Results are reported from tests of flat-plate solar collectors with various honeycomb structures, and recommended temperature ranges are given for their use. A change in the angle of incidence of solar rays on the surface of a flat-plate solar collector with a honeycomb structure does not affect the efficiency of its operation. Heat losses from a solar collector with a honeycomb structure do not depend on its slope to the horizon, which makes it possible to recommend the use of honeycomb structures for flat-plate collectors of solar energy in any region, regardless of local latitude.