By Renewable Energy Focus staff

The costs in question generally cover expenses which depend on the topology of the wind farm, such as: Costs associated with operation and maintenance; costs related to the fatigue load of the main components of a wind turbine and start-up expenses related to foundations, grid, roads.

”A selected case analysis of Middelgrunden Windfarm has shown that exactly the expenses to establish, for example, an electricity network mean a lot to the total benefit. The analysis furthermore shows that the load caused by turbulent wakes behind each wind turbine could have an impact on the optimum wind farm topology and thus on the economy of a wind farm – this aspect would naturally not be considered by an optimisation model exclusively relying on the final product, namely power generation," says Gunner Chr. Larsen, Senior Scientist at Risø DTU, who has been the project coordinator for TOPFARM.

The core of the optimisation tool consists of five calculation modules:

1. The first module consists of models (of varying complexity) that describe the wind inside a wind farm;
2. The second module is a detailed model of how the wind affects each wind turbine in a wind farm. The input to this module is the wind field from the first module and the result is production data and load data from the individual turbines;
3. The third module comprises models of the control system at both wind farm level and wind turbine level;
4. The fourth module contains cost models, which make it possible to formulate the optimisation problem in economic terms for the wind farm; and
5. The fifth and the last module is a package of optimisation algorithms that, with the input from the other four modules, generates the optimum layout of a given wind farm.

The latter is the module that gave rise in the case story to the new location of wind turbines at Middelgrunden wind farm.

”For example, the costs of the wearing down caused by load must be deducted from the direct economic output of the wind farm – power generation – because of the consequent repair and reduced service life of key wind turbine components. But also startup expenses, which are directly affected by the location, can be crucial to the economy – e. g. at sea where foundation costs typically depend on the depth of water. Should the turbines be arranged differently so that they 'provide less shade’ from each other? Or is it necessary to build a road or some other infrastructure in connection with a particular location for wind turbines in a wind farm? If so, it is important to include these considerations in your calculations,” Larsen explains.

Next step

The TOPFARM optimisation platform is currently a research tool, but the vision of the scientists at Risø DTU is to pursue opportunities with the purpose of creating a more user-friendly programme that can be used by wind farm developers in their daily work.