A low profile heliostat with elongated louvered mirror segments is provided. Its envelope of revolution has the shape of a flat disc to enable heliostat fields with very high ground coverage ratio. The heliostat's disc-shaped footprint rotates around a substantially vertical axis (akin to a carousel). The short dimension of the mirror segments is drastically shorter than the disc's diameter. Embodiments are described in which the motion relies on two concentric rings, which are individually rotated around a vertical axis. The lower ring acts as a platform providing mainly azimuth tracking, carrying the upper ring. The differential rotation between the upper ring and the lower ring is translated into a rotation of the mirror segments around a second, perpendicular, axis and used for elevation tracking. Disc-shaped heliostat with D-shaped cut-offs are described, to facilitate the required maintenance access even in highly dense heliostat fields.