Abstract
In Denmark, the operation experience from the Horns Rev I offshore windfarm (160 MW) located in the North Sea showed that power output of the windfarm was characterised by intense, rapid and repeating fluctuations due to unsteady wind conditions. In certain wind conditions, the power output from the offshore windfarm changes between zero and rated power levels in faster than a quarter of an hour, introducing power fluctuations of a repeating character to the Danish transmission grid. Such intense power fluctuations may last for several hours, introducing a power-balance challenge to the Danish transmission system. Many transmission systems, including the Nordic system which Denmark is part of, are hourly- and quarter-hourly- based regarding the power generation plans, power balance and agreed power transmission between the countries. Applying the Nordel1 cooperation regulations and a simplified grid equivalent of a hydro-power-based transmission system with the main generation and consumption figures of Norway, this paper shows that such hourly- and quarter-hourly- system operation regulations may introduce a bottleneck for efficient utilization of available regulating power with increasing grid-integration of large offshore windfarms.