# Developments, Trends, and Challenges in Optimization of Ship Energy Systems
## 5 Further Research Needs and Challenges in Optimization of Ship Energy Systems  
### Synthesis Optimization  
#### 5.1.1 On the Possibility of Finding the Optimal Configuration  
In the usual practice, the system configuration is determined by the designers based on their knowledge and experience, while their ingenuity and inspiration can be of vital importance in creating new systems. It is interesting and useful to copy here a paragraph from Ref. [89]:  
_\"Given the multitude of energy system types and the variations in each type, one may question whether it is ever possible to replace the experienced designer's mental process with an algorithm consisting of a set of formulae and rules. On the other hand, in today's complex world, this same multitude of types and variations makes it rather impossible even for an experienced designer to evaluate all possible alternatives. Consequently, an automated procedure, if properly used, can be of invaluable help to the designer.\"_  
The preceding thoughts justify the impetus for development and application of methods for synthesis optimization of energy systems. The related activity for energy systems on land started in the 1980s, while applications on ships appeared in the first decade of 2000. Characteristic classes and examples of methods for land installations are presented in [2,3], while here, we will be restricted to systems on ships. 1.2 Methods and Applications of Synthesis Optimization of Ship Energy Systems-Challenges and Opportunities  
As indicated in Table 2, only 13 of the 57 articles address the synthesis optimization problem. In 11 of these articles the superconfiguration (the term \"superstructure\" is used in the literature on land systems, but it is avoided here, because it has a different meaning on ships) approach is followed, i.e., all the envisioned components are possible candidates for the system and a synthesis independent variable is associated with each component. It may be a binary variable (0, 1) indicating whether a component exists or not in the optimal configuration, a continuous variable (e.g., the nominal power of equipment) with zero value indicating nonexistence of the component in the optimal configuration, as well as integer variables indicating connections between components. In No. 4 [39] the optimum ORC process layout and fluid are determined out of a number of fluids available, while the method includes four processes: (a) at subcritical and supercritical pressures, (b) with any degree of superheating, (c) with or without internal recuperator, and (d) with and without preheater. Broadly speaking, this is similar to the superconfiguration approach. \begin{table}
\begin{tabular}{l c} \hline
**Algorithm** & **Articles** \\ \hline \hline
**Hybrid algorithms** & \\ \hline Improved Sine Cosine Algorithm (ISCA), combined with Harmony Search & 54 \\ \hline Hybrid of Grey Wolf Optimizer and Fuzzy Logic Expert System & 34 \\ \hline
**Algorithms dedicated to multiobjective optimization** & \\ \hline Multiobjective Particle Swarm Optimization (MOPSO) & 8 \\ \hline \(\epsilon\)-constraint method & 49 \\ \hline \end{tabular}
\end{table} 
Table 5: _Cont._Completely different is the method applied in No. 17 [51]. The HEATSEP method [90] is used for optimization of the heat exchanger network of the ORC system. The method has been developed for land installations, but it can very well be used for systems on ships. With the continuous increase of interest in and need of integrated energy systems on ships, the installation of pollution abatement equipment, and the appearance of renewable energy equipment on board, the application of synthesis (together with design and operation) optimization will be not a luxury but a necessity. The interested reader is kindly referred to recent reviews in [2,3] for methods and applications of synthesis optimization, primarily on land installations, but they can be applied on ship systems too. With the superconfiguration approach, the optimal configuration inevitably is restricted by the initial superconfiguration.