Wind turbine industry is growing and future predictions are promising. However, a shortage of installation vessels could influence this growth in offshore wind industry. Commonly, wind turbines are installed in components using a jack-up vessel. Occasionally, wind turbines are installed fully assembled. The center of gravity of a fully assembled wind turbine is relatively low and thus lifting above the wind turbine is not necessarily for fully assembled wind turbine installation. Wind turbines can be installed fully assembled using cranes in twin lift configuration to reduce required lifting capacities. The flexibility and scalability of the vessel depends on the location of the cranes on the vessel. Different vessels can install wind turbines with their advantages and disadvantages. To identify these solutions, principles are proposed and compared with state-of-the-art vessels for wind turbine installations. A morphological analysis is used to identify promising solutions for fully assembled wind turbine installation. Eight concepts are compared in a scenario comparison with varying distance between nearby marshalling ports and the wind turbine park location. Several solutions show subsequent improvement in installation rates. One new concept, the PWT installation vessel, shows overall improvement in installation rates. This solution, developed by the author of this report, is proposed for flexible and scalable fully assembled wind turbine installation.