Radioisotope thermoelectric generators (RTG) are used for low-power applications in remote and harsh environments during extended periods of time. They generate electricity from the heat of radioactive source via a series of thermocouples, with a conversion efficiency around 5%.

One possible way to boost the output of a RTG is to use a thermoacoustic heat engine, where the temperature difference generates sound waves which are converted into electricity by a microphone. Their conversion efficiency is about 20-30%.

One interesting possibility is the use of Chargeable Atomic Batteries as the heat source. They are capsules of non-radioactive precursors which are activated inside a nuclear reactor just prior to assembly, making them cheaper and safer than conventional radioactive sources.