A new electrical power source for long term unattended operation

This paper reports results of research at Harwell on thermal energy conversion, which began in 1966 and has led to the successful development of an efficient heat engine/alternator system capable of delivering several tens of watts of alternating current with an efficiency much greater than that of alternative methods. This system has no rotating or sliding surfaces, so requires no lubrication, and is believed to be capable of operating continuously for many years without wear or need for attention. It is capable of using heat from a variety of sources and is self-starting on application of heat. Three electrically-heated research machines have been built and run, the third delivering an output of 27 watts a.c. with an efficiency of 13.5%. Two development machines have been built and are running, one propane-heated and delivering 31.75 watts a.c, and one with a radiation shield for operation with a radioisotope heat source, which delivers 18 watts a.c. Both give an overall efficiency of 10% including all losses from the heat sources.