U.S. patent application 20170010023 (applicant Massachusetts Institute of Technology, Cambridge, Mass.):

“Systems and methods for concentrating and storing solar energy are provided. A solar energy receiver for use with the systems and methods may include a container for holding a solar absorption material, such as a phase change material, and a cooled cover disposed above the container for condensing and collecting vaporized phase change material collected along an underside of the cover.”

http://www.freepatentsonline.com/20170010023.pdf