Heliostats for maximum ground coverage

Abstract

Most conventional heliostats consist of a rectangular reflector which is moved around a fixed vertical axis tracking the azimuth of the sun and a second moving horizontal axis which rotates around the vertical axis to allow tracking the elevation of the sun. The maximum ground coverage possible of fields of such heliostats without colliding neighbouring reflectors is 58%. Applications of a Multi Tower Solar Array (MTSA) may need heliostat fields with ground coverage over 90%. We propose a new type of heliostat which can be set up in fields with a ground coverage of up to 100%. The maximum possible ground coverage depends on the unimpeded space volume needed by the reflector of each heliostat. The shape and the orientation of this space volume depends on the orientation of the tracking axes and on the shape of the reflector. A horizontal orientation of the fixed axis allows higher ground coverage and heliostats with rectangular reflectors can be lined up in rows with the highest density. The row density increases the longer the reflector becomes relative to its width and approximates 100% maximum ground coverage for infinite long and slim heliostats. With specially shaped hexagonal reflectors, ground coverage up to 100% is possible.