CERC — Environmental Software and Services

Wind energy

Wind energy is an established and sustainable method of electricity production but it is commonly criticised for its variability and unpredictability. These characteristics are partly due to the variable nature of wind, but also partly due to the impacts that wind turbines, which take energy from the wind, have on other wind turbines within the same wind farm. Highly complex models have been developed to simulate the detailed airflow around wind turbines, particularly for offshore sites, however many of these are too computationally expensive to use for operational forecasting of wind farm energy production. In contrast, the practical models that are often used to predict energy production for onshore wind farms do not properly account for the effects that surface characteristics, such as topography and land use, or meteorological effects, such as convection or stratification, have on local airflow and therefore on energy production.

CERC has developed FLOWSTAR-Energy as a practical tool for predicting wind farm energy production during design and operation at both onshore and offshore sites. FLOWSTAR-Energy includes a model for airflow over complex surfaces (FLOWSTAR) and a wind turbine wake model. The wake model simulates the effect of one wind turbine on another turbine by exploiting similarities between the behaviour of a wind turbine wake and the dispersion of a plume of passive gas. An important feature of the model is that it estimates the vertical structure of the atmospheric boundary layer from standard meteorological parameters measured at the surface, so that the effects of atmospheric stability can be included.

Carbon Trust: Offshore Wind Accelerator

In 2013, CERC carried out a project for the Carbon Trust to develop a mesoscale modelling method for the investigation of offshore wind farm wake effects, as part of the Offshore Wind Accelerator (OWA) Programme. The main objective of the project was to investigate the capability of a mesoscale modelling approach to estimate the long-range wake influence from one offshore wind farm on the yield of another.

As part of this work, CERC completed a review of candidate mesoscale models, covering their main features, advantages and disadvantages relevant to their offshore use. CERC, together with the Hong Kong University of Science and Technology, ran the mesoscale model WRF, in conjunction with a beta version of FLOWSTAR-Energy, to calculate wind speed, turbulence and wind farm power output, over a simulation period of one year.

TOPFARM: modelling wind turbine wakes with ADMS

Between 2008 and 2011, CERC was a partner in an EU sponsored project to design and demonstrate a Next generation design tool for optimisation of wind farm topology and operation. The project was particularly concerned with large wind farms, either onshore or offshore, where turbines in the interior are affected by the wakes from upwind turbines in the following ways:

TOPFARM wind speed imageTOPFARM sigma-u image

(Click to enlarge)

  • reduction in turbine inflow wind speed, causing lower energy production; and
  • increased turbulence in inflow, causing elevated loading and therefore increased fatigue.

CERC's role was to develop ADMS to model the wind speed deficit in the wake of a turbine as a meandering turbulent plume, and to use ADMS's fluctuations module to analyse the turbulent fluctuations generated by wake meandering, including the interaction between wakes.

This work led to the development of the FLOWSTAR-Energy model, which combines the wake model initially developed during TOPFARM with CERCís FLOWSTAR model of airflow over complex terrain.

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