Influence of Technical Limitations and Operation on Sizing of an Offshore Energy Storage Connected to an Offshore Wind Farm

Abstract This paper aims to investigate the sizing of an offshore energy storage unit operated in conjunction with an offshore wind farm. The storage unit is evaluated with technical limitations to reveal the parameter sensitivities when coupled with a wind farm. The main interest is the sizing of the storage unit for capacity firming purposes. A storage unit in combination with a large offshore wind farm has been simulated in time domain over the course of one year. The storage unit has been operated with the goal of firming the wind power capacity within each bid period. Different constraints have been introduced to show parameter sensitivity of the storage unit. The constraints were both technical and control oriented. An important prerequisite for the simulation was that the combined wind power plant and the storage operate in a market where the imbalance between bid and delivered energy is measured and penalized. Results show that there are several important parameters regarding storage sizing. Storage sizing is shown to be very dependent on the production forecast error and market bid length. Furthermore, technical constraints in the shape of ramping rates and power reversal dead time can be countered by choosing an appropriate control strategy. No control strategy gives significantly more reduction in grid power imbalance than the constant, fixed mode control strategy. The same reduction can however be obtained, with somewhat less energy routed through the storage by applying an alternative control strategy.