Radiation energy can be converted into electricity by means of i) Conversion of the kinetic energy of nuclear radiation into electric current via conventional heat engines., ii) Direct conversion of the kinetic energy into electricity by the thermoelectric converters., iii) Production of electrical power by exposing the solar cells or thermionic converters to nuclear radiation; and iv) generation of electric current by subjecting the nuclear radiation to an electrostatic field. In a radioisotopic generator employing thermoelectric conversion, the radioisotope acts as a heat source. Overall efficiency of these generations is 10%.