Offshore Wind Transmission Systems - Power Grid Integration Techno-economic analysis of HVAC, HVDC, and LFAC

Abstract

Abstract Offshore wind has turned into one of the most promising sources of renewable energy and the offshore wind industry is a rapidly growing business at this moment in time. This paper compares technical and economic aspects of the export systems associated with transmitting active power by offshore wind farms using High Voltage Alternating current (HVAC), High Voltage Direct Current (HVDC), and Low-Frequency Alternating Current (LFAC). This study investigated offshore wind farms with installed active power ranging from 300 MW to 1400 MW located 20 km to 200 km from shore. For each configuration, 120 models were dimensioned and implemented in PowerFactory such that load-flow analysis could be performed. Each model in PowerFactory corresponds to a certain power level and distance. The load-flow studies resulted in the ratings of the main equipment for each system, later being used as the input data for the economic evaluation. As the ratings of the components were set, Capital Expenditures (CAPEX) and Levelized Cost of Electricity (LCOE) analysis were performed to evaluate the techno-economic distance for each configuration. The Key Performace Indicator (KPI) LCOE concluded that HVAC was the suitable topology for distances from 0 km up to 140 - 160 km. A steady decline in breakeven distance can be found as the active power increases. HVAC cables became the driving force of the CAPEX and Operational Expenditures (OPEX) the further away from shore the wind farm is located. HVDC required a large initial investment for the platform and converters, but considerably cheaper cables make it suitable for long-distance transmission. The break-even distance for HVDC was found at roughly 150 km. Furthermore, the optimal techno-economic range for LFAC was confined to low-power, long-distance applications. Its break-even point was found at distances over 160 km, and an installed active power ranging from 300 - 500 MW. Lastly, a sensitivity analysis was performed at the cost of the SFC (Static Frequency Converter). If the cost was reduced, the break-even point between LFAC and HVAC would remain the same while it would gain some distance from the HVDC case. As the cost was increased, the business case for LFAC according to the LCOE analysis vanished.