Cost analysis and comparison of HVAC, LFAC and HVDC for offshore wind power connection

Low frequency AC (LFAC) has been proposed as a means to avoid some of the large converter station costs of high voltage DC (HVDC) while delivering some of the benefits in terms of better cable utilization and its technical feasibility has been established. It is said to offer lower costs than HVDC or conventional high voltage AC (HVAC) for a range of intermediate distances, with HVDC becoming cheaper over long distances. However, the basis for identifying the distance range and extent of cost saving has not been established. Here, cost estimate methodologies are extended for LFAC. A difficulty is the absence of commercial schemes that can provide practical examples of costs. In this paper, costs are broken down into constituent terms and estimates are made from the most similar equipment from other schemes. The capacity limits and power losses associated with subsea cables are analyzed for low frequency cases. For a given power transfer and for each distance, a choice of operating voltage, cable size and number of parallel circuits is made in order to find the lowest route cost. This yields cost as a function of distance that is a non-linear and discontinuous function. The cost curves for LFAC are compared with HVDC and HVAC options. The results for current cost estimates show that LFAC has a range of route length over which it is the lowest cost option and but this range narrows and eventually ceases to exist for higher power transfer ratings.