A solar receiver includes a cavity that is operable to receive concentrated solar energy and a heat exchanger in thermal-receiving communication with the cavity. The heat exchanger includes a plurality of thermal capacitors. Each of the plurality of thermal capacitors has a regular geometry. The plurality of thermal capacitors defines open flow passages there between and at least two of the plurality of thermal capacitors have a different size. The plurality of thermal capacitors has a packing factor of greater than 74% with regard to the volume of the heat exchanger.