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When are forest or mountain sites suitable for wind farms?

A forest trail in the Arnsberger Wald in North Rhine-Westphalia/Germany, tall fir trees, green hills in the distance. It’s pretty much always windy here. A good location for a wind farm?

‘That depends’, says Christoph Hilling, Head of Wind & Site Engineering at ENERCON. ‘That the wind is blowing is not enough – it is also important how it’s blowing.’ Together with his team at ENERCON Wind & Site Engineering, Christoph Hilling assesses the wind conditions of specific projects – more than 1,000 per year. And these can be quite complex at times.  

‘In lowland areas, calculating the wind conditions is pretty easy. Forested or mountainous landscapes, on the other hand, represent more complex wind systems’, says Dr Sebastian Remmler, wind flow modelling expert at ENERCON Site Analytics. This is because of flow separation on mountain slopes or wind shear – in other words, conditions in which the speed and direction of the wind vary widely and can therefore put particular loads on the components of wind energy converters.  

‘At ENERCON, site complexity in and of itself has never been an exclusion criterion for project realisation. On the contrary – given the limited land area available for wind power expansion, more and more forested or mountainous sites must be taken into consideration’, says Dr Marcus Letzel, Head of Site Analytics & Meteorology at ENERCON. ‘But in order to make a realistic assessment of the risks and ultimately the commercial success of a project, we need to understand the precise flow conditions at each individual WEC location at different heights. To do so, the quality of the simulation is key.’

The simulation capabilities of E-Wind, ENERCON’s proprietary CFD software, have been improved yet again in the latest version. ‘We started using E-Wind in 2017, and we are continuously optimising the tool with regard to automation, quality, integration into process chains and the graphic display’, says Judith Langner, E-Wind developer at Site Analytics. ‘The latest update allows us to perform even more extensive analyses of potentially risky wind conditions at individual WEC positions – and this is already possible at the planning stage.’ The prerequisites for this process include digital topographical maps and land use maps as well as detailed local measurement data for calibrating the simulation parameters.

‘The investment in long-term wind data measurements taken at a proposed wind farm at the height of the swept area of a potential wind energy converter pays off – in particular at complex sites’, says Christoph Hilling. Not only does it allow for the optimisation of the site layout and a more precise forecast of the annual energy yield, it also reduces the risk of a slower than expected return on investment, he adds. ‘If we feed our simulation tool with highly realistic data, we can calibrate the CFD models and use the results to derive valuable insights concerning loads, service life, or sectorial curtailment. All of these are factors that play into the commercial success of a project’, says Hilling. As an alternative to the collection of custom measuring results, ENERCON can – in less complex areas – also fall back on the extensive data from existing wind energy converters nearby.  

The steadily growing number of wind farm projects that use E-Wind calculations demonstrates the importance of E-Wind for external and internal customers for development. ENERCON’s in-house tool provides significant benefits compared to open-source solutions or commercial products. For example, ENERCON’s experts know exactly how the software works; they have full control over the quality of the results; and they can readily adjust the tool to specific requirements. In addition, it fits perfectly into the process chain so that it accelerates the entire assessment process.  Additional software features are already being planned.  

Graphic from E- Wind: The software is able to model even complex wind conditions such as flow separation and recirculation areas (‘rolled-up’ flow lines). Areas with such high-risk wind conditions are flagged automatically (dark red shading) and the project engineer receives corresponding warnings if proposed wind energy converters are affected.’

A typical picture of a potential wind farm site on a mountain top (tree damage due to bark beetles). Similar sites are assessed by the Wind & Site Engineering Team using ENERCON’s proprietary E-Wind simulation software.