A low-power device, simulating a section from a megawatt-output generator, has been built to test a new idea for the arrangement of thermoelements around a cylindrical pipe. The device uses bismuth telluride type thermoelements and operates between a condensing vapour source at 250° C and a sink of cooling water at about 20° C. The maximum measured efficiency was 2.1% at 13 W output. The low efficiency is due partly to high contact resistances inside the generator, partly to the use of low-thermal-conductivity material (stainless steel) for the body of the generator, and partly to a thermoelectric figure of merit giving zT of about 0.6. Until these factors are improved, an efficiency greater than 2.5% cannot be expected theoretically. By-pass heat losses appear to be insignificant, and improvements in contact techniques and use of a material such as copper for the body of the generator should lead to efficiencies of about 5%.