Abstract: Solar heating apparatus comprises:(a) a generally horizontally elongated tank to contain liquid, the tank being solar radiation absorbing, and low intensity infra-red emitting,(b) a generally longitudinally horizontally elongated container extending about the tank, the container including glazing having a first section facing the top length of the tank, and a second section facing a front side length of the tank, the glazing sections adapted to pass solar radiation for impingement on the tank,(c) auxiliary panels having extended positions in which they project generally away from the container, and collapsed positions in which the panels substantially cover said first and second sections of the glazing to block heat loss from the tank at night,(d) the panels having reflecting surfaces for reflecting solar radiation toward and through the glazing in said panel extended positions,(e) and means responsive to the intensity of solar radiation to move at least one of the panels between extended and collapsed positi