NOVELTY - The work execution method involves operating a first thermodynamic cycle in which heat for a first working fluid is provided by combustion of a fuel-based (FB) energy source. A second thermodynamic cycle is then operated, in which heat for a second working fluid is from a combination of NFB energy source and waste heat from the first thermodynamic cycle. The FB energy source include at least one of a fossil and a bio-fuel. The NFB energy source includes at least one of a solar and a geothermal energy source.    USE - Work execution method using heat from energy systems based on geothermal heat sources.    ADVANTAGE - Provides a system for the conversion of heat into usable energy in the form of electricity, in the form of a heating medium, and in the form of a coolant medium, in which the electricity may be used to drive electrical appliances such as is found in a residence, a commercial entity, or a factory, the heating medium may be used to provide space heating and hot water to a facility, and the coolant medium may be used to supply a cooling supply to air conditioning units in the same settings. Ensures that overall system efficiency may be improved if some fraction of the cooling capacity is supplied indirectly from electricity via the chiller. Includes a control software that can manage a number of sophisticated tasks including optimizing overall system efficiency, and optimizing the efficiency of particular outputs such as heating, electricity and cooling. Ensures that the threshold at which the low-temperature and solar thermal sources can provide useful energy is lowered, and overall energy utilization is enhanced. Ensures that the heat from combustion and solar sources may be used to supplement the heat from the geothermal heat source to provide opportunities for enhanced energy extraction, utilization, and conversion from multiple heat sources.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a heat harnessing method for use on geothermal heat source; and    (2) a heat-to-energy converting apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of an organic Rankin cycle (ORC) based energy conversion system driven by geothermal and solar heat sources.    Thermal sources (200,202)    ORC engine (208)    Generator (210)    Distributor (214)    Chiller (220)