Optimal timing of wind farm repowering: a two-factor real options analysis

ABSTRACT For more than twenty years now, wind power has been one of the main renewable energy sources. Whereas offshore wind utilization still has a high risk profile, the repowering of wind converters offers an interesting alternative to further increase the use of renewable energy. This paper studies the economics and optimal timing of repowering. We use a two-factor real options modeling framework that builds upon McDonald and Siegel's 1986 approach. It allows consideration of the investment costs as well as revenues, both following a continuous time, stochastic process. In the next step, a Monte Carlo simulation is done to determine the probability of success of repowering for each year. Finally, we discuss the results of increasing repowering activities and highlight the efforts necessary to achieve this. The model is applied to the case of repowering a 4 X 450 kW wind farm in Denmark to one with 3 X 2 MW. We find that until now the high uncertainty in Denmark in terms of revenues has hindered further development of repowering and lowered the probability of success significantly, while the selling price of the used turbines has had only a minor effect on the optimal timing of repowering. Therefore, wind developers should argue for a larger stake of secured parts in revenues, achievable via higher government-guaranteed incentives.