  We analyse a device aimed at the conversion of heat into electrical energy,
based on a closed cycle in which a distiller generates two solutions at
different concentrations, and an electrochemical cell consumes the
concentration difference, converting it into electrical current. We first study
an ideal model of such a process. We show that, if the device works at a single
fixed pressure (i.e. with a ``single effect''), then the efficiency of the
conversion of heat into electrical power can approach the efficiency of a
reversible Carnot engine operating between the boiling temperature of the
concentrated solution and that of the pure solvent. When two heat reservoirs
with a higher temperature difference are available, the overall efficiency can
be incremented by employing an arrangement of multiple cells working at
different pressures (``multiple effects''). We find that a given efficiency can
be achieved with a reduced number of effects by using solutions with a high
boiling point elevation.
