Comparison of operation and maintenance of floating 14MW turbines and twin 10MW turbines

Turbine ratings in the past decade have grown unexpectedly fast. In 2021 Siemens Gamesa and GE revealed their new 14MW turbine models, and it is predicted that this is not yet the rating limit that turbines can reach. Increased turbine ratings can also be achieved by putting two turbines on a single foundation. This study analyses how Operation & Maintenance (O&M) would differ if a floating wind farm had twin 10MW turbines installed on each substructure, instead of a single 14MW turbine. This study demonstrates how the strategic O&M simulation tool COMPASS can be used to perform this comparison. Assumptions regarding the O&M of twin turbines were estimated with the major floating twin turbine developer Hexicon AB. This study analyzed four cases - a case with 35 twin 10MW turbines, and three cases with 50 single 14MW turbines - to understand the potential effect of increased consumable costs, spare part lead times and maintenance durations. All cases had the same wind farm capacity of 700MW. The results show that O&M for cases with single turbines is at least 4.5% more expensive than the case with twin turbines. The case with twin turbines also resulted in a higher availability than any other case. Additionally, results showed that Operational Expenditure (OPEX) for the cases with single turbines is at least 6.0% higher in scenarios with single turbines than in the twin turbine scenario. The biggest cost contributors to the difference between scenarios were craft costs, particularly cable laying vessels and tugs. Due to the higher number of cables required for the scenario with single turbines, there is more frequent mobilization of cable vessels for cable repairs.