4.3.3. Total Costs Comparisons with Different P

The economic costs of various transmission concepts are sensitive to transmission capacity, as shown in Figure 5. In near sea wind energy transmission, the economic costs of GIL transmission for 900 MW wind farms are even lower than that of VSC-HVDC transmission near sea wind farm transmission due to its advantages of large-capacity transmission. Thus, the GIL concept may be a better choice in the scenario under short distances with large-capacity transmission.

**Figure 4.** Cost component comparisons with different *L* (*P* is 300 MW): (**a**) shows the HVAC system; (**b**) shows the VSC-HVDC system; (**c**) shows the GIL system; (**d**) shows the Hybrid HVDC system.

**Figure 5.** Total costs of different P of 25 km, 50 km, and 75 km wind farms: (**a**) shows the 25 km offshore wind farms total costs with different capacity; (**b**) shows the 50 km offshore wind farms total costs with different capacity; (**c**) shows the 75 km offshore wind farms total costs with different capacity.

Still, the lowest economic costs with different capacities are seen in the hybrid HVDC transmission concept, followed by HVAC electrical transmission and VSC-HVDC transmission. The GIL system increases significantly with a longer transmission distance; so, GIL is not recommended. Considering both economic and technical feasibility, for the offshore wind farms with different distances and transmission capacities, at present, HVAC transmission and VSC-HVDC transmission are selected according to the actual situation. The total costs are more sensitive to the distance than capacity. What is more, there is a need to notice that the hybrid HVDC transmission system is a preferred choice with the economic potential for either large-capacity or long-distance wind farms.
