Energy and exergy modelling of the integration of two black start diesel engines (BSDE) and the combined cycle gas turbine (CCGT) analyses the possibilities of using exhaust gas heat and cooling water heat released by working of two BSDEs and in the existing system discharged into the environment. In the case of a non-voltage start-up, two BSDEs can provide not only electricity, but also thermal energy for heating the high-pressure drum (HPD) of the heat recovery steam generator (HRSG), which is essential for a fast-cold start of the plant. Since the gas turbine does not have a direct discharge of flue gases into the environment, it does not have a bypass stack, all flue gases travel through the HRSG. However, for a fast-cold start of the system, it must be preheated to at least 393 K according to the HPD of the HRSG manufacturer’s instructions. In addition to using the heat of the exhaust gases to preheat the HPD, the heat of the cooling water of both BSDEs is also used for the purposes of heating the buildings. The advantage of using the heat from the exhaust gas and cooling water of BSDE is, therefore, reflected in increased energy and exergy efficiency, which permits the use of BSDE in other cases of increased demand for electricity as well. A vital aspect of the optimization is the secure supply of heat to the HPD, which cannot be provided by the existing auxiliary sources in the event of a power grid failure. The energy and exergy modelling of BSDE integration in CCTG has shown that it is possible to maintain the temperature in the HPD needed for fast starting the CCGT installation by additionally installing a heat transfer in the BSDE exhaust system. The results show that two BSDEs can exhaust gases, heat an HPD up to 393 K as fast as in 16 minutes. The heating time, however, depends on the load of both BSDEs. The use of heat from both BSDEs also increases the energy efficiency by an average of 35.96 % and also increases the exergy efficiency by an average of 14.05 %.