IMPACT OF THE HEAT POWER ON THE UNIT GEOTHERMAL ENERGY COST; STUDY OF THE GEOTHERMAL POTENTIAL OF NORTH RHINE-WESTPHALIA; GERMANY; Study on Heat Extraction Characteristics by Coaxial Heat Exchanger; THE EFFECT OF USE LOW TEMPERATURE HEATING SYSTEMS ON GEOTHERMAL ENERGY UTILIZATION IN GEOTHERMAL HEAT PLANT; THE PERSPECTIVES OF GEOTHERMAL HEAT UTILIZATION IN DISTRICT HEATING SYSTEM OF KOSICE CITY;