Modeling space-time correlations of velocity fluctuations in wind farms

An analytical model for the streamwise velocity space-time correlations in turbulent flows is derived and applied to the special case of velocity fluctuations in large wind farms. The model is based on the Kraichnan-Tennekes random sweeping hypothesis, capturing the decorrelation in time while including a mean wind velocity in the streamwise direction. In the resulting model, the streamwise velocity space-time correlation is expressed as a convolution of the pure space correlation with an analytical temporal decorrelation kernel. Hence, the spatio-temporal structure of velocity fluctuations in wind farms can be derived from the spatial correlations only. We then explore the applicability of the model to predict spatio-temporal correlations in turbulent flows in wind farms. Comparisons of the model with data from a large eddy simulation of flow in a large, spatially periodic wind farm are performed, where needed model parameters such as spatial and temporal integral scales and spatial correlations are determined from the large eddy simulation. Good agreement is obtained between the model and large eddy simulation data showing that spatial data may be used to model the full temporal structure of fluctuations in wind farms.Comment: Submitted to Wind Energ

Wicked facets of the German energy transition – examples from the electricity, heating, transport, and industry sectors

We shed light on wicked problems in the German energy transition. Our methods consist of a multiple-case study and multi-criteria analysis, utilising the wicked problems theoretical framework introduced by Horst Rittel and Melvin Webber [1973. “Dilemmas in a General Theory of Planning.” Policy Sciences 4 (2): 155–169. Accessed August 20, 2019. https://doi.org/10.1007/BF01405730]. Results from the energy supply, heating/cooling, transport, and industry sectors illustrate where and how the 10-point frame of wicked problems manifests in the German energy transition. The four cases exhibit more wicked tendencies in the governance domain than the technical domain and differ in their degrees of technology maturity, policy regulation, and knowledge states. We do not find that the German energy transition is inherently wicked. However, wickedness unfolds through the social setting into which technical solutions of the energy transition are embedded. We aim to highlight these intricacies and encourage scrutinising these wicked facets early on

Wicked facets of the German energy transition – examples from the electricity, heating, transport, and industry sectors

We shed light on wicked problems in the German energy transition. Our methods consist of a multiple-case study and multi-criteria analysis, utilising the wicked problems theoretical framework introduced by Horst Rittel and Melvin Webber [1973. “Dilemmas in a General Theory of Planning.” Policy Sciences 4 (2): 155–169. Accessed August 20, 2019. https://doi.org/10.1007/BF01405730]. Results from the energy supply, heating/cooling, transport, and industry sectors illustrate where and how the 10-point frame of wicked problems manifests in the German energy transition. The four cases exhibit more wicked tendencies in the governance domain than the technical domain and differ in their degrees of technology maturity, policy regulation, and knowledge states. We do not find that the German energy transition is inherently wicked. However, wickedness unfolds through the social setting into which technical solutions of the energy transition are embedded. We aim to highlight these intricacies and encourage scrutinising these wicked facets early on