Electric System Cascade Analysis (ESCA), an optimisation technique for the design and scheduling of a distributed energy generation (DEG) system based on Pinch Analysis concept is developed with the basis to ensure maximal thermal efficiency of the power generators. By assuming that the power generator will operate at full load at all time, the optimal capacity of the power generator and the energy storage (ES) device including the optimal schedule of the system is revealed. While the generator operates at maximum thermal efficiency, it may results in higher energy losses due to extensive inversion of current, and storage of energy. It also may lead to the needs of larger ES which could be expensive. In this article, the trade-of between generator thermal efficiency and ES-related losses is studied upon. A new set of heuristic is also introduced to discuss on the flexibility of operating the power generator. It is revealed that indeed by increasing the capacity of the generator and allowing flexibility to its operation, the overall efficiency of the DEG system will be higher. As for the economics, the cost of the system increases with increasing capacity of the power generator despite decreasing capacity of ES.