NOVELTY - A metallic reflective film (42) is deposited in the sidewall of cover glass (26) to form a mirror which reflects incident radiation that enters the cover glass through upper surface (30) to the active area (40) of cell (25) by double reflection. The film (42) is coated with silicon oxide to optimize reflection.    USE - For use in terrestrial and space power arrays to generate electric power.    ADVANTAGE - Has modest concentration with broadened tolerance of the tracking angle. The cover glass has minimum mass and directs incident radiation to the active area of the cell using a sidewall mirror for concentrating radiation.    DETAILED DESCRIPTION - The concentrator has a cover glass (26) adhered to a photovoltaic cell (25) using an optical adhesive (28). The lower surface (32) is equal in area to the active area (40) of the cell to funnel light to the cell for efficient conversion. A peripheral mirror surface (38) on the cover glass includes a reflective metal film (42) made of silver, aluminum or rhodium reflects electromagnetic radiation of the desired band of wavelengths. The concentrator has a cover glass (26) which has a minimum thickness necessary to protect the cell from harmful radiation and to concentrate the incident radiation to about 4.5 suns. The upper surface (30) has a surface area greater than the area of the lower surface (32). The reflective film (42) is protected with an exterior, silicon oxide overcoat to optimize reflection of incident radiation and to protect the metal film from oxidation. The upper surface and the lower surface are parallel and both have the same shape. The cover glass is frustoconical and has a side wall connecting the upper surface and the lower surface.    DESCRIPTION OF DRAWING(S) - The figure shows the cross-sectional view of a solar-cell concentrating cover glass combination.    Photovoltaic cell (25)    Cover glass (26)    Optical adhesive (28)    Upper surface (30)    Lower surface (32)    Active area (40)    Mirror surface (38)    Reflective metal film (42)