## 4 Case Study
### Simulation Results and Discussion
#### 4.2.3 Discussion  
To compare the performance of the optimized layouts, the detailed information of each scenario using MBA, BA_FREE or BA_MIN is listed in Table 1. The detailed information of the cable connection scheme of each scenario is given in Tables 15 and 16.  
It can be seen in Table 1 that the total cost of the cable connection layout found by BA_FREE is lower than the one found by the BA_MIN in each scenario. Although there is little difference between the trenching costs of cables of the solutions obtained by BA_FREE and BA_MIN, the difference of the cable purchasing cost and the power loss cost are obvious. In each scenario, it can be seen that the cable connection layouts have small differences, which means that the cable connection layouts found by BA_FREE and BA_MIN are similar in each scenario, and the cost difference is mainly determined by the cable type selection, which can be seen in Table 1 in that the cost of cables in BA_FREE are higher than BA_MIN in all scenarios. However, by using BA_FREE, more power loss-associated costs are saved compared with using BA_MIN, which saves 404.26 kEUR and 158.42 kEUR, respectively, in scenario I and II. This exactly explains why the total cost of cable the connection layout solved by BA_FREE is always lower than that obtained via BA_MIN even with a similar cable connection layout. Besides this, it can also be noticed that bigger cables with higher expenditures are adopted by the BA_FREE. Taking the 25 operational years into account, the power loss-related cost would exceed the cost of purchasing the cables. Hence, by selecting bigger cables, the BA_FREE method succeeds in lowering the total cost by 2.29% and 0.47%, respectively, compared with the layout obtained using BA_MIN through scenario I and II.  
On the other hand, it can be noticed that the overall cost of the layout obtained by the BA_FREE is smaller than the layout obtained by the MBA, which saved 10.52 and 37.33 kEUR, respectively in scenario I and II. It can be seen that the higher cable purchasing cost, with a 13.17 kEUR increase, is required for the layout obtained by the MBA compared to the layout obtained by BA_FREE in scenario II. This is because the layout found by the BA_FREE has crossed cables. To ensure an uncrossed cable connection layout, as shown in Figure 10a, another layout is selected by the MBA, thus increasing the overall cable purchasing cost.  
Figure 12: Total cost corresponding to each second of Scenario II.  
However, both the BA_FREE and BA_MIN method cannot guarantee an uncrossed cable connection layout, as shown in Figures 7 and 10. In such a situation, savings of 10-40 kEUR do not make sense. For one thing, this will delay the cable installation time. It usually requires 3 to 4 days to place crossed cables, and the cost of a cable ship is about 100 kEUR/day. For another, it increases the cable failure rate, while the energy losses and maintenance cost due to a fault within the offshore wind farm can be up to several million EUR. Hence, the proposed MBA algorithm, which considers both the power loss impact and the strategy of an uncrossed cable connection layout, has profound significance and value in the real application.