The following is a paper by H. Aspden published in Speculations in Science and Technology, v. 13, pp. 295-299 (1990).
Abstract: The technological feasibility of converting radiant heat into useful power is discussed. it is shown that a mirror focusing system involving thermal energy feedback can, in theory, be used in conjunction with a Stirling engine to convert heat into electricity with an efficiency close to 100%. There is no limt imposed by the Carnot cycle efficiency because the lower operating temperature is that at which heat energy is supplied as input. If, as is believed, photons really are the carriers of energy, then a solid-state configuration with enhanced power generating capacity is possible once an efficient miniature-scale thermoelectric power conversion device currently under development is commercially available.
Commentary: At the time the subject article was written the regenerative energy technology based on the Strachan-Aspden thermoelectric invention (U.S. Patent No. 5,288,336) [1994a] had been successfully demonstrated and it was hoped that the development interest would progress rapidly. However, circumstances unrelated to the merits of the invention set the project back and this author is, at this time, trying to engender interest by corporations with the necessary R & D, manufacturing and marketing resources. See the Abstract of Energy Science Report No. 3 in these Web pages. [1997b].