A concentrated solar power (CSP) system includes channels arranged to convey a flowing solids medium descending under gravity. The channels form a light-absorbing surface configured to absorb solar flux from a heliostat field. The channels may be independently supported, for example by suspension, and gaps between the channels are sized to accommodate thermal expansion. The light absorbing surface may be sloped so that the inside surfaces of the channels proximate to the light absorbing surface define downward-slanting channel floors, and the flowing solids medium flows along these floors. Baffles may be disposed inside the channels and oriented across the direction of descent of the flowing solids medium. The channels may include wedge-shaped walls forming the light-absorbing surface and defining multiple-reflection light paths for solar flux from the heliostat field incident on the light-absorbing surface.
 The United States Government may have certain rights to this invention pursuant to contract number DE-AC36-08G028308 between the United States Department of Energy and Alliance for Sustainable Energy, LLC. This invention was developed under subcontract ZGJ-3-23315-01 between Alliance For Sustainable Energy, LLC. and Babcock & Wilcox Power Generation Group, Inc. under contract number DE-AC36-08G028308.