POSSPOW: Possible Power of Offshore Wind Power Plants

Introduction
In recent years, the very large offshore wind farms were designed as wind power plants, including possibilities to contribute to the stability of the grid by offering grid services (also called ancillary services). One of those services is reserve power, which is achieved by down-regulating the wind farm from its maximum possible power. The power can be ramped up quite quickly, but the influence of wakes makes it difficult to assess the exact amount of down-regulation available to sell. Currently, Transmission System Operators (TSOs) have no real way to determine exactly the possible power of a down-regulated wind farm.
Approach
The technology we want to develop draws together models from various disciplines, including wake modelling of large offshore wind farms, aerodynamic models for wind turbines, stochastic model estimation and computer simulations. During the project, the findings will be verified on some of the large offshore wind farms owned by Vattenfall, and possibly in a DONG Energy wind farm too. Dedicated experiments to the wind flow in large offshore wind farms are planned.
Main body of abstract
Modern wind turbines have a SCADA signal called possible power. In normal operation, this would be the actual power, but during down-regulation it would give the possible power given the current wind regime. In a down-regulated wind farm, the sum of the possible and actual power during down-regulation is not the same as the regulation power reserve in that wind farm, since turbines downwind of down-regulated turbines see more wind that would be there without the regulation.
Wake modelling is necessary in order to take into account that the wakes will change when the wind farm is down regulated. The PossPOW project will not develop new wake models, but adjust the Dynamic Wake Meandering model and/or Fuga for real-time use.
The proposed technique is to use the same wake model for two steps to calculate possible power in a down regulated case:
1. First, the ambient flow will be derived in the actual down regulated case, using wind turbines thrusts from the down regulated wind turbines. This is an inverse way of using wake models, using the wake flow as input and the ambient flow as output.
2. Secondly, the wake flow in the possible power case will be derived from the ambient flow derived in 1, using wind turbines thrusts in the possible power case. This is the normal way of using wake models, using the ambient flow as input and wake flow as output.
Conclusion
The poster presents a new Danish project on the possible power from a down-regulated wind farm. Project partners are DTU, Vestas, Siemens, Vattenfall and DONG. We aim at a verified and internationally accepted way to determine the possible power of a down-regulated offshore wind farm, taking into account the meteorology and wake effects. Along the way, we also aim at improving the use of wake models for real-time cases. Please see posspow.dtu.dk.