photovoltaic cells laminated on the surface. The wall element is further described by Fieber et al. (2004). The efficiency of the thermal absorbers in a prototype of this design was evaluated by indoor and outdoor measurements at varying incidence angles. The glazing of the prototype consists of two anti-reflex coated glass panes.

Figure 4. The hybrid solar window.