A device for quantifying a useful thermal energy available in a tank for storing a heated or cooled fluid or solid includes: a plurality of thermoelectric converters configured to be distributed in plural locations of the storage tank; an electric circuit interconnecting the thermoelectric converters; a device measuring a single electrical variable of the electric circuit; and a converter converting a single measurement of the single electrical variable into a value for quantification of the useful thermal energy available in the storage tank.

A device for quantifying a useful thermal energy available in a tank for storing a heated or cooled fluid or solid includes: a plurality of thermoelectric converters configured to be distributed in plural locations of the storage tank; an electric circuit interconnecting the thermoelectric converters; a device measuring a single electrical variable of the electric circuit; and a converter converting a single measurement of the single electrical variable into a value for quantification of the useful thermal energy available in the storage tank.